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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
#include "jit/IonAnalysis.h"
#include "mozilla/HashFunctions.h"
#include <algorithm>
#include <utility> // for ::std::pair
#include "jit/AliasAnalysis.h"
#include "jit/CompileInfo.h"
#include "jit/DominatorTree.h"
#include "jit/MIRGenerator.h"
#include "jit/MIRGraph.h"
#include "util/CheckedArithmetic.h"
#include "vm/BytecodeUtil-inl.h"
using namespace js;
using namespace js::jit;
using mozilla::DebugOnly;
// Stack used by FlagPhiInputsAsImplicitlyUsed. It stores the Phi instruction
// pointer and the MUseIterator which should be visited next.
using MPhiUseIteratorStack =
Vector<std::pair<MPhi*, MUseIterator>, 16, SystemAllocPolicy>;
// Look for Phi uses with a depth-first search. If any uses are found the stack
// of MPhi instructions is returned in the |worklist| argument.
[[nodiscard]] static bool DepthFirstSearchUse(const MIRGenerator* mir,
MPhiUseIteratorStack& worklist,
MPhi* phi) {
// Push a Phi and the next use to iterate over in the worklist.
auto push = [&worklist](MPhi* phi, MUseIterator use) -> bool {
phi->setInWorklist();
return worklist.append(std::make_pair(phi, use));
};
#ifdef DEBUG
// Used to assert that when we have no uses, we at least visited all the
// transitive uses.
size_t refUseCount = phi->useCount();
size_t useCount = 0;
#endif
MOZ_ASSERT(worklist.empty());
if (!push(phi, phi->usesBegin())) {
return false;
}
while (!worklist.empty()) {
// Resume iterating over the last phi-use pair added by the next loop.
auto pair = worklist.popCopy();
MPhi* producer = pair.first;
MUseIterator use = pair.second;
MUseIterator end(producer->usesEnd());
producer->setNotInWorklist();
// Keep going down the tree of uses, skipping (continue)
// non-observable/unused cases and Phi which are already listed in the
// worklist. Stop (return) as soon as one use is found.
while (use != end) {
MNode* consumer = (*use)->consumer();
MUseIterator it = use;
use++;
#ifdef DEBUG
useCount++;
#endif
if (mir->shouldCancel("FlagPhiInputsAsImplicitlyUsed inner loop")) {
return false;
}
if (consumer->isResumePoint()) {
MResumePoint* rp = consumer->toResumePoint();
// Observable operands are similar to potential uses.
if (rp->isObservableOperand(*it)) {
return push(producer, use);
}
continue;
}
MDefinition* cdef = consumer->toDefinition();
if (!cdef->isPhi()) {
// The producer is explicitly used by a definition.
return push(producer, use);
}
MPhi* cphi = cdef->toPhi();
if (cphi->getUsageAnalysis() == PhiUsage::Used ||
cphi->isImplicitlyUsed()) {
// The information got cached on the Phi the last time it
// got visited, or when flagging operands of implicitly used
// instructions.
return push(producer, use);
}
if (cphi->isInWorklist() || cphi == producer) {
// We are already iterating over the uses of this Phi instruction which
// are part of a loop, instead of trying to handle loops, conservatively
// mark them as used.
return push(producer, use);
}
if (cphi->getUsageAnalysis() == PhiUsage::Unused) {
// The instruction already got visited and is known to have
// no uses. Skip it.
continue;
}
// We found another Phi instruction, move the use iterator to
// the next use push it to the worklist stack. Then, continue
// with a depth search.
if (!push(producer, use)) {
return false;
}
producer = cphi;
use = producer->usesBegin();
end = producer->usesEnd();
#ifdef DEBUG
refUseCount += producer->useCount();
#endif
}
// When unused, we cannot bubble up this information without iterating
// over the rest of the previous Phi instruction consumers.
MOZ_ASSERT(use == end);
producer->setUsageAnalysis(PhiUsage::Unused);
}
MOZ_ASSERT(useCount == refUseCount);
return true;
}
[[nodiscard]] static bool FlagPhiInputsAsImplicitlyUsed(
const MIRGenerator* mir, MBasicBlock* block, MBasicBlock* succ,
MPhiUseIteratorStack& worklist) {
// When removing an edge between 2 blocks, we might remove the ability of
// later phases to figure out that the uses of a Phi should be considered as
// a use of all its inputs. Thus we need to mark the Phi inputs as being
// implicitly used iff the phi has any uses.
//
//
// +--------------------+ +---------------------+
// |12 MFoo 6 | |32 MBar 5 |
// | | | |
// | ... | | ... |
// | | | |
// |25 MGoto Block 4 | |43 MGoto Block 4 |
// +--------------------+ +---------------------+
// | |
// | | |
// | | |
// | +-----X------------------------+
// | Edge |
// | Removed |
// | |
// | +------------v-----------+
// | |50 MPhi 12 32 |
// | | |
// | | ... |
// | | |
// | |70 MReturn 50 |
// | +------------------------+
// |
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// |
// v
//
// ^ +--------------------+ +---------------------+
// /!\ |12 MConst opt-out | |32 MBar 5 |
// '---' | | | |
// | ... | | ... |
// |78 MBail | | |
// |80 MUnreachable | |43 MGoto Block 4 |
// +--------------------+ +---------------------+
// |
// |
// |
// +---------------+
// |
// |
// |
// +------------v-----------+
// |50 MPhi 32 |
// | |
// | ... |
// | |
// |70 MReturn 50 |
// +------------------------+
//
//
// If the inputs of the Phi are not flagged as implicitly used, then
// later compilation phase might optimize them out. The problem is that a
// bailout will use this value and give it back to baseline, which will then
// use the OptimizedOut magic value in a computation.
//
// Unfortunately, we cannot be too conservative about flagging Phi inputs as
// having implicit uses, as this would prevent many optimizations from being
// used. Thus, the following code is in charge of flagging Phi instructions
// as Unused or Used, and setting ImplicitlyUsed accordingly.
size_t predIndex = succ->getPredecessorIndex(block);
MPhiIterator end = succ->phisEnd();
MPhiIterator it = succ->phisBegin();
for (; it != end; it++) {
MPhi* phi = *it;
if (mir->shouldCancel("FlagPhiInputsAsImplicitlyUsed outer loop")) {
return false;
}
// We are looking to mark the Phi inputs which are used across the edge
// between the |block| and its successor |succ|.
MDefinition* def = phi->getOperand(predIndex);
if (def->isImplicitlyUsed()) {
continue;
}
// If the Phi is either Used or Unused, set the ImplicitlyUsed flag
// accordingly.
if (phi->getUsageAnalysis() == PhiUsage::Used || phi->isImplicitlyUsed()) {
def->setImplicitlyUsedUnchecked();
continue;
} else if (phi->getUsageAnalysis() == PhiUsage::Unused) {
continue;
}
// We do not know if the Phi was Used or Unused, iterate over all uses
// with a depth-search of uses. Returns the matching stack in the
// worklist as soon as one use is found.
MOZ_ASSERT(worklist.empty());
if (!DepthFirstSearchUse(mir, worklist, phi)) {
return false;
}
MOZ_ASSERT_IF(worklist.empty(),
phi->getUsageAnalysis() == PhiUsage::Unused);
if (!worklist.empty()) {
// One of the Phis is used, set Used flags on all the Phis which are
// in the use chain.
def->setImplicitlyUsedUnchecked();
do {
auto pair = worklist.popCopy();
MPhi* producer = pair.first;
producer->setUsageAnalysis(PhiUsage::Used);
producer->setNotInWorklist();
} while (!worklist.empty());
}
MOZ_ASSERT(phi->getUsageAnalysis() != PhiUsage::Unknown);
}
return true;
}
static MInstructionIterator FindFirstInstructionAfterBail(MBasicBlock* block) {
MOZ_ASSERT(block->alwaysBails());
for (MInstructionIterator it = block->begin(); it != block->end(); it++) {
MInstruction* ins = *it;
if (ins->isBail()) {
it++;
return it;
}
}
MOZ_CRASH("Expected MBail in alwaysBails block");
}
// Given an iterator pointing to the first removed instruction, mark
// the operands of each removed instruction as having implicit uses.
[[nodiscard]] static bool FlagOperandsAsImplicitlyUsedAfter(
const MIRGenerator* mir, MBasicBlock* block,
MInstructionIterator firstRemoved) {
MOZ_ASSERT(firstRemoved->block() == block);
const CompileInfo& info = block->info();
// Flag operands of removed instructions as having implicit uses.
MInstructionIterator end = block->end();
for (MInstructionIterator it = firstRemoved; it != end; it++) {
if (mir->shouldCancel("FlagOperandsAsImplicitlyUsedAfter (loop 1)")) {
return false;
}
MInstruction* ins = *it;
for (size_t i = 0, e = ins->numOperands(); i < e; i++) {
ins->getOperand(i)->setImplicitlyUsedUnchecked();
}
// Flag observable resume point operands as having implicit uses.
if (MResumePoint* rp = ins->resumePoint()) {
// Note: no need to iterate over the caller's of the resume point as
// this is the same as the entry resume point.
MOZ_ASSERT(&rp->block()->info() == &info);
for (size_t i = 0, e = rp->numOperands(); i < e; i++) {
if (info.isObservableSlot(i)) {
rp->getOperand(i)->setImplicitlyUsedUnchecked();
}
}
}
}
// Flag Phi inputs of the successors as having implicit uses.
MPhiUseIteratorStack worklist;
for (size_t i = 0, e = block->numSuccessors(); i < e; i++) {
if (mir->shouldCancel("FlagOperandsAsImplicitlyUsedAfter (loop 2)")) {
return false;
}
if (!FlagPhiInputsAsImplicitlyUsed(mir, block, block->getSuccessor(i),
worklist)) {
return false;
}
}
return true;
}
[[nodiscard]] static bool FlagEntryResumePointOperands(const MIRGenerator* mir,
MBasicBlock* block) {
// Flag observable operands of the entry resume point as having implicit uses.
MResumePoint* rp = block->entryResumePoint();
while (rp) {
if (mir->shouldCancel("FlagEntryResumePointOperands")) {
return false;
}
const CompileInfo& info = rp->block()->info();
for (size_t i = 0, e = rp->numOperands(); i < e; i++) {
if (info.isObservableSlot(i)) {
rp->getOperand(i)->setImplicitlyUsedUnchecked();
}
}
rp = rp->caller();
}
return true;
}
[[nodiscard]] static bool FlagAllOperandsAsImplicitlyUsed(
const MIRGenerator* mir, MBasicBlock* block) {
return FlagEntryResumePointOperands(mir, block) &&
FlagOperandsAsImplicitlyUsedAfter(mir, block, block->begin());
}
// WarpBuilder sets the alwaysBails flag on blocks that contain an
// unconditional bailout. We trim any instructions in those blocks
// after the first unconditional bailout, and remove any blocks that
// are only reachable through bailing blocks.
bool jit::PruneUnusedBranches(const MIRGenerator* mir, MIRGraph& graph) {
JitSpew(JitSpew_Prune, "Begin");
// Pruning is guided by unconditional bailouts. Wasm does not have bailouts.
MOZ_ASSERT(!mir->compilingWasm());
Vector<MBasicBlock*, 16, SystemAllocPolicy> worklist;
uint32_t numMarked = 0;
bool needsTrim = false;
auto markReachable = [&](MBasicBlock* block) -> bool {
block->mark();
numMarked++;
if (block->alwaysBails()) {
needsTrim = true;
}
return worklist.append(block);
};
// The entry block is always reachable.
if (!markReachable(graph.entryBlock())) {
return false;
}
// The OSR entry block is always reachable if it exists.
if (graph.osrBlock() && !markReachable(graph.osrBlock())) {
return false;
}
// Iteratively mark all reachable blocks.
while (!worklist.empty()) {
if (mir->shouldCancel("Prune unused branches (marking reachable)")) {
return false;
}
MBasicBlock* block = worklist.popCopy();
JitSpew(JitSpew_Prune, "Visit block %u:", block->id());
JitSpewIndent indent(JitSpew_Prune);
// If this block always bails, then it does not reach its successors.
if (block->alwaysBails()) {
continue;
}
for (size_t i = 0; i < block->numSuccessors(); i++) {
MBasicBlock* succ = block->getSuccessor(i);
if (succ->isMarked()) {
continue;
}
JitSpew(JitSpew_Prune, "Reaches block %u", succ->id());
if (!markReachable(succ)) {
return false;
}
}
}
if (!needsTrim && numMarked == graph.numBlocks()) {
// There is nothing to prune.
graph.unmarkBlocks();
return true;
}
JitSpew(JitSpew_Prune, "Remove unreachable instructions and blocks:");
JitSpewIndent indent(JitSpew_Prune);
// The operands of removed instructions may be needed in baseline
// after bailing out.
for (PostorderIterator it(graph.poBegin()); it != graph.poEnd();) {
if (mir->shouldCancel("Prune unused branches (marking operands)")) {
return false;
}
MBasicBlock* block = *it++;
if (!block->isMarked()) {
// If we are removing the block entirely, mark the operands of every
// instruction as being implicitly used.
if (!FlagAllOperandsAsImplicitlyUsed(mir, block)) {
return false;
}
} else if (block->alwaysBails()) {
// If we are only trimming instructions after a bail, only mark operands
// of removed instructions.
MInstructionIterator firstRemoved = FindFirstInstructionAfterBail(block);
if (!FlagOperandsAsImplicitlyUsedAfter(mir, block, firstRemoved)) {
return false;
}
}
}
// Remove the blocks in post-order such that consumers are visited before
// the predecessors, the only exception being the Phi nodes of loop headers.
for (PostorderIterator it(graph.poBegin()); it != graph.poEnd();) {
if (mir->shouldCancel("Prune unused branches (removal loop)")) {
return false;
}
if (!graph.alloc().ensureBallast()) {
return false;
}
MBasicBlock* block = *it++;
if (block->isMarked() && !block->alwaysBails()) {
continue;
}
// As we are going to replace/remove the last instruction, we first have
// to remove this block from the predecessor list of its successors.
size_t numSucc = block->numSuccessors();
for (uint32_t i = 0; i < numSucc; i++) {
MBasicBlock* succ = block->getSuccessor(i);
if (succ->isDead()) {
continue;
}
// Our dominators code expects all loop headers to have two predecessors.
// If we are removing the normal entry to a loop, but can still reach
// the loop header via OSR, we create a fake unreachable predecessor.
if (succ->isLoopHeader() && block != succ->backedge()) {
MOZ_ASSERT(graph.osrBlock());
if (!graph.alloc().ensureBallast()) {
return false;
}
MBasicBlock* fake = MBasicBlock::NewFakeLoopPredecessor(graph, succ);
if (!fake) {
return false;
}
// Mark the block to avoid removing it as unreachable.
fake->mark();
JitSpew(JitSpew_Prune,
"Header %u only reachable by OSR. Add fake predecessor %u",
succ->id(), fake->id());
}
JitSpew(JitSpew_Prune, "Remove block edge %u -> %u.", block->id(),
succ->id());
succ->removePredecessor(block);
}
if (!block->isMarked()) {
// Remove unreachable blocks from the CFG.
JitSpew(JitSpew_Prune, "Remove block %u.", block->id());
graph.removeBlock(block);
} else {
// Remove unreachable instructions after unconditional bailouts.
JitSpew(JitSpew_Prune, "Trim block %u.", block->id());
// Discard all instructions after the first MBail.
MInstructionIterator firstRemoved = FindFirstInstructionAfterBail(block);
block->discardAllInstructionsStartingAt(firstRemoved);
if (block->outerResumePoint()) {
block->clearOuterResumePoint();
}
block->end(MUnreachable::New(graph.alloc()));
}
}
graph.unmarkBlocks();
return true;
}
[[nodiscard]] static bool SplitCriticalEdgesForBlock(MIRGraph& graph,
MBasicBlock* block) {
if (block->numSuccessors() < 2) {
return true;
}
for (size_t i = 0; i < block->numSuccessors(); i++) {
MBasicBlock* target = block->getSuccessor(i);
if (target->numPredecessors() < 2) {
continue;
}
// Create a simple new block which contains a goto and which split the
// edge between block and target.
MBasicBlock* split = MBasicBlock::NewSplitEdge(graph, block, i, target);
if (!split) {
return false;
}
}
return true;
}
// A critical edge is an edge which is neither its successor's only predecessor
// nor its predecessor's only successor. Critical edges must be split to
// prevent copy-insertion and code motion from affecting other edges.
bool jit::SplitCriticalEdges(MIRGraph& graph) {
for (MBasicBlockIterator iter(graph.begin()); iter != graph.end(); iter++) {
MBasicBlock* block = *iter;
if (!SplitCriticalEdgesForBlock(graph, block)) {
return false;
}
}
return true;
}
bool jit::IsUint32Type(const MDefinition* def) {
if (def->isBeta()) {
def = def->getOperand(0);
}
if (def->type() != MIRType::Int32) {
return false;
}
return def->isUrsh() && def->getOperand(1)->isConstant() &&
def->getOperand(1)->toConstant()->type() == MIRType::Int32 &&
def->getOperand(1)->toConstant()->toInt32() == 0;
}
// Determine whether phiBlock/testBlock simply compute a phi and perform a
// test on it.
static bool BlockIsSingleTest(MBasicBlock* phiBlock, MBasicBlock* testBlock,
MPhi** pphi, MTest** ptest) {
*pphi = nullptr;
*ptest = nullptr;
if (phiBlock != testBlock) {
MOZ_ASSERT(phiBlock->numSuccessors() == 1 &&
phiBlock->getSuccessor(0) == testBlock);
if (!phiBlock->begin()->isGoto()) {
return false;
}
}
auto iter = testBlock->rbegin();
if (!iter->isTest()) {
return false;
}
MTest* test = iter->toTest();
// Unwrap boolean conversion performed through the '!!' idiom.
MInstruction* testOrNot = test;
bool hasOddNumberOfNots = false;
while (++iter != testBlock->rend()) {
if (iter->isNot()) {
// The MNot must only be used by |testOrNot|.
auto* notIns = iter->toNot();
if (testOrNot->getOperand(0) != notIns) {
return false;
}
if (!notIns->hasOneUse()) {
return false;
}
testOrNot = notIns;
hasOddNumberOfNots = !hasOddNumberOfNots;
} else {
// Fail if there are any other instructions than MNot.
return false;
}
}
// There's an odd number of MNot, so this can't be the '!!' idiom.
if (hasOddNumberOfNots) {
return false;
}
MOZ_ASSERT(testOrNot->isTest() || testOrNot->isNot());
MDefinition* testInput = testOrNot->getOperand(0);
if (!testInput->isPhi()) {
return false;
}
MPhi* phi = testInput->toPhi();
if (phi->block() != phiBlock) {
return false;
}
for (MUseIterator iter = phi->usesBegin(); iter != phi->usesEnd(); ++iter) {
MUse* use = *iter;
if (use->consumer() == testOrNot) {
continue;
}
if (use->consumer()->isResumePoint()) {
MBasicBlock* useBlock = use->consumer()->block();
if (useBlock == phiBlock || useBlock == testBlock) {
continue;
}
}
return false;
}
for (MPhiIterator iter = phiBlock->phisBegin(); iter != phiBlock->phisEnd();
++iter) {
if (*iter != phi) {
return false;
}
}
if (phiBlock != testBlock && !testBlock->phisEmpty()) {
return false;
}
*pphi = phi;
*ptest = test;
return true;
}
// Determine if value is directly or indirectly the test input.
static bool IsTestInputMaybeToBool(MTest* test, MDefinition* value) {
auto* input = test->input();
bool hasEvenNumberOfNots = true;
while (true) {
// Only accept if there's an even number of MNot.
if (input == value && hasEvenNumberOfNots) {
return true;
}
// Unwrap boolean conversion performed through the '!!' idiom.
if (input->isNot()) {
input = input->toNot()->input();
hasEvenNumberOfNots = !hasEvenNumberOfNots;
continue;
}
return false;
}
}
// Change |block| so that it ends in a goto to the specific |target| block.
// |existingPred| is an existing predecessor of the block.
//
// |blockResult| is the value computed by |block|. This was a phi input but the
// caller has determined that |blockResult| matches the input of an earlier
// MTest instruction and we don't need to test it a second time. Mark it as
// implicitly-used because we're removing a use.
[[nodiscard]] static bool UpdateGotoSuccessor(TempAllocator& alloc,
MBasicBlock* block,
MDefinition* blockResult,
MBasicBlock* target,
MBasicBlock* existingPred) {
blockResult->setImplicitlyUsedUnchecked();
MInstruction* ins = block->lastIns();
MOZ_ASSERT(ins->isGoto());
ins->toGoto()->target()->removePredecessor(block);
block->discardLastIns();
MGoto* newGoto = MGoto::New(alloc, target);
block->end(newGoto);
return target->addPredecessorSameInputsAs(block, existingPred);
}
// Change block so that it ends in a test of the specified value, going to
// either ifTrue or ifFalse. existingPred is an existing predecessor of ifTrue
// or ifFalse with the same values incoming to ifTrue/ifFalse as block.
// existingPred is not required to be a predecessor of ifTrue/ifFalse if block
// already ends in a test going to that block on a true/false result.
[[nodiscard]] static bool UpdateTestSuccessors(
TempAllocator& alloc, MBasicBlock* block, MDefinition* value,
MBasicBlock* ifTrue, MBasicBlock* ifFalse, MBasicBlock* existingPred) {
MInstruction* ins = block->lastIns();
if (ins->isTest()) {
MTest* test = ins->toTest();
MOZ_ASSERT(test->input() == value);
if (ifTrue != test->ifTrue()) {
test->ifTrue()->removePredecessor(block);
if (!ifTrue->addPredecessorSameInputsAs(block, existingPred)) {
return false;
}
MOZ_ASSERT(test->ifTrue() == test->getSuccessor(0));
test->replaceSuccessor(0, ifTrue);
}
if (ifFalse != test->ifFalse()) {
test->ifFalse()->removePredecessor(block);
if (!ifFalse->addPredecessorSameInputsAs(block, existingPred)) {
return false;
}
MOZ_ASSERT(test->ifFalse() == test->getSuccessor(1));
test->replaceSuccessor(1, ifFalse);
}
return true;
}
MOZ_ASSERT(ins->isGoto());
ins->toGoto()->target()->removePredecessor(block);
block->discardLastIns();
MTest* test = MTest::New(alloc, value, ifTrue, ifFalse);
block->end(test);
if (!ifTrue->addPredecessorSameInputsAs(block, existingPred)) {
return false;
}
if (!ifFalse->addPredecessorSameInputsAs(block, existingPred)) {
return false;
}
return true;
}
/*
* Look for a diamond pattern:
*
* initialBlock
* / \
* trueBranch falseBranch
* \ /
* phiBlock
* |
* testBlock
*/
static bool IsDiamondPattern(MBasicBlock* initialBlock) {
MInstruction* ins = initialBlock->lastIns();
if (!ins->isTest()) {
return false;
}
MTest* initialTest = ins->toTest();
MBasicBlock* trueBranch = initialTest->ifTrue();
if (trueBranch->numPredecessors() != 1 || !trueBranch->lastIns()->isGoto()) {
return false;
}
MBasicBlock* falseBranch = initialTest->ifFalse();
if (falseBranch->numPredecessors() != 1 ||
!falseBranch->lastIns()->isGoto()) {
return false;
}
MBasicBlock* phiBlock = trueBranch->getSuccessor(0);
if (phiBlock != falseBranch->getSuccessor(0)) {
return false;
}
if (phiBlock->numPredecessors() != 2) {
return false;
}
return true;
}
[[nodiscard]] static bool MaybeFoldDiamondConditionBlock(
MIRGraph& graph, MBasicBlock* initialBlock) {
MOZ_ASSERT(IsDiamondPattern(initialBlock));
// Optimize the MIR graph to improve the code generated for conditional
// operations. A test like 'if (a ? b : c)' normally requires four blocks,
// with a phi for the intermediate value. This can be improved to use three
// blocks with no phi value.
/*
* Look for a diamond pattern:
*
* initialBlock
* / \
* trueBranch falseBranch
* \ /
* phiBlock
* |
* testBlock
*
* Where phiBlock contains a single phi combining values pushed onto the
* stack by trueBranch and falseBranch, and testBlock contains a test on
* that phi. phiBlock and testBlock may be the same block; generated code
* will use different blocks if the (?:) op is in an inlined function.
*/
MTest* initialTest = initialBlock->lastIns()->toTest();
MBasicBlock* trueBranch = initialTest->ifTrue();
MBasicBlock* falseBranch = initialTest->ifFalse();
if (initialBlock->isLoopBackedge() || trueBranch->isLoopBackedge() ||
falseBranch->isLoopBackedge()) {
return true;
}
MBasicBlock* phiBlock = trueBranch->getSuccessor(0);
MBasicBlock* testBlock = phiBlock;
if (testBlock->numSuccessors() == 1) {
if (testBlock->isLoopBackedge()) {
return true;
}
testBlock = testBlock->getSuccessor(0);
if (testBlock->numPredecessors() != 1) {
return true;
}
}
MPhi* phi;
MTest* finalTest;
if (!BlockIsSingleTest(phiBlock, testBlock, &phi, &finalTest)) {
return true;
}
MOZ_ASSERT(phi->numOperands() == 2);
// Make sure the test block does not have any outgoing loop backedges.
if (!SplitCriticalEdgesForBlock(graph, testBlock)) {
return false;
}
MDefinition* trueResult =
phi->getOperand(phiBlock->indexForPredecessor(trueBranch));
MDefinition* falseResult =
phi->getOperand(phiBlock->indexForPredecessor(falseBranch));
// OK, we found the desired pattern, now transform the graph.
// Remove the phi from phiBlock.
phiBlock->discardPhi(*phiBlock->phisBegin());
// Change the end of the block to a test that jumps directly to successors of
// testBlock, rather than to testBlock itself.
if (IsTestInputMaybeToBool(initialTest, trueResult)) {
if (!UpdateGotoSuccessor(graph.alloc(), trueBranch, trueResult,
finalTest->ifTrue(), testBlock)) {
return false;
}
} else {
if (!UpdateTestSuccessors(graph.alloc(), trueBranch, trueResult,
finalTest->ifTrue(), finalTest->ifFalse(),
testBlock)) {
return false;
}
}
if (IsTestInputMaybeToBool(initialTest, falseResult)) {
if (!UpdateGotoSuccessor(graph.alloc(), falseBranch, falseResult,
finalTest->ifFalse(), testBlock)) {
return false;
}
} else {
if (!UpdateTestSuccessors(graph.alloc(), falseBranch, falseResult,
finalTest->ifTrue(), finalTest->ifFalse(),
testBlock)) {
return false;
}
}
// Remove phiBlock, if different from testBlock.
if (phiBlock != testBlock) {
testBlock->removePredecessor(phiBlock);
graph.removeBlock(phiBlock);
}
// Remove testBlock itself.
finalTest->ifTrue()->removePredecessor(testBlock);
finalTest->ifFalse()->removePredecessor(testBlock);
graph.removeBlock(testBlock);
return true;
}
/*
* Look for a triangle pattern:
*
* initialBlock
* / \
* trueBranch |
* \ /
* phiBlock+falseBranch
* |
* testBlock
*
* Or:
*
* initialBlock
* / \
* | falseBranch
* \ /
* phiBlock+trueBranch
* |
* testBlock
*/
static bool IsTrianglePattern(MBasicBlock* initialBlock) {
MInstruction* ins = initialBlock->lastIns();
if (!ins->isTest()) {
return false;
}
MTest* initialTest = ins->toTest();
MBasicBlock* trueBranch = initialTest->ifTrue();
MBasicBlock* falseBranch = initialTest->ifFalse();
if (trueBranch->numSuccessors() == 1 &&
trueBranch->getSuccessor(0) == falseBranch) {
if (trueBranch->numPredecessors() != 1) {
return false;
}
if (falseBranch->numPredecessors() != 2) {
return false;
}
return true;
}
if (falseBranch->numSuccessors() == 1 &&
falseBranch->getSuccessor(0) == trueBranch) {
if (trueBranch->numPredecessors() != 2) {
return false;
}
if (falseBranch->numPredecessors() != 1) {
return false;
}
return true;
}
return false;
}
[[nodiscard]] static bool MaybeFoldTriangleConditionBlock(
MIRGraph& graph, MBasicBlock* initialBlock) {
MOZ_ASSERT(IsTrianglePattern(initialBlock));
// Optimize the MIR graph to improve the code generated for boolean
// operations. A test like 'if (a && b)' normally requires three blocks, with
// a phi for the intermediate value. This can be improved to use no phi value.
/*
* Look for a triangle pattern:
*
* initialBlock
* / \
* trueBranch |
* \ /
* phiBlock+falseBranch
* |
* testBlock
*
* Or:
*
* initialBlock
* / \
* | falseBranch
* \ /
* phiBlock+trueBranch
* |
* testBlock
*
* Where phiBlock contains a single phi combining values pushed onto the stack
* by trueBranch and falseBranch, and testBlock contains a test on that phi.
* phiBlock and testBlock may be the same block; generated code will use
* different blocks if the (&&) op is in an inlined function.
*/
MTest* initialTest = initialBlock->lastIns()->toTest();
MBasicBlock* trueBranch = initialTest->ifTrue();
MBasicBlock* falseBranch = initialTest->ifFalse();
if (initialBlock->isLoopBackedge() || trueBranch->isLoopBackedge() ||
falseBranch->isLoopBackedge()) {
return true;
}
MBasicBlock* phiBlock;
if (trueBranch->numSuccessors() == 1 &&
trueBranch->getSuccessor(0) == falseBranch) {
phiBlock = falseBranch;
} else {
MOZ_ASSERT(falseBranch->getSuccessor(0) == trueBranch);
phiBlock = trueBranch;
}
MBasicBlock* testBlock = phiBlock;
if (testBlock->numSuccessors() == 1) {
MOZ_ASSERT(!testBlock->isLoopBackedge());
testBlock = testBlock->getSuccessor(0);
if (testBlock->numPredecessors() != 1) {
return true;
}
}
MPhi* phi;
MTest* finalTest;
if (!BlockIsSingleTest(phiBlock, testBlock, &phi, &finalTest)) {
return true;
}
MOZ_ASSERT(phi->numOperands() == 2);
// If the phi-operand doesn't match the initial input, we can't fold the test.
auto* phiInputForInitialBlock =
phi->getOperand(phiBlock->indexForPredecessor(initialBlock));
if (!IsTestInputMaybeToBool(initialTest, phiInputForInitialBlock)) {
return true;
}
// Make sure the test block does not have any outgoing loop backedges.
if (!SplitCriticalEdgesForBlock(graph, testBlock)) {
return false;
}
MDefinition* trueResult;
MDefinition* falseResult;
if (phiBlock == trueBranch) {
trueResult = phi->getOperand(phiBlock->indexForPredecessor(initialBlock));
falseResult = phi->getOperand(phiBlock->indexForPredecessor(falseBranch));
} else {
trueResult = phi->getOperand(phiBlock->indexForPredecessor(trueBranch));
falseResult = phi->getOperand(phiBlock->indexForPredecessor(initialBlock));
}
// OK, we found the desired pattern, now transform the graph.
// Remove the phi from phiBlock.
phiBlock->discardPhi(*phiBlock->phisBegin());
// Change the end of the block to a test that jumps directly to successors of
// testBlock, rather than to testBlock itself.
if (phiBlock == trueBranch) {
if (!UpdateTestSuccessors(graph.alloc(), initialBlock, initialTest->input(),
finalTest->ifTrue(), initialTest->ifFalse(),
testBlock)) {
return false;
}
} else if (IsTestInputMaybeToBool(initialTest, trueResult)) {
if (!UpdateGotoSuccessor(graph.alloc(), trueBranch, trueResult,
finalTest->ifTrue(), testBlock)) {
return false;
}
} else {
if (!UpdateTestSuccessors(graph.alloc(), trueBranch, trueResult,
finalTest->ifTrue(), finalTest->ifFalse(),
testBlock)) {
return false;
}
}
if (phiBlock == falseBranch) {
if (!UpdateTestSuccessors(graph.alloc(), initialBlock, initialTest->input(),
initialTest->ifTrue(), finalTest->ifFalse(),
testBlock)) {
return false;
}
} else if (IsTestInputMaybeToBool(initialTest, falseResult)) {
if (!UpdateGotoSuccessor(graph.alloc(), falseBranch, falseResult,
finalTest->ifFalse(), testBlock)) {
return false;
}
} else {
if (!UpdateTestSuccessors(graph.alloc(), falseBranch, falseResult,
finalTest->ifTrue(), finalTest->ifFalse(),
testBlock)) {
return false;
}
}
// Remove phiBlock, if different from testBlock.
if (phiBlock != testBlock) {
testBlock->removePredecessor(phiBlock);
graph.removeBlock(phiBlock);
}
// Remove testBlock itself.
finalTest->ifTrue()->removePredecessor(testBlock);
finalTest->ifFalse()->removePredecessor(testBlock);
graph.removeBlock(testBlock);
return true;
}
[[nodiscard]] static bool MaybeFoldConditionBlock(MIRGraph& graph,
MBasicBlock* initialBlock) {
if (IsDiamondPattern(initialBlock)) {
return MaybeFoldDiamondConditionBlock(graph, initialBlock);
}
if (IsTrianglePattern(initialBlock)) {
return MaybeFoldTriangleConditionBlock(graph, initialBlock);
}
return true;
}
[[nodiscard]] static bool MaybeFoldTestBlock(MIRGraph& graph,
MBasicBlock* initialBlock) {
// Handle test expressions on more than two inputs. For example
// |if ((x > 10) && (y > 20) && (z > 30)) { ... }|, which results in the below
// pattern.
//
// Look for the pattern:
// ┌─────────────────┐
// 1 │ 1 compare │
// ┌─────┤ 2 test compare1 │
// │ └──────┬──────────┘
// │ │0
// ┌───────▼─────────┐ │
// │ 3 compare │ │
// │ 4 test compare3 │ └──────────┐
// └──┬──────────┬───┘ │
// 1│ │0 │
// ┌──────────▼──────┐ │ │
// │ 5 compare │ └─────────┐ │
// │ 6 goto │ │ │
// └───────┬─────────┘ │ │
// │ │ │
// │ ┌──────────────────▼───────▼───────┐
// └───►│ 9 phi compare1 compare3 compare5 │
// │10 goto │
// └────────────────┬─────────────────┘
// │
// ┌────────▼────────┐
// │11 test phi9 │
// └─────┬─────┬─────┘
// 1│ │0
// ┌────────────┐ │ │ ┌─────────────┐
// │ TrueBranch │◄────┘ └─────►│ FalseBranch │
// └────────────┘ └─────────────┘
//
// And transform it to:
//
// ┌─────────────────┐
// 1 │ 1 compare │
// ┌───┤ 2 test compare1 │
// │ └──────────┬──────┘
// │ │0
// ┌───────▼─────────┐ │
// │ 3 compare │ │
// │ 4 test compare3 │ │
// └──┬─────────┬────┘ │
// 1│ │0 │
// ┌──────────▼──────┐ │ │
// │ 5 compare │ └──────┐ │
// │ 6 test compare5 │ │ │
// └────┬────────┬───┘ │ │
// 1│ │0 │ │
// ┌─────▼──────┐ │ ┌───▼──▼──────┐
// │ TrueBranch │ └─────────► FalseBranch │
// └────────────┘ └─────────────┘
auto* ins = initialBlock->lastIns();
if (!ins->isTest()) {
return true;
}
auto* initialTest = ins->toTest();
MBasicBlock* trueBranch = initialTest->ifTrue();
MBasicBlock* falseBranch = initialTest->ifFalse();
// MaybeFoldConditionBlock handles the case for two operands.
MBasicBlock* phiBlock;
if (trueBranch->numPredecessors() > 2) {
phiBlock = trueBranch;
} else if (falseBranch->numPredecessors() > 2) {
phiBlock = falseBranch;
} else {
return true;
}
MBasicBlock* testBlock = phiBlock;
if (testBlock->numSuccessors() == 1) {
if (testBlock->isLoopBackedge()) {
return true;
}
testBlock = testBlock->getSuccessor(0);
if (testBlock->numPredecessors() != 1) {
return true;
}
}
MOZ_ASSERT(!phiBlock->isLoopBackedge());
MPhi* phi = nullptr;
MTest* finalTest = nullptr;
if (!BlockIsSingleTest(phiBlock, testBlock, &phi, &finalTest)) {
return true;
}
MOZ_ASSERT(phiBlock->numPredecessors() == phi->numOperands());
// If the phi-operand doesn't match the initial input, we can't fold the test.
auto* phiInputForInitialBlock =
phi->getOperand(phiBlock->indexForPredecessor(initialBlock));
if (!IsTestInputMaybeToBool(initialTest, phiInputForInitialBlock)) {
return true;
}
MBasicBlock* newTestBlock = nullptr;
MDefinition* newTestInput = nullptr;
// The block of each phi operand must either end with a test instruction on
// that phi operand or it's the sole block which ends with a goto instruction.
for (size_t i = 0; i < phiBlock->numPredecessors(); i++) {
auto* pred = phiBlock->getPredecessor(i);
auto* operand = phi->getOperand(i);
// Each predecessor must end with either a test or goto instruction.
auto* lastIns = pred->lastIns();
if (lastIns->isGoto() && !newTestBlock) {
newTestBlock = pred;
newTestInput = operand;
} else if (lastIns->isTest()) {
if (!IsTestInputMaybeToBool(lastIns->toTest(), operand)) {
return true;
}
} else {
return true;
}
MOZ_ASSERT(!pred->isLoopBackedge());
}
// Ensure we found the single goto block.
if (!newTestBlock) {
return true;
}
// Make sure the test block does not have any outgoing loop backedges.
if (!SplitCriticalEdgesForBlock(graph, testBlock)) {
return false;
}
// OK, we found the desired pattern, now transform the graph.
// Remove the phi from phiBlock.
phiBlock->discardPhi(*phiBlock->phisBegin());
// Create the new test instruction.
if (!UpdateTestSuccessors(graph.alloc(), newTestBlock, newTestInput,
finalTest->ifTrue(), finalTest->ifFalse(),
testBlock)) {
return false;
}
// Update all test instructions to point to the final target.
while (phiBlock->numPredecessors()) {
mozilla::DebugOnly<size_t> oldNumPred = phiBlock->numPredecessors();
auto* pred = phiBlock->getPredecessor(0);
auto* test = pred->lastIns()->toTest();
if (test->ifTrue() == phiBlock) {
if (!UpdateTestSuccessors(graph.alloc(), pred, test->input(),
finalTest->ifTrue(), test->ifFalse(),
testBlock)) {
return false;
}
} else {
MOZ_ASSERT(test->ifFalse() == phiBlock);
if (!UpdateTestSuccessors(graph.alloc(), pred, test->input(),
test->ifTrue(), finalTest->ifFalse(),
testBlock)) {
return false;
}
}
// Ensure we've made progress.
MOZ_ASSERT(phiBlock->numPredecessors() + 1 == oldNumPred);
}
// Remove phiBlock, if different from testBlock.
if (phiBlock != testBlock) {
testBlock->removePredecessor(phiBlock);
graph.removeBlock(phiBlock);
}
// Remove testBlock itself.
finalTest->ifTrue()->removePredecessor(testBlock);
finalTest->ifFalse()->removePredecessor(testBlock);
graph.removeBlock(testBlock);
return true;
}
bool jit::FoldTests(MIRGraph& graph) {
for (PostorderIterator block(graph.poBegin()); block != graph.poEnd();
block++) {
if (!MaybeFoldConditionBlock(graph, *block)) {
return false;
}
if (!MaybeFoldTestBlock(graph, *block)) {
return false;
}
}
return true;
}
bool jit::FoldEmptyBlocks(MIRGraph& graph, bool* changed) {
*changed = false;
for (MBasicBlockIterator iter(graph.begin()); iter != graph.end();) {
MBasicBlock* block = *iter;
iter++;
if (block->numPredecessors() != 1 || block->numSuccessors() != 1) {
continue;
}
if (!block->phisEmpty()) {
continue;
}
if (block->outerResumePoint()) {
continue;
}
if (*block->begin() != *block->rbegin()) {
continue;
}
MBasicBlock* succ = block->getSuccessor(0);
MBasicBlock* pred = block->getPredecessor(0);
if (succ->numPredecessors() != 1) {
continue;
}
size_t pos = pred->getSuccessorIndex(block);
pred->lastIns()->replaceSuccessor(pos, succ);
graph.removeBlock(block);
if (!succ->addPredecessorSameInputsAs(pred, block)) {
return false;
}
succ->removePredecessor(block);
*changed = true;
}
return true;
}
static void EliminateTriviallyDeadResumePointOperands(MIRGraph& graph,
MResumePoint* rp) {
// If we will pop the top of the stack immediately after resuming,
// then don't preserve the top value in the resume point.
if (rp->mode() != ResumeMode::ResumeAt) {
return;
}
jsbytecode* pc = rp->pc();
if (JSOp(*pc) == JSOp::JumpTarget) {
pc += JSOpLength_JumpTarget;
}
if (JSOp(*pc) != JSOp::Pop) {
return;
}
size_t top = rp->stackDepth() - 1;
MOZ_ASSERT(!rp->isObservableOperand(top));
MDefinition* def = rp->getOperand(top);
if (def->isConstant()) {
return;
}
MConstant* constant = rp->block()->optimizedOutConstant(graph.alloc());
rp->replaceOperand(top, constant);
}
// Operands to a resume point which are dead at the point of the resume can be
// replaced with a magic value. This pass only replaces resume points which are
// trivially dead.
//
// This is intended to ensure that extra resume points within a basic block
// will not artificially extend the lifetimes of any SSA values. This could
// otherwise occur if the new resume point captured a value which is created
// between the old and new resume point and is dead at the new resume point.
bool jit::EliminateTriviallyDeadResumePointOperands(const MIRGenerator* mir,
MIRGraph& graph) {
for (auto* block : graph) {
if (MResumePoint* rp = block->entryResumePoint()) {
if (!graph.alloc().ensureBallast()) {
return false;
}
::EliminateTriviallyDeadResumePointOperands(graph, rp);
}
}
return true;
}
// Operands to a resume point which are dead at the point of the resume can be
// replaced with a magic value. This analysis supports limited detection of
// dead operands, pruning those which are defined in the resume point's basic
// block and have no uses outside the block or at points later than the resume
// point.
//
// This is intended to ensure that extra resume points within a basic block
// will not artificially extend the lifetimes of any SSA values. This could
// otherwise occur if the new resume point captured a value which is created
// between the old and new resume point and is dead at the new resume point.
bool jit::EliminateDeadResumePointOperands(const MIRGenerator* mir,
MIRGraph& graph) {
// If we are compiling try blocks, locals and arguments may be observable
// from catch or finally blocks (which Ion does not compile). For now just
// disable the pass in this case.
if (graph.hasTryBlock()) {
return true;
}
for (PostorderIterator block = graph.poBegin(); block != graph.poEnd();
block++) {
if (mir->shouldCancel("Eliminate Dead Resume Point Operands (main loop)")) {
return false;
}
if (MResumePoint* rp = block->entryResumePoint()) {
if (!graph.alloc().ensureBallast()) {
return false;
}
::EliminateTriviallyDeadResumePointOperands(graph, rp);
}
// The logic below can get confused on infinite loops.
if (block->isLoopHeader() && block->backedge() == *block) {
continue;
}
for (MInstructionIterator ins = block->begin(); ins != block->end();
ins++) {
if (MResumePoint* rp = ins->resumePoint()) {
if (!graph.alloc().ensureBallast()) {
return false;
}
::EliminateTriviallyDeadResumePointOperands(graph, rp);
}
// No benefit to replacing constant operands with other constants.
if (ins->isConstant()) {
continue;
}
// Scanning uses does not give us sufficient information to tell
// where instructions that are involved in box/unbox operations or
// parameter passing might be live. Rewriting uses of these terms
// in resume points may affect the interpreter's behavior. Rather
// than doing a more sophisticated analysis, just ignore these.
if (ins->isUnbox() || ins->isParameter() || ins->isBoxNonStrictThis()) {
continue;
}
// Early intermediate values captured by resume points, such as
// ArrayState and its allocation, may be legitimately dead in Ion code,
// but are still needed if we bail out. They can recover on bailout.
if (ins->isRecoveredOnBailout()) {
MOZ_ASSERT(ins->canRecoverOnBailout());
continue;
}
// If the instruction's behavior has been constant folded into a
// separate instruction, we can't determine precisely where the
// instruction becomes dead and can't eliminate its uses.
if (ins->isImplicitlyUsed()) {
continue;
}
// Check if this instruction's result is only used within the
// current block, and keep track of its last use in a definition
// (not resume point). This requires the instructions in the block
// to be numbered, ensured by running this immediately after alias
// analysis.
uint32_t maxDefinition = 0;
for (MUseIterator uses(ins->usesBegin()); uses != ins->usesEnd();
uses++) {
MNode* consumer = uses->consumer();
if (consumer->isResumePoint()) {
// If the instruction's is captured by one of the resume point, then
// it might be observed indirectly while the frame is live on the
// stack, so it has to be computed.
MResumePoint* resume = consumer->toResumePoint();
if (resume->isObservableOperand(*uses)) {
maxDefinition = UINT32_MAX;
break;
}
continue;
}
MDefinition* def = consumer->toDefinition();
if (def->block() != *block || def->isBox() || def->isPhi()) {
maxDefinition = UINT32_MAX;
break;
}
maxDefinition = std::max(maxDefinition, def->id());
}
if (maxDefinition == UINT32_MAX) {
continue;
}
// Walk the uses a second time, removing any in resume points after
// the last use in a definition.
for (MUseIterator uses(ins->usesBegin()); uses != ins->usesEnd();) {
MUse* use = *uses++;
if (use->consumer()->isDefinition()) {
continue;
}
MResumePoint* mrp = use->consumer()->toResumePoint();
if (mrp->block() != *block || !mrp->instruction() ||
mrp->instruction() == *ins ||
mrp->instruction()->id() <= maxDefinition) {
continue;
}
if (!graph.alloc().ensureBallast()) {
return false;
}
// Store an optimized out magic value in place of all dead
// resume point operands. Making any such substitution can in
// general alter the interpreter's behavior, even though the
// code is dead, as the interpreter will still execute opcodes
// whose effects cannot be observed. If the magic value value
// were to flow to, say, a dead property access the
// interpreter could throw an exception; we avoid this problem
// by removing dead operands before removing dead code.
MConstant* constant =
MConstant::New(graph.alloc(), MagicValue(JS_OPTIMIZED_OUT));
block->insertBefore(*(block->begin()), constant);
use->replaceProducer(constant);
}
}
}
return true;
}
// Test whether |def| would be needed if it had no uses.
bool js::jit::DeadIfUnused(const MDefinition* def) {
// Effectful instructions of course cannot be removed.
if (def->isEffectful()) {
return false;
}
// Never eliminate guard instructions.
if (def->isGuard()) {
return false;
}
// Required to be preserved, as the type guard related to this instruction
// is part of the semantics of a transformation.
if (def->isGuardRangeBailouts()) {
return false;
}
// Control instructions have no uses, but also shouldn't be optimized out
if (def->isControlInstruction()) {
return false;
}
// Used when lowering to generate the corresponding snapshots and aggregate
// the list of recover instructions to be repeated.
if (def->isInstruction() && def->toInstruction()->resumePoint()) {
return false;
}
return true;
}
// Similar to DeadIfUnused(), but additionally allows effectful instructions.
bool js::jit::DeadIfUnusedAllowEffectful(const MDefinition* def) {
// Never eliminate guard instructions.
if (def->isGuard()) {
return false;
}
// Required to be preserved, as the type guard related to this instruction
// is part of the semantics of a transformation.
if (def->isGuardRangeBailouts()) {
return false;
}
// Control instructions have no uses, but also shouldn't be optimized out
if (def->isControlInstruction()) {
return false;
}
// Used when lowering to generate the corresponding snapshots and aggregate
// the list of recover instructions to be repeated.
if (def->isInstruction() && def->toInstruction()->resumePoint()) {
// All effectful instructions must have a resume point attached. We're
// allowing effectful instructions here, so we have to ignore any resume
// points if we want to consider effectful instructions as dead.
if (!def->isEffectful()) {
return false;
}
}
return true;
}
// Test whether |def| may be safely discarded, due to being dead or due to being
// located in a basic block which has itself been marked for discarding.
bool js::jit::IsDiscardable(const MDefinition* def) {
return !def->hasUses() && (DeadIfUnused(def) || def->block()->isMarked());
}
// Similar to IsDiscardable(), but additionally allows effectful instructions.
bool js::jit::IsDiscardableAllowEffectful(const MDefinition* def) {
return !def->hasUses() &&
(DeadIfUnusedAllowEffectful(def) || def->block()->isMarked());
}
// Instructions are useless if they are unused and have no side effects.
// This pass eliminates useless instructions.
// The graph itself is unchanged.
bool jit::EliminateDeadCode(const MIRGenerator* mir, MIRGraph& graph) {
// Traverse in postorder so that we hit uses before definitions.
// Traverse instruction list backwards for the same reason.
for (PostorderIterator block = graph.poBegin(); block != graph.poEnd();
block++) {
if (mir->shouldCancel("Eliminate Dead Code (main loop)")) {
return false;
}
// Remove unused instructions.
for (MInstructionReverseIterator iter = block->rbegin();
iter != block->rend();) {
MInstruction* inst = *iter++;
if (js::jit::IsDiscardable(inst)) {
block->discard(inst);
}
}
}
return true;
}
static inline bool IsPhiObservable(MPhi* phi, Observability observe) {
// If the phi has uses which are not reflected in SSA, then behavior in the
// interpreter may be affected by removing the phi.
if (phi->isImplicitlyUsed()) {
return true;
}
// Check for uses of this phi node outside of other phi nodes.
// Note that, initially, we skip reading resume points, which we
// don't count as actual uses. If the only uses are resume points,
// then the SSA name is never consumed by the program. However,
// after optimizations have been performed, it's possible that the
// actual uses in the program have been (incorrectly) optimized
// away, so we must be more conservative and consider resume
// points as well.
for (MUseIterator iter(phi->usesBegin()); iter != phi->usesEnd(); iter++) {
MNode* consumer = iter->consumer();
if (consumer->isResumePoint()) {
MResumePoint* resume = consumer->toResumePoint();
if (observe == ConservativeObservability) {
return true;
}
if (resume->isObservableOperand(*iter)) {
return true;
}
} else {
MDefinition* def = consumer->toDefinition();
if (!def->isPhi()) {
return true;
}
}
}
return false;
}
// Handles cases like:
// x is phi(a, x) --> a
// x is phi(a, a) --> a
static inline MDefinition* IsPhiRedundant(MPhi* phi) {
MDefinition* first = phi->operandIfRedundant();
if (first == nullptr) {
return nullptr;
}
// Propagate the ImplicitlyUsed flag if |phi| is replaced with another phi.
if (phi->isImplicitlyUsed()) {
first->setImplicitlyUsedUnchecked();
}
return first;
}
bool jit::EliminatePhis(const MIRGenerator* mir, MIRGraph& graph,
Observability observe) {
// Eliminates redundant or unobservable phis from the graph. A
// redundant phi is something like b = phi(a, a) or b = phi(a, b),
// both of which can be replaced with a. An unobservable phi is
// one that whose value is never used in the program.
//
// Note that we must be careful not to eliminate phis representing
// values that the interpreter will require later. When the graph
// is first constructed, we can be more aggressive, because there
// is a greater correspondence between the CFG and the bytecode.
// After optimizations such as GVN have been performed, however,
// the bytecode and CFG may not correspond as closely to one
// another. In that case, we must be more conservative. The flag
// |conservativeObservability| is used to indicate that eliminate
// phis is being run after some optimizations have been performed,
// and thus we should use more conservative rules about
// observability. The particular danger is that we can optimize
// away uses of a phi because we think they are not executable,
// but the foundation for that assumption is false TI information
// that will eventually be invalidated. Therefore, if
// |conservativeObservability| is set, we will consider any use
// from a resume point to be observable. Otherwise, we demand a
// use from an actual instruction.
Vector<MPhi*, 16, SystemAllocPolicy> worklist;
// Add all observable phis to a worklist. We use the "in worklist" bit to
// mean "this phi is live".
for (PostorderIterator block = graph.poBegin(); block != graph.poEnd();
block++) {
MPhiIterator iter = block->phisBegin();
while (iter != block->phisEnd()) {
MPhi* phi = *iter++;
if (mir->shouldCancel("Eliminate Phis (populate loop)")) {
return false;
}
// Flag all as unused, only observable phis would be marked as used
// when processed by the work list.
phi->setUnused();
// If the phi is redundant, remove it here.
if (MDefinition* redundant = IsPhiRedundant(phi)) {
phi->justReplaceAllUsesWith(redundant);
block->discardPhi(phi);
continue;
}
// Enqueue observable Phis.
if (IsPhiObservable(phi, observe)) {
phi->setInWorklist();
if (!worklist.append(phi)) {
return false;
}
}
}
}
// Iteratively mark all phis reachable from live phis.
while (!worklist.empty()) {
if (mir->shouldCancel("Eliminate Phis (worklist)")) {
return false;
}
MPhi* phi = worklist.popCopy();
MOZ_ASSERT(phi->isUnused());
phi->setNotInWorklist();
// The removal of Phis can produce newly redundant phis.
if (MDefinition* redundant = IsPhiRedundant(phi)) {
// Add to the worklist the used phis which are impacted.
for (MUseDefIterator it(phi); it; it++) {
if (it.def()->isPhi()) {
MPhi* use = it.def()->toPhi();
if (!use->isUnused()) {
use->setUnusedUnchecked();
use->setInWorklist();
if (!worklist.append(use)) {
return false;
}
}
}
}
phi->justReplaceAllUsesWith(redundant);
} else {
// Otherwise flag them as used.
phi->setNotUnused();
}
// The current phi is/was used, so all its operands are used.
for (size_t i = 0, e = phi->numOperands(); i < e; i++) {
MDefinition* in = phi->getOperand(i);
if (!in->isPhi() || !in->isUnused() || in->isInWorklist()) {
continue;
}
in->setInWorklist();
if (!worklist.append(in->toPhi())) {
return false;
}
}
}
// Sweep dead phis.
for (PostorderIterator block = graph.poBegin(); block != graph.poEnd();
block++) {
if (mir->shouldCancel("Eliminate Phis (sweep dead phis)")) {
return false;
}
MPhiIterator iter = block->phisBegin();
while (iter != block->phisEnd()) {
MPhi* phi = *iter++;
if (phi->isUnused()) {
if (!phi->optimizeOutAllUses(graph.alloc())) {
return false;
}
block->discardPhi(phi);
}
}
}
return true;
}
namespace {
// The type analysis algorithm inserts conversions and box/unbox instructions
// to make the IR graph well-typed for future passes.
//
// Phi adjustment: If a phi's inputs are all the same type, the phi is
// specialized to return that type.
//
// Input adjustment: Each input is asked to apply conversion operations to its
// inputs. This may include Box, Unbox, or other instruction-specific type
// conversion operations.
//
class TypeAnalyzer {
const MIRGenerator* mir;
MIRGraph& graph;
Vector<MPhi*, 0, SystemAllocPolicy> phiWorklist_;
TempAllocator& alloc() const { return graph.alloc(); }
bool addPhiToWorklist(MPhi* phi) {
if (phi->isInWorklist()) {
return true;
}
if (!phiWorklist_.append(phi)) {
return false;
}
phi->setInWorklist();
return true;
}
MPhi* popPhi() {
MPhi* phi = phiWorklist_.popCopy();
phi->setNotInWorklist();
return phi;
}
[[nodiscard]] bool propagateAllPhiSpecializations();
bool respecialize(MPhi* phi, MIRType type);
bool propagateSpecialization(MPhi* phi);
bool specializePhis();
bool specializeOsrOnlyPhis();
void replaceRedundantPhi(MPhi* phi);
bool adjustPhiInputs(MPhi* phi);
bool adjustInputs(MDefinition* def);
bool insertConversions();
bool checkFloatCoherency();
bool graphContainsFloat32();
bool markPhiConsumers();
bool markPhiProducers();
bool specializeValidFloatOps();
bool tryEmitFloatOperations();
bool propagateUnbox();
bool shouldSpecializeOsrPhis() const;
MIRType guessPhiType(MPhi* phi) const;
public:
TypeAnalyzer(const MIRGenerator* mir, MIRGraph& graph)
: mir(mir), graph(graph) {}
bool analyze();
};
} /* anonymous namespace */
bool TypeAnalyzer::shouldSpecializeOsrPhis() const {
// [SMDOC] OSR Phi Type Specialization
//
// Without special handling for OSR phis, we end up with unspecialized phis
// (MIRType::Value) in the loop (pre)header and other blocks, resulting in
// unnecessary boxing and unboxing in the loop body.
//
// To fix this, phi type specialization needs special code to deal with the
// OSR entry block. Recall that OSR results in the following basic block
// structure:
//
// +------------------+ +-----------------+
// | Code before loop | | OSR entry block |
// +------------------+ +-----------------+
// | |
// | |
// | +---------------+ |
// +---------> | OSR preheader | <---------+
// +---------------+
// |
// V
// +---------------+
// | Loop header |<-----+
// +---------------+ |
// | |
// ... |
// | |
// +---------------+ |
// | Loop backedge |------+
// +---------------+
//
// OSR phi specialization happens in three steps:
//
// (1) Specialize phis but ignore MOsrValue phi inputs. In other words,
// pretend the OSR entry block doesn't exist. See guessPhiType.
//
// (2) Once phi specialization is done, look at the types of loop header phis
// and add these types to the corresponding preheader phis. This way, the
// types of the preheader phis are based on the code before the loop and
// the code in the loop body. These are exactly the types we expect for
// the OSR Values. See the last part of TypeAnalyzer::specializePhis.
//
// (3) For type-specialized preheader phis, add guard/unbox instructions to
// the OSR entry block to guard the incoming Value indeed has this type.
// This happens in:
//
// * TypeAnalyzer::adjustPhiInputs: adds a fallible unbox for values that
// can be unboxed.
//
// * TypeAnalyzer::replaceRedundantPhi: adds a type guard for values that
// can't be unboxed (null/undefined/magic Values).
if (!graph.osrBlock()) {
return false;
}
return !mir->outerInfo().hadSpeculativePhiBailout();
}
// Try to specialize this phi based on its non-cyclic inputs.
MIRType TypeAnalyzer::guessPhiType(MPhi* phi) const {
#ifdef DEBUG
// Check that different magic constants aren't flowing together. Ignore
// JS_OPTIMIZED_OUT, since an operand could be legitimately optimized
// away.
MIRType magicType = MIRType::None;
for (size_t i = 0; i < phi->numOperands(); i++) {
MDefinition* in = phi->getOperand(i);
if (in->type() == MIRType::MagicHole ||
in->type() == MIRType::MagicIsConstructing) {
if (magicType == MIRType::None) {
magicType = in->type();
}
MOZ_ASSERT(magicType == in->type());
}
}
#endif
MIRType type = MIRType::None;
bool convertibleToFloat32 = false;
bool hasOSRValueInput = false;
DebugOnly<bool> hasSpecializableInput = false;
for (size_t i = 0, e = phi->numOperands(); i < e; i++) {
MDefinition* in = phi->getOperand(i);
if (in->isPhi()) {
hasSpecializableInput = true;
if (!in->toPhi()->triedToSpecialize()) {
continue;
}
if (in->type() == MIRType::None) {
// The operand is a phi we tried to specialize, but we were
// unable to guess its type. propagateSpecialization will
// propagate the type to this phi when it becomes known.
continue;
}
}
// See shouldSpecializeOsrPhis comment. This is the first step mentioned
// there.
if (shouldSpecializeOsrPhis() && in->isOsrValue()) {
hasOSRValueInput = true;
hasSpecializableInput = true;
continue;
}
if (type == MIRType::None) {
type = in->type();
if (in->canProduceFloat32() &&
!mir->outerInfo().hadSpeculativePhiBailout()) {
convertibleToFloat32 = true;
}
continue;
}
if (type == in->type()) {
convertibleToFloat32 = convertibleToFloat32 && in->canProduceFloat32();
} else {
if (convertibleToFloat32 && in->type() == MIRType::Float32) {
// If we only saw definitions that can be converted into Float32 before
// and encounter a Float32 value, promote previous values to Float32
type = MIRType::Float32;
} else if (IsTypeRepresentableAsDouble(type) &&
IsTypeRepresentableAsDouble(in->type())) {
// Specialize phis with int32 and double operands as double.
type = MIRType::Double;
convertibleToFloat32 = convertibleToFloat32 && in->canProduceFloat32();
} else {
return MIRType::Value;
}
}
}
if (hasOSRValueInput && type == MIRType::Float32) {
// TODO(post-Warp): simplify float32 handling in this function or (better)
// make the float32 analysis a stand-alone optimization pass instead of
type = MIRType::Double;
}
MOZ_ASSERT_IF(type == MIRType::None, hasSpecializableInput);
return type;
}
bool TypeAnalyzer::respecialize(MPhi* phi, MIRType type) {
if (phi->type() == type) {
return true;
}
phi->specialize(type);
return addPhiToWorklist(phi);
}
bool TypeAnalyzer::propagateSpecialization(MPhi* phi) {
MOZ_ASSERT(phi->type() != MIRType::None);
// Verify that this specialization matches any phis depending on it.
for (MUseDefIterator iter(phi); iter; iter++) {
if (!iter.def()->isPhi()) {
continue;
}
MPhi* use = iter.def()->toPhi();
if (!use->triedToSpecialize()) {
continue;
}
if (use->type() == MIRType::None) {
// We tried to specialize this phi, but were unable to guess its
// type. Now that we know the type of one of its operands, we can
// specialize it. If it can't be specialized as float32, specialize
// as double.
MIRType type = phi->type();
if (type == MIRType::Float32 && !use->canProduceFloat32()) {
type = MIRType::Double;
}
if (!respecialize(use, type)) {
return false;
}
continue;
}
if (use->type() != phi->type()) {
// Specialize phis with int32 that can be converted to float and float
// operands as floats.
if ((use->type() == MIRType::Int32 && use->canProduceFloat32() &&
phi->type() == MIRType::Float32) ||
(phi->type() == MIRType::Int32 && phi->canProduceFloat32() &&
use->type() == MIRType::Float32)) {
if (!respecialize(use, MIRType::Float32)) {
return false;
}
continue;
}
// Specialize phis with int32 and double operands as double.
if (IsTypeRepresentableAsDouble(use->type()) &&
IsTypeRepresentableAsDouble(phi->type())) {
if (!respecialize(use, MIRType::Double)) {
return false;
}
continue;
}
// This phi in our use chain can now no longer be specialized.
if (!respecialize(use, MIRType::Value)) {
return false;
}
}
}
return true;
}
bool TypeAnalyzer::propagateAllPhiSpecializations() {
while (!phiWorklist_.empty()) {
if (mir->shouldCancel("Specialize Phis (worklist)")) {
return false;
}
MPhi* phi = popPhi();
if (!propagateSpecialization(phi)) {
return false;
}
}
return true;
}
// If branch pruning removes the path from the entry block to the OSR
// preheader, we may have phis (or chains of phis) with no operands
// other than OsrValues. These phis will still have MIRType::None.
// Since we don't have any information about them, we specialize them
// as MIRType::Value.
bool TypeAnalyzer::specializeOsrOnlyPhis() {
MOZ_ASSERT(graph.osrBlock());
MOZ_ASSERT(graph.osrPreHeaderBlock()->numPredecessors() == 1);
for (PostorderIterator block(graph.poBegin()); block != graph.poEnd();
block++) {
if (mir->shouldCancel("Specialize osr-only phis (main loop)")) {
return false;
}
for (MPhiIterator phi(block->phisBegin()); phi != block->phisEnd(); phi++) {
if (mir->shouldCancel("Specialize osr-only phis (inner loop)")) {
return false;
}
if (phi->type() == MIRType::None) {
phi->specialize(MIRType::Value);
}
}
}
return true;
}
bool TypeAnalyzer::specializePhis() {
for (PostorderIterator block(graph.poBegin()); block != graph.poEnd();
block++) {
if (mir->shouldCancel("Specialize Phis (main loop)")) {
return false;
}
for (MPhiIterator phi(block->phisBegin()); phi != block->phisEnd(); phi++) {
if (mir->shouldCancel("Specialize Phis (inner loop)")) {
return false;
}
MIRType type = guessPhiType(*phi);
phi->specialize(type);
if (type == MIRType::None) {
// We tried to guess the type but failed because all operands are
// phis we still have to visit. Set the triedToSpecialize flag but
// don't propagate the type to other phis, propagateSpecialization
// will do that once we know the type of one of the operands.
continue;
}
if (!propagateSpecialization(*phi)) {
return false;
}
}
}
if (!propagateAllPhiSpecializations()) {
return false;
}
if (shouldSpecializeOsrPhis()) {
// See shouldSpecializeOsrPhis comment. This is the second step, propagating
// loop header phi types to preheader phis.
MBasicBlock* preHeader = graph.osrPreHeaderBlock();
MBasicBlock* header = preHeader->getSingleSuccessor();
if (preHeader->numPredecessors() == 1) {
MOZ_ASSERT(preHeader->getPredecessor(0) == graph.osrBlock());
// Branch pruning has removed the path from the entry block
// to the preheader. Specialize any phis with no non-osr inputs.
if (!specializeOsrOnlyPhis()) {
return false;
}
} else if (header->isLoopHeader()) {
for (MPhiIterator phi(header->phisBegin()); phi != header->phisEnd();
phi++) {
MPhi* preHeaderPhi = phi->getOperand(0)->toPhi();
MOZ_ASSERT(preHeaderPhi->block() == preHeader);
if (preHeaderPhi->type() == MIRType::Value) {
// Already includes everything.
continue;
}
MIRType loopType = phi->type();
if (!respecialize(preHeaderPhi, loopType)) {
return false;
}
}
if (!propagateAllPhiSpecializations()) {
return false;
}
} else {
// Edge case: there is no backedge in this loop. This can happen
// if the header is a 'pending' loop header when control flow in
// the loop body is terminated unconditionally, or if a block
// that dominates the backedge unconditionally bails out. In
// this case the header only has the preheader as predecessor
// and we don't need to do anything.
MOZ_ASSERT(header->numPredecessors() == 1);
}
}
MOZ_ASSERT(phiWorklist_.empty());
return true;
}
bool TypeAnalyzer::adjustPhiInputs(MPhi* phi) {
MIRType phiType = phi->type();
MOZ_ASSERT(phiType != MIRType::None);
// If we specialized a type that's not Value, there are 3 cases:
// 1. Every input is of that type.
// 2. Every observed input is of that type (i.e., some inputs haven't been
// executed yet).
// 3. Inputs were numbers, and was specialized to floating point type.
if (phiType != MIRType::Value) {
for (size_t i = 0, e = phi->numOperands(); i < e; i++) {
MDefinition* in = phi->getOperand(i);
if (in->type() == phiType) {
continue;
}
if (in->isBox() && in->toBox()->input()->type() == phiType) {
phi->replaceOperand(i, in->toBox()->input());
continue;
}
if (!alloc().ensureBallast()) {
return false;
}
MBasicBlock* predecessor = phi->block()->getPredecessor(i);
MInstruction* replacement;
if (IsFloatingPointType(phiType) &&
IsTypeRepresentableAsDouble(in->type())) {
// Convert number operands to |phiType|.
if (phiType == MIRType::Double) {
replacement = MToDouble::New(alloc(), in);
} else {
MOZ_ASSERT(phiType == MIRType::Float32);
replacement = MToFloat32::New(alloc(), in);
}
} else {
// If we know this branch will fail to convert to phiType, insert a box
// that'll immediately fail in the fallible unbox below.
if (in->type() != MIRType::Value) {
auto* box = MBox::New(alloc(), in);
predecessor->insertAtEnd(box);
in = box;
}
// Be optimistic and insert unboxes when the operand is a value.
if (phiType == MIRType::Float32) {
// Float32 is unboxed as Double, then converted.
auto* unbox =
MUnbox::New(alloc(), in, MIRType::Double, MUnbox::Fallible);
unbox->setBailoutKind(BailoutKind::SpeculativePhi);
predecessor->insertAtEnd(unbox);
replacement = MToFloat32::New(alloc(), unbox);
} else {
replacement = MUnbox::New(alloc(), in, phiType, MUnbox::Fallible);
replacement->setBailoutKind(BailoutKind::SpeculativePhi);
}
}
MOZ_ASSERT(replacement->type() == phiType);
predecessor->insertAtEnd(replacement);
phi->replaceOperand(i, replacement);
}
return true;
}
// Box every typed input.
for (size_t i = 0, e = phi->numOperands(); i < e; i++) {
MDefinition* in = phi->getOperand(i);
if (in->type() == MIRType::Value) {
continue;
}
// The input is being explicitly unboxed, so sneak past and grab the
// original box. Don't bother optimizing if magic values are involved.
if (in->isUnbox()) {
MDefinition* unboxInput = in->toUnbox()->input();
if (!IsMagicType(unboxInput->type()) && phi->typeIncludes(unboxInput)) {
in = in->toUnbox()->input();
}
}
if (in->type() != MIRType::Value) {
if (!alloc().ensureBallast()) {
return false;
}
MBasicBlock* pred = phi->block()->getPredecessor(i);
in = BoxAt(alloc(), pred->lastIns(), in);
}
phi->replaceOperand(i, in);
}
return true;
}
bool TypeAnalyzer::adjustInputs(MDefinition* def) {
// Definitions such as MPhi have no type policy.
if (!def->isInstruction()) {
return true;
}
MInstruction* ins = def->toInstruction();
const TypePolicy* policy = ins->typePolicy();
if (policy && !policy->adjustInputs(alloc(), ins)) {
return false;
}
return true;
}
void TypeAnalyzer::replaceRedundantPhi(MPhi* phi) {
MBasicBlock* block = phi->block();
js::Value v;
switch (phi->type()) {
case MIRType::Undefined:
v = UndefinedValue();
break;
case MIRType::Null:
v = NullValue();
break;
case MIRType::MagicOptimizedOut:
v = MagicValue(JS_OPTIMIZED_OUT);
break;
case MIRType::MagicUninitializedLexical:
v = MagicValue(JS_UNINITIALIZED_LEXICAL);
break;
case MIRType::MagicIsConstructing:
v = MagicValue(JS_IS_CONSTRUCTING);
break;
case MIRType::MagicHole:
default:
MOZ_CRASH("unexpected type");
}
MConstant* c = MConstant::New(alloc(), v);
// The instruction pass will insert the box
block->insertBefore(*(block->begin()), c);
phi->justReplaceAllUsesWith(c);
if (shouldSpecializeOsrPhis()) {
// See shouldSpecializeOsrPhis comment. This is part of the third step,
// guard the incoming MOsrValue is of this type.
for (uint32_t i = 0; i < phi->numOperands(); i++) {
MDefinition* def = phi->getOperand(i);
if (def->type() != phi->type()) {
MOZ_ASSERT(def->isOsrValue() || def->isPhi());
MOZ_ASSERT(def->type() == MIRType::Value);
MGuardValue* guard = MGuardValue::New(alloc(), def, v);
guard->setBailoutKind(BailoutKind::SpeculativePhi);
def->block()->insertBefore(def->block()->lastIns(), guard);
}
}
}
}
bool TypeAnalyzer::insertConversions() {
// Instructions are processed in reverse postorder: all uses are defs are
// seen before uses. This ensures that output adjustment (which may rewrite
// inputs of uses) does not conflict with input adjustment.
for (ReversePostorderIterator block(graph.rpoBegin());
block != graph.rpoEnd(); block++) {
if (mir->shouldCancel("Insert Conversions")) {
return false;
}
for (MPhiIterator iter(block->phisBegin()), end(block->phisEnd());
iter != end;) {
MPhi* phi = *iter++;
if (IsNullOrUndefined(phi->type()) || IsMagicType(phi->type())) {
// We can replace this phi with a constant.
if (!alloc().ensureBallast()) {
return false;
}
replaceRedundantPhi(phi);
block->discardPhi(phi);
} else {
if (!adjustPhiInputs(phi)) {
return false;
}
}
}
// AdjustInputs can add/remove/mutate instructions before and after the
// current instruction. Only increment the iterator after it is finished.
for (MInstructionIterator iter(block->begin()); iter != block->end();
iter++) {
if (!alloc().ensureBallast()) {
return false;
}
if (!adjustInputs(*iter)) {
return false;
}
}
}
return true;
}
/* clang-format off */
//
// This function tries to emit Float32 specialized operations whenever it's possible.
// MIR nodes are flagged as:
// - Producers, when they can create Float32 that might need to be coerced into a Double.
// Loads in Float32 arrays and conversions to Float32 are producers.
// - Consumers, when they can have Float32 as inputs and validate a legal use of a Float32.
// Stores in Float32 arrays and conversions to Float32 are consumers.
// - Float32 commutative, when using the Float32 instruction instead of the Double instruction
// does not result in a compound loss of precision. This is the case for +, -, /, * with 2
// operands, for instance. However, an addition with 3 operands is not commutative anymore,
// so an intermediate coercion is needed.
// Except for phis, all these flags are known after Ion building, so they cannot change during
// the process.
//
// The idea behind the algorithm is easy: whenever we can prove that a commutative operation
// has only producers as inputs and consumers as uses, we can specialize the operation as a
// float32 operation. Otherwise, we have to convert all float32 inputs to doubles. Even
// if a lot of conversions are produced, GVN will take care of eliminating the redundant ones.
//
// Phis have a special status. Phis need to be flagged as producers or consumers as they can
// be inputs or outputs of commutative instructions. Fortunately, producers and consumers
// properties are such that we can deduce the property using all non phis inputs first (which form
// an initial phi graph) and then propagate all properties from one phi to another using a
// fixed point algorithm. The algorithm is ensured to terminate as each iteration has less or as
// many flagged phis as the previous iteration (so the worst steady state case is all phis being
// flagged as false).
//
// In a nutshell, the algorithm applies three passes:
// 1 - Determine which phis are consumers. Each phi gets an initial value by making a global AND on
// all its non-phi inputs. Then each phi propagates its value to other phis. If after propagation,
// the flag value changed, we have to reapply the algorithm on all phi operands, as a phi is a
// consumer if all of its uses are consumers.
// 2 - Determine which phis are producers. It's the same algorithm, except that we have to reapply
// the algorithm on all phi uses, as a phi is a producer if all of its operands are producers.
// 3 - Go through all commutative operations and ensure their inputs are all producers and their
// uses are all consumers.
//
/* clang-format on */
bool TypeAnalyzer::markPhiConsumers() {
MOZ_ASSERT(phiWorklist_.empty());
// Iterate in postorder so worklist is initialized to RPO.
for (PostorderIterator block(graph.poBegin()); block != graph.poEnd();
++block) {
if (mir->shouldCancel(
"Ensure Float32 commutativity - Consumer Phis - Initial state")) {
return false;
}
for (MPhiIterator phi(block->phisBegin()); phi != block->phisEnd(); ++phi) {
MOZ_ASSERT(!phi->isInWorklist());
bool canConsumeFloat32 = !phi->isImplicitlyUsed();
for (MUseDefIterator use(*phi); canConsumeFloat32 && use; use++) {
MDefinition* usedef = use.def();
canConsumeFloat32 &=
usedef->isPhi() || usedef->canConsumeFloat32(use.use());
}
phi->setCanConsumeFloat32(canConsumeFloat32);
if (canConsumeFloat32 && !addPhiToWorklist(*phi)) {
return false;
}
}
}
while (!phiWorklist_.empty()) {
if (mir->shouldCancel(
"Ensure Float32 commutativity - Consumer Phis - Fixed point")) {
return false;
}
MPhi* phi = popPhi();
MOZ_ASSERT(phi->canConsumeFloat32(nullptr /* unused */));
bool validConsumer = true;
for (MUseDefIterator use(phi); use; use++) {
MDefinition* def = use.def();
if (def->isPhi() && !def->canConsumeFloat32(use.use())) {
validConsumer = false;
break;
}
}
if (validConsumer) {
continue;
}
// Propagate invalidated phis
phi->setCanConsumeFloat32(false);
for (size_t i = 0, e = phi->numOperands(); i < e; ++i) {
MDefinition* input = phi->getOperand(i);
if (input->isPhi() && !input->isInWorklist() &&
input->canConsumeFloat32(nullptr /* unused */)) {
if (!addPhiToWorklist(input->toPhi())) {
return false;
}
}
}
}
return true;
}
bool TypeAnalyzer::markPhiProducers() {
MOZ_ASSERT(phiWorklist_.empty());
// Iterate in reverse postorder so worklist is initialized to PO.
for (ReversePostorderIterator block(graph.rpoBegin());
block != graph.rpoEnd(); ++block) {
if (mir->shouldCancel(
"Ensure Float32 commutativity - Producer Phis - initial state")) {
return false;
}
for (MPhiIterator phi(block->phisBegin()); phi != block->phisEnd(); ++phi) {
MOZ_ASSERT(!phi->isInWorklist());
bool canProduceFloat32 = true;
for (size_t i = 0, e = phi->numOperands(); canProduceFloat32 && i < e;
++i) {
MDefinition* input = phi->getOperand(i);
canProduceFloat32 &= input->isPhi() || input->canProduceFloat32();
}
phi->setCanProduceFloat32(canProduceFloat32);
if (canProduceFloat32 && !addPhiToWorklist(*phi)) {
return false;
}
}
}
while (!phiWorklist_.empty()) {
if (mir->shouldCancel(
"Ensure Float32 commutativity - Producer Phis - Fixed point")) {
return false;
}
MPhi* phi = popPhi();
MOZ_ASSERT(phi->canProduceFloat32());
bool validProducer = true;
for (size_t i = 0, e = phi->numOperands(); i < e; ++i) {
MDefinition* input = phi->getOperand(i);
if (input->isPhi() && !input->canProduceFloat32()) {
validProducer = false;
break;
}
}
if (validProducer) {
continue;
}
// Propagate invalidated phis
phi->setCanProduceFloat32(false);
for (MUseDefIterator use(phi); use; use++) {
MDefinition* def = use.def();
if (def->isPhi() && !def->isInWorklist() && def->canProduceFloat32()) {
if (!addPhiToWorklist(def->toPhi())) {
return false;
}
}
}
}
return true;
}
bool TypeAnalyzer::specializeValidFloatOps() {
for (ReversePostorderIterator block(graph.rpoBegin());
block != graph.rpoEnd(); ++block) {
if (mir->shouldCancel("Ensure Float32 commutativity - Instructions")) {
return false;
}
for (MInstructionIterator ins(block->begin()); ins != block->end(); ++ins) {
if (!ins->isFloat32Commutative()) {
continue;
}
if (ins->type() == MIRType::Float32) {
continue;
}
if (!alloc().ensureBallast()) {
return false;
}
// This call will try to specialize the instruction iff all uses are
// consumers and all inputs are producers.
ins->trySpecializeFloat32(alloc());
}
}
return true;
}
bool TypeAnalyzer::graphContainsFloat32() {
for (ReversePostorderIterator block(graph.rpoBegin());
block != graph.rpoEnd(); ++block) {
for (MDefinitionIterator def(*block); def; def++) {
if (mir->shouldCancel(
"Ensure Float32 commutativity - Graph contains Float32")) {
return false;
}
if (def->type() == MIRType::Float32) {
return true;
}
}
}
return false;
}
bool TypeAnalyzer::tryEmitFloatOperations() {
// Asm.js uses the ahead of time type checks to specialize operations, no need
// to check them again at this point.
if (mir->compilingWasm()) {
return true;
}
// Check ahead of time that there is at least one definition typed as Float32,
// otherwise we don't need this pass.
if (!graphContainsFloat32()) {
return true;
}
// WarpBuilder skips over code that can't be reached except through
// a catch block. Locals and arguments may be observable in such
// code after bailing out, so we can't rely on seeing all uses.
if (graph.hasTryBlock()) {
return true;
}
if (!markPhiConsumers()) {
return false;
}
if (!markPhiProducers()) {
return false;
}
if (!specializeValidFloatOps()) {
return false;
}
return true;
}
bool TypeAnalyzer::checkFloatCoherency() {
#ifdef DEBUG
// Asserts that all Float32 instructions are flowing into Float32 consumers or
// specialized operations
for (ReversePostorderIterator block(graph.rpoBegin());
block != graph.rpoEnd(); ++block) {
if (mir->shouldCancel("Check Float32 coherency")) {
return false;
}
for (MDefinitionIterator def(*block); def; def++) {
if (def->type() != MIRType::Float32) {
continue;
}
for (MUseDefIterator use(*def); use; use++) {
MDefinition* consumer = use.def();
MOZ_ASSERT(consumer->isConsistentFloat32Use(use.use()));
}
}
}
#endif
return true;
}
static bool HappensBefore(const MDefinition* earlier,
const MDefinition* later) {
MOZ_ASSERT(earlier->block() == later->block());
for (auto* ins : *earlier->block()) {
if (ins == earlier) {
return true;
}
if (ins == later) {
return false;
}
}
MOZ_CRASH("earlier and later are instructions in the block");
}
// Propagate type information from dominating unbox instructions.
//
// This optimization applies for example for self-hosted String.prototype
// functions.
//
// Example:
// ```
// String.prototype.id = function() {
// // Strict mode to avoid ToObject on primitive this-values.
// "use strict";
//
// // Template string to apply ToString on the this-value.
// return `${this}`;
// };
//
// function f(s) {
// // Assume |s| is a string value.
// return s.id();
// }
// ```
//
// Compiles into: (Graph after Scalar Replacement)
//
// ┌───────────────────────────────────────────────────────────────────────────┐
// │ Block 0 │
// │ resumepoint 1 0 2 2 │
// │ 0 parameter THIS_SLOT Value │
// │ 1 parameter 0 Value │
// │ 2 constant undefined Undefined │
// │ 3 start │
// │ 4 checkoverrecursed │
// │ 5 unbox parameter1 to String (fallible) String │
// │ 6 constant object 1d908053e088 (String) Object │
// │ 7 guardshape constant6:Object Object │
// │ 8 slots guardshape7:Object Slots │
// │ 9 loaddynamicslot slots8:Slots (slot 53) Value │
// │ 10 constant 0x0 Int32 │
// │ 11 unbox loaddynamicslot9 to Object (fallible) Object │
// │ 12 nurseryobject Object │
// │ 13 guardspecificfunction unbox11:Object nurseryobject12:Object Object │
// │ 14 goto block1 │
// └──────────────────────────────────┬────────────────────────────────────────┘
// │
// ┌──────────────────────────────────▼────────────────────────────────────────┐
// │ Block 1 │
// │ ((0)) resumepoint 15 1 15 15 | 1 13 1 0 2 2 │
// │ 15 constant undefined Undefined │
// │ 16 tostring parameter1:Value String │
// │ 18 goto block2 │
// └──────────────────────────────────┬────────────────────────────────────────┘
// │
// ┌──────────────▼──────────────┐
// │ Block 2 │
// │ resumepoint 16 1 0 2 2 │
// │ 19 return tostring16:String │
// └─────────────────────────────┘
//
// The Unbox instruction is used as a type guard. The ToString instruction
// doesn't use the type information from the preceding Unbox instruction and
// therefore has to assume its operand can be any value.
//
// When instead propagating the type information from the preceding Unbox
// instruction, this graph is constructed after the "Apply types" phase:
//
// ┌───────────────────────────────────────────────────────────────────────────┐
// │ Block 0 │
// │ resumepoint 1 0 2 2 │
// │ 0 parameter THIS_SLOT Value │
// │ 1 parameter 0 Value │
// │ 2 constant undefined Undefined │
// │ 3 start │
// │ 4 checkoverrecursed │
// │ 5 unbox parameter1 to String (fallible) String │
// │ 6 constant object 1d908053e088 (String) Object │
// │ 7 guardshape constant6:Object Object │
// │ 8 slots guardshape7:Object Slots │
// │ 9 loaddynamicslot slots8:Slots (slot 53) Value │
// │ 10 constant 0x0 Int32 │
// │ 11 unbox loaddynamicslot9 to Object (fallible) Object │
// │ 12 nurseryobject Object │
// │ 13 guardspecificfunction unbox11:Object nurseryobject12:Object Object │
// │ 14 goto block1 │
// └──────────────────────────────────┬────────────────────────────────────────┘
// │
// ┌──────────────────────────────────▼────────────────────────────────────────┐
// │ Block 1 │
// │ ((0)) resumepoint 15 1 15 15 | 1 13 1 0 2 2 │
// │ 15 constant undefined Undefined │
// │ 20 unbox parameter1 to String (fallible) String │
// │ 16 tostring parameter1:Value String │
// │ 18 goto block2 │
// └──────────────────────────────────┬────────────────────────────────────────┘
// │
// ┌──────────────▼─────────────────────┐
// │ Block 2 │
// │ resumepoint 16 1 0 2 2 │
// │ 21 box tostring16:String Value │
// │ 19 return box21:Value │
// └────────────────────────────────────┘
//
// GVN will later merge both Unbox instructions and fold away the ToString
// instruction, so we get this final graph:
//
// ┌───────────────────────────────────────────────────────────────────────────┐
// │ Block 0 │
// │ resumepoint 1 0 2 2 │
// │ 0 parameter THIS_SLOT Value │
// │ 1 parameter 0 Value │
// │ 2 constant undefined Undefined │
// │ 3 start │
// │ 4 checkoverrecursed │
// │ 5 unbox parameter1 to String (fallible) String │
// │ 6 constant object 1d908053e088 (String) Object │
// │ 7 guardshape constant6:Object Object │
// │ 8 slots guardshape7:Object Slots │
// │ 22 loaddynamicslotandunbox slots8:Slots (slot 53) Object │
// │ 11 nurseryobject Object │
// │ 12 guardspecificfunction load22:Object nurseryobject11:Object Object │
// │ 13 goto block1 │
// └──────────────────────────────────┬────────────────────────────────────────┘
// │
// ┌──────────────────────────────────▼────────────────────────────────────────┐
// │ Block 1 │
// │ ((0)) resumepoint 2 1 2 2 | 1 12 1 0 2 2 │
// │ 14 goto block2 │
// └──────────────────────────────────┬────────────────────────────────────────┘
// │
// ┌──────────────▼─────────────────────┐
// │ Block 2 │
// │ resumepoint 5 1 0 2 2 │
// │ 15 return parameter1:Value │
// └────────────────────────────────────┘
//
bool TypeAnalyzer::propagateUnbox() {
// Visit the blocks in post-order, so that the type information of the closest
// unbox operation is used.
for (PostorderIterator block(graph.poBegin()); block != graph.poEnd();
block++) {
if (mir->shouldCancel("Propagate Unbox")) {
return false;
}
// Iterate over all instructions to look for unbox instructions.
for (MInstructionIterator iter(block->begin()); iter != block->end();
iter++) {
if (!iter->isUnbox()) {
continue;
}
auto* unbox = iter->toUnbox();
auto* input = unbox->input();
// Ignore unbox operations on typed values.
if (input->type() != MIRType::Value) {
continue;
}
// Ignore unbox to floating point types, because propagating boxed Int32
// values as Double can lead to repeated bailouts when later instructions
// expect Int32 inputs.
if (IsFloatingPointType(unbox->type())) {
continue;
}
// Inspect other uses of |input| to propagate the unboxed type information
// from |unbox|.
for (auto uses = input->usesBegin(); uses != input->usesEnd();) {
auto* use = *uses++;
// Ignore resume points.
if (!use->consumer()->isDefinition()) {
continue;
}
auto* def = use->consumer()->toDefinition();
// Ignore any unbox operations, including the current |unbox|.
if (def->isUnbox()) {
continue;
}
// Ignore phi nodes, because we don't yet support them.
if (def->isPhi()) {
continue;
}
// The unbox operation needs to happen before the other use, otherwise
// we can't propagate the type information.
if (unbox->block() == def->block()) {
if (!HappensBefore(unbox, def)) {
continue;
}
} else {
if (!unbox->block()->dominates(def->block())) {
continue;
}
}
// Replace the use with |unbox|, so that GVN knows about the actual
// value type and can more easily fold unnecessary operations. If the
// instruction actually needs a boxed input, the BoxPolicy type policy
// will simply unwrap the unbox instruction.
use->replaceProducer(unbox);
// The uses in the MIR graph no longer reflect the uses in the bytecode,
// so we have to mark |input| as implicitly used.
input->setImplicitlyUsedUnchecked();
}
}
}
return true;
}
bool TypeAnalyzer::analyze() {
if (!tryEmitFloatOperations()) {
return false;
}
if (!specializePhis()) {
return false;
}
if (!propagateUnbox()) {
return false;
}
if (!insertConversions()) {
return false;
}
if (!checkFloatCoherency()) {
return false;
}
return true;
}
bool jit::ApplyTypeInformation(const MIRGenerator* mir, MIRGraph& graph) {
TypeAnalyzer analyzer(mir, graph);
if (!analyzer.analyze()) {
return false;
}
return true;
}
void jit::RenumberBlocks(MIRGraph& graph) {
size_t id = 0;
for (ReversePostorderIterator block(graph.rpoBegin());
block != graph.rpoEnd(); block++) {
block->setId(id++);
}
}
// A utility for code which adds/deletes blocks. Renumber the remaining blocks,
// recompute dominators, and optionally recompute AliasAnalysis dependencies.
bool jit::AccountForCFGChanges(const MIRGenerator* mir, MIRGraph& graph,
bool updateAliasAnalysis,
bool underValueNumberer) {
// Renumber the blocks and clear out the old dominator info.
size_t id = 0;
for (ReversePostorderIterator i(graph.rpoBegin()), e(graph.rpoEnd()); i != e;
++i) {
i->clearDominatorInfo();
i->setId(id++);
}
// Recompute dominator info.
if (!BuildDominatorTree(mir, graph)) {
return false;
}
// If needed, update alias analysis dependencies.
if (updateAliasAnalysis) {
if (!AliasAnalysis(mir, graph).analyze()) {
return false;
}
}
AssertExtendedGraphCoherency(graph, underValueNumberer);
return true;
}
// Remove all blocks not marked with isMarked(). Unmark all remaining blocks.
// Alias analysis dependencies may be invalid after calling this function.
bool jit::RemoveUnmarkedBlocks(const MIRGenerator* mir, MIRGraph& graph,
uint32_t numMarkedBlocks) {
if (numMarkedBlocks == graph.numBlocks()) {
// If all blocks are marked, no blocks need removal. Just clear the
// marks. We'll still need to update the dominator tree below though,
// since we may have removed edges even if we didn't remove any blocks.
graph.unmarkBlocks();
} else {
// As we are going to remove edges and basic blocks, we have to mark
// instructions which would be needed by baseline if we were to
// bailout.
for (PostorderIterator it(graph.poBegin()); it != graph.poEnd();) {
MBasicBlock* block = *it++;
if (block->isMarked()) {
continue;
}
if (!FlagAllOperandsAsImplicitlyUsed(mir, block)) {
return false;
}
}
// Find unmarked blocks and remove them.
for (ReversePostorderIterator iter(graph.rpoBegin());
iter != graph.rpoEnd();) {
MBasicBlock* block = *iter++;
if (block->isMarked()) {
block->unmark();
continue;
}
// The block is unreachable. Clear out the loop header flag, as
// we're doing the sweep of a mark-and-sweep here, so we no longer
// need to worry about whether an unmarked block is a loop or not.
if (block->isLoopHeader()) {
block->clearLoopHeader();
}
for (size_t i = 0, e = block->numSuccessors(); i != e; ++i) {
block->getSuccessor(i)->removePredecessor(block);
}
graph.removeBlock(block);
}
}
// Renumber the blocks and update the dominator tree.
return AccountForCFGChanges(mir, graph, /*updateAliasAnalysis=*/false);
}
bool jit::BuildPhiReverseMapping(MIRGraph& graph) {
// Build a mapping such that given a basic block, whose successor has one or
// more phis, we can find our specific input to that phi. To make this fast
// mapping work we rely on a specific property of our structured control
// flow graph: For a block with phis, its predecessors each have only one
// successor with phis. Consider each case:
// * Blocks with less than two predecessors cannot have phis.
// * Breaks. A break always has exactly one successor, and the break
// catch block has exactly one predecessor for each break, as
// well as a final predecessor for the actual loop exit.
// * Continues. A continue always has exactly one successor, and the
// continue catch block has exactly one predecessor for each
// continue, as well as a final predecessor for the actual
// loop continuation. The continue itself has exactly one
// successor.
// * An if. Each branch as exactly one predecessor.
// * A switch. Each branch has exactly one predecessor.
// * Loop tail. A new block is always created for the exit, and if a
// break statement is present, the exit block will forward
// directly to the break block.
for (MBasicBlockIterator block(graph.begin()); block != graph.end();
block++) {
if (block->phisEmpty()) {
continue;
}
// Assert on the above.
for (size_t j = 0; j < block->numPredecessors(); j++) {
MBasicBlock* pred = block->getPredecessor(j);
#ifdef DEBUG
size_t numSuccessorsWithPhis = 0;
for (size_t k = 0; k < pred->numSuccessors(); k++) {
MBasicBlock* successor = pred->getSuccessor(k);
if (!successor->phisEmpty()) {
numSuccessorsWithPhis++;
}
}
MOZ_ASSERT(numSuccessorsWithPhis <= 1);
#endif
pred->setSuccessorWithPhis(*block, j);
}
}
return true;
}
#ifdef DEBUG
static bool CheckSuccessorImpliesPredecessor(MBasicBlock* A, MBasicBlock* B) {
// Assuming B = succ(A), verify A = pred(B).
for (size_t i = 0; i < B->numPredecessors(); i++) {
if (A == B->getPredecessor(i)) {
return true;
}
}
return false;
}
static bool CheckPredecessorImpliesSuccessor(MBasicBlock* A, MBasicBlock* B) {
// Assuming B = pred(A), verify A = succ(B).
for (size_t i = 0; i < B->numSuccessors(); i++) {
if (A == B->getSuccessor(i)) {
return true;
}
}
return false;
}
// If you have issues with the usesBalance assertions, then define the macro
// _DEBUG_CHECK_OPERANDS_USES_BALANCE to spew information on the error output.
// This output can then be processed with the following awk script to filter and
// highlight which checks are missing or if there is an unexpected operand /
// use.
//
// define _DEBUG_CHECK_OPERANDS_USES_BALANCE 1
/*
$ ./js 2>stderr.log
$ gawk '
/^==Check/ { context = ""; state = $2; }
/^[a-z]/ { context = context "\n\t" $0; }
/^==End/ {
if (state == "Operand") {
list[context] = list[context] - 1;
} else if (state == "Use") {
list[context] = list[context] + 1;
}
}
END {
for (ctx in list) {
if (list[ctx] > 0) {
print "Missing operand check", ctx, "\n"
}
if (list[ctx] < 0) {
print "Missing use check", ctx, "\n"
}
};
}' < stderr.log
*/
static void CheckOperand(const MNode* consumer, const MUse* use,
int32_t* usesBalance) {
MOZ_ASSERT(use->hasProducer());
MDefinition* producer = use->producer();
MOZ_ASSERT(!producer->isDiscarded());
MOZ_ASSERT(producer->block() != nullptr);
MOZ_ASSERT(use->consumer() == consumer);
# ifdef _DEBUG_CHECK_OPERANDS_USES_BALANCE
Fprinter print(stderr);
print.printf("==Check Operand\n");
use->producer()->dump(print);
print.printf(" index: %zu\n", use->consumer()->indexOf(use));
use->consumer()->dump(print);
print.printf("==End\n");
# endif
--*usesBalance;
}
static void CheckUse(const MDefinition* producer, const MUse* use,
int32_t* usesBalance) {
MOZ_ASSERT(!use->consumer()->block()->isDead());
MOZ_ASSERT_IF(use->consumer()->isDefinition(),
!use->consumer()->toDefinition()->isDiscarded());
MOZ_ASSERT(use->consumer()->block() != nullptr);
MOZ_ASSERT(use->consumer()->getOperand(use->index()) == producer);
# ifdef _DEBUG_CHECK_OPERANDS_USES_BALANCE
Fprinter print(stderr);
print.printf("==Check Use\n");
use->producer()->dump(print);
print.printf(" index: %zu\n", use->consumer()->indexOf(use));
use->consumer()->dump(print);
print.printf("==End\n");
# endif
++*usesBalance;
}
// To properly encode entry resume points, we have to ensure that all the
// operands of the entry resume point are located before the safeInsertTop
// location.
static void AssertOperandsBeforeSafeInsertTop(MResumePoint* resume) {
MBasicBlock* block = resume->block();
if (block == block->graph().osrBlock()) {
return;
}
MInstruction* stop = block->safeInsertTop();
for (size_t i = 0, e = resume->numOperands(); i < e; ++i) {
MDefinition* def = resume->getOperand(i);
if (def->block() != block) {
continue;
}
if (def->isPhi()) {
continue;
}
for (MInstructionIterator ins = block->begin(); true; ins++) {
if (*ins == def) {
break;
}
MOZ_ASSERT(
*ins != stop,
"Resume point operand located after the safeInsertTop location");
}
}
}
#endif // DEBUG
void jit::AssertBasicGraphCoherency(MIRGraph& graph, bool force) {
#ifdef DEBUG
if (!JitOptions.fullDebugChecks && !force) {
return;
}
MOZ_ASSERT(graph.entryBlock()->numPredecessors() == 0);
MOZ_ASSERT(graph.entryBlock()->phisEmpty());
MOZ_ASSERT(!graph.entryBlock()->unreachable());
if (MBasicBlock* osrBlock = graph.osrBlock()) {
MOZ_ASSERT(osrBlock->numPredecessors() == 0);
MOZ_ASSERT(osrBlock->phisEmpty());
MOZ_ASSERT(osrBlock != graph.entryBlock());
MOZ_ASSERT(!osrBlock->unreachable());
}
if (MResumePoint* resumePoint = graph.entryResumePoint()) {
MOZ_ASSERT(resumePoint->block() == graph.entryBlock());
}
// Assert successor and predecessor list coherency.
uint32_t count = 0;
int32_t usesBalance = 0;
for (MBasicBlockIterator block(graph.begin()); block != graph.end();
block++) {
count++;
MOZ_ASSERT(&block->graph() == &graph);
MOZ_ASSERT(!block->isDead());
MOZ_ASSERT_IF(block->outerResumePoint() != nullptr,
block->entryResumePoint() != nullptr);
for (size_t i = 0; i < block->numSuccessors(); i++) {
MOZ_ASSERT(
CheckSuccessorImpliesPredecessor(*block, block->getSuccessor(i)));
}
for (size_t i = 0; i < block->numPredecessors(); i++) {
MOZ_ASSERT(
CheckPredecessorImpliesSuccessor(*block, block->getPredecessor(i)));
}
if (MResumePoint* resume = block->entryResumePoint()) {
MOZ_ASSERT(!resume->instruction());
MOZ_ASSERT(resume->block() == *block);
AssertOperandsBeforeSafeInsertTop(resume);
}
if (MResumePoint* resume = block->outerResumePoint()) {
MOZ_ASSERT(!resume->instruction());
MOZ_ASSERT(resume->block() == *block);
}
for (MResumePointIterator iter(block->resumePointsBegin());
iter != block->resumePointsEnd(); iter++) {
// We cannot yet assert that is there is no instruction then this is
// the entry resume point because we are still storing resume points
// in the InlinePropertyTable.
MOZ_ASSERT_IF(iter->instruction(),
iter->instruction()->block() == *block);
for (uint32_t i = 0, e = iter->numOperands(); i < e; i++) {
CheckOperand(*iter, iter->getUseFor(i), &usesBalance);
}
}
for (MPhiIterator phi(block->phisBegin()); phi != block->phisEnd(); phi++) {
MOZ_ASSERT(phi->numOperands() == block->numPredecessors());
MOZ_ASSERT(!phi->isRecoveredOnBailout());
MOZ_ASSERT(phi->type() != MIRType::None);
MOZ_ASSERT(phi->dependency() == nullptr);
}
for (MDefinitionIterator iter(*block); iter; iter++) {
MOZ_ASSERT(iter->block() == *block);
MOZ_ASSERT_IF(iter->hasUses(), iter->type() != MIRType::None);
MOZ_ASSERT(!iter->isDiscarded());
MOZ_ASSERT_IF(iter->isStart(),
*block == graph.entryBlock() || *block == graph.osrBlock());
MOZ_ASSERT_IF(iter->isParameter(),
*block == graph.entryBlock() || *block == graph.osrBlock());
MOZ_ASSERT_IF(iter->isOsrEntry(), *block == graph.osrBlock());
MOZ_ASSERT_IF(iter->isOsrValue(), *block == graph.osrBlock());
// Assert that use chains are valid for this instruction.
for (uint32_t i = 0, end = iter->numOperands(); i < end; i++) {
CheckOperand(*iter, iter->getUseFor(i), &usesBalance);
}
for (MUseIterator use(iter->usesBegin()); use != iter->usesEnd(); use++) {
CheckUse(*iter, *use, &usesBalance);
}
if (iter->isInstruction()) {
if (MResumePoint* resume = iter->toInstruction()->resumePoint()) {
MOZ_ASSERT(resume->instruction() == *iter);
MOZ_ASSERT(resume->block() == *block);
MOZ_ASSERT(resume->block()->entryResumePoint() != nullptr);
}
}
if (iter->isRecoveredOnBailout()) {
MOZ_ASSERT(!iter->hasLiveDefUses());
}
}
// The control instruction is not visited by the MDefinitionIterator.
MControlInstruction* control = block->lastIns();
MOZ_ASSERT(control->block() == *block);
MOZ_ASSERT(!control->hasUses());
MOZ_ASSERT(control->type() == MIRType::None);
MOZ_ASSERT(!control->isDiscarded());
MOZ_ASSERT(!control->isRecoveredOnBailout());
MOZ_ASSERT(control->resumePoint() == nullptr);
for (uint32_t i = 0, end = control->numOperands(); i < end; i++) {
CheckOperand(control, control->getUseFor(i), &usesBalance);
}
for (size_t i = 0; i < control->numSuccessors(); i++) {
MOZ_ASSERT(control->getSuccessor(i));
}
}
// In case issues, see the _DEBUG_CHECK_OPERANDS_USES_BALANCE macro above.
MOZ_ASSERT(usesBalance <= 0, "More use checks than operand checks");
MOZ_ASSERT(usesBalance >= 0, "More operand checks than use checks");
MOZ_ASSERT(graph.numBlocks() == count);
#endif
}
#ifdef DEBUG
static void AssertReversePostorder(MIRGraph& graph) {
// Check that every block is visited after all its predecessors (except
// backedges).
for (ReversePostorderIterator iter(graph.rpoBegin()); iter != graph.rpoEnd();
++iter) {
MBasicBlock* block = *iter;
MOZ_ASSERT(!block->isMarked());
for (size_t i = 0; i < block->numPredecessors(); i++) {
MBasicBlock* pred = block->getPredecessor(i);
if (!pred->isMarked()) {
MOZ_ASSERT(pred->isLoopBackedge());
MOZ_ASSERT(block->backedge() == pred);
}
}
block->mark();
}
graph.unmarkBlocks();
}
#endif
#ifdef DEBUG
static void AssertDominatorTree(MIRGraph& graph) {
// Check dominators.
MOZ_ASSERT(graph.entryBlock()->immediateDominator() == graph.entryBlock());
if (MBasicBlock* osrBlock = graph.osrBlock()) {
MOZ_ASSERT(osrBlock->immediateDominator() == osrBlock);
} else {
MOZ_ASSERT(graph.entryBlock()->numDominated() == graph.numBlocks());
}
size_t i = graph.numBlocks();
size_t totalNumDominated = 0;
for (MBasicBlockIterator block(graph.begin()); block != graph.end();
block++) {
MOZ_ASSERT(block->dominates(*block));
MBasicBlock* idom = block->immediateDominator();
MOZ_ASSERT(idom->dominates(*block));
MOZ_ASSERT(idom == *block || idom->id() < block->id());
if (idom == *block) {
totalNumDominated += block->numDominated();
} else {
bool foundInParent = false;
for (size_t j = 0; j < idom->numImmediatelyDominatedBlocks(); j++) {
if (idom->getImmediatelyDominatedBlock(j) == *block) {
foundInParent = true;
break;
}
}
MOZ_ASSERT(foundInParent);
}
size_t numDominated = 1;
for (size_t j = 0; j < block->numImmediatelyDominatedBlocks(); j++) {
MBasicBlock* dom = block->getImmediatelyDominatedBlock(j);
MOZ_ASSERT(block->dominates(dom));
MOZ_ASSERT(dom->id() > block->id());
MOZ_ASSERT(dom->immediateDominator() == *block);
numDominated += dom->numDominated();
}
MOZ_ASSERT(block->numDominated() == numDominated);
MOZ_ASSERT(block->numDominated() <= i);
MOZ_ASSERT(block->numSuccessors() != 0 || block->numDominated() == 1);
i--;
}
MOZ_ASSERT(i == 0);
MOZ_ASSERT(totalNumDominated == graph.numBlocks());
}
#endif
void jit::AssertGraphCoherency(MIRGraph& graph, bool force) {
#ifdef DEBUG
if (!JitOptions.checkGraphConsistency) {
return;
}
if (!JitOptions.fullDebugChecks && !force) {
return;
}
AssertBasicGraphCoherency(graph, force);
AssertReversePostorder(graph);
#endif
}
#ifdef DEBUG
static bool IsResumableMIRType(MIRType type) {
// see CodeGeneratorShared::encodeAllocation
switch (type) {
case MIRType::Undefined:
case MIRType::Null:
case MIRType::Boolean:
case MIRType::Int32:
case MIRType::Double:
case MIRType::Float32:
case MIRType::String:
case MIRType::Symbol:
case MIRType::BigInt:
case MIRType::Object:
case MIRType::Shape:
case MIRType::MagicOptimizedOut:
case MIRType::MagicUninitializedLexical:
case MIRType::MagicIsConstructing:
case MIRType::Value:
case MIRType::Int64:
case MIRType::IntPtr:
return true;
case MIRType::Simd128:
case MIRType::MagicHole:
case MIRType::None:
case MIRType::Slots:
case MIRType::Elements:
case MIRType::Pointer:
case MIRType::WasmAnyRef:
case MIRType::WasmArrayData:
case MIRType::StackResults:
return false;
}
MOZ_CRASH("Unknown MIRType.");
}
static void AssertResumableOperands(MNode* node) {
for (size_t i = 0, e = node->numOperands(); i < e; ++i) {
MDefinition* op = node->getOperand(i);
if (op->isRecoveredOnBailout()) {
continue;
}
MOZ_ASSERT(IsResumableMIRType(op->type()),
"Resume point cannot encode its operands");
}
}
static void AssertIfResumableInstruction(MDefinition* def) {
if (!def->isRecoveredOnBailout()) {
return;
}
AssertResumableOperands(def);
}
static void AssertResumePointDominatedByOperands(MResumePoint* resume) {
for (size_t i = 0, e = resume->numOperands(); i < e; ++i) {
MDefinition* op = resume->getOperand(i);
MOZ_ASSERT(op->block()->dominates(resume->block()),
"Resume point is not dominated by its operands");
}
}
#endif // DEBUG
// Checks the basic GraphCoherency but also other conditions that
// do not hold immediately (such as the fact that critical edges
// are split, or conditions related to wasm semantics)
void jit::AssertExtendedGraphCoherency(MIRGraph& graph, bool underValueNumberer,
bool force) {
#ifdef DEBUG
if (!JitOptions.checkGraphConsistency) {
return;
}
if (!JitOptions.fullDebugChecks && !force) {
return;
}
AssertGraphCoherency(graph, force);
AssertDominatorTree(graph);
DebugOnly<uint32_t> idx = 0;
for (MBasicBlockIterator block(graph.begin()); block != graph.end();
block++) {
MOZ_ASSERT(block->id() == idx);
++idx;
// No critical edges:
if (block->numSuccessors() > 1) {
for (size_t i = 0; i < block->numSuccessors(); i++) {
MOZ_ASSERT(block->getSuccessor(i)->numPredecessors() == 1);
}
}
if (block->isLoopHeader()) {
if (underValueNumberer && block->numPredecessors() == 3) {
// Fixup block.
MOZ_ASSERT(block->getPredecessor(1)->numPredecessors() == 0);
MOZ_ASSERT(graph.osrBlock(),
"Fixup blocks should only exists if we have an osr block.");
} else {
MOZ_ASSERT(block->numPredecessors() == 2);
}
MBasicBlock* backedge = block->backedge();
MOZ_ASSERT(backedge->id() >= block->id());
MOZ_ASSERT(backedge->numSuccessors() == 1);
MOZ_ASSERT(backedge->getSuccessor(0) == *block);
}
if (!block->phisEmpty()) {
for (size_t i = 0; i < block->numPredecessors(); i++) {
MBasicBlock* pred = block->getPredecessor(i);
MOZ_ASSERT(pred->successorWithPhis() == *block);
MOZ_ASSERT(pred->positionInPhiSuccessor() == i);
}
}
uint32_t successorWithPhis = 0;
for (size_t i = 0; i < block->numSuccessors(); i++) {
if (!block->getSuccessor(i)->phisEmpty()) {
successorWithPhis++;
}
}
MOZ_ASSERT(successorWithPhis <= 1);
MOZ_ASSERT((successorWithPhis != 0) ==
(block->successorWithPhis() != nullptr));
// Verify that phi operands dominate the corresponding CFG predecessor
// edges.
for (MPhiIterator iter(block->phisBegin()), end(block->phisEnd());
iter != end; ++iter) {
MPhi* phi = *iter;
for (size_t i = 0, e = phi->numOperands(); i < e; ++i) {
MOZ_ASSERT(
phi->getOperand(i)->block()->dominates(block->getPredecessor(i)),
"Phi input is not dominated by its operand");
}
}
// Verify that instructions are dominated by their operands.
for (MInstructionIterator iter(block->begin()), end(block->end());
iter != end; ++iter) {
MInstruction* ins = *iter;
for (size_t i = 0, e = ins->numOperands(); i < e; ++i) {
MDefinition* op = ins->getOperand(i);
MBasicBlock* opBlock = op->block();
MOZ_ASSERT(opBlock->dominates(*block),
"Instruction is not dominated by its operands");
// If the operand is an instruction in the same block, check
// that it comes first.
if (opBlock == *block && !op->isPhi()) {
MInstructionIterator opIter = block->begin(op->toInstruction());
do {
++opIter;
MOZ_ASSERT(opIter != block->end(),
"Operand in same block as instruction does not precede");
} while (*opIter != ins);
}
}
AssertIfResumableInstruction(ins);
if (MResumePoint* resume = ins->resumePoint()) {
AssertResumePointDominatedByOperands(resume);
AssertResumableOperands(resume);
}
}
// Verify that the block resume points are dominated by their operands.
if (MResumePoint* resume = block->entryResumePoint()) {
AssertResumePointDominatedByOperands(resume);
AssertResumableOperands(resume);
}
if (MResumePoint* resume = block->outerResumePoint()) {
AssertResumePointDominatedByOperands(resume);
AssertResumableOperands(resume);
}
// Verify that any nodes with a wasm ref type have MIRType WasmAnyRef.
for (MDefinitionIterator def(*block); def; def++) {
MOZ_ASSERT_IF(def->wasmRefType().isSome(),
def->type() == MIRType::WasmAnyRef);
}
}
#endif
}
struct BoundsCheckInfo {
MBoundsCheck* check;
uint32_t validEnd;
};
using BoundsCheckMap =
HashMap<uint32_t, BoundsCheckInfo, DefaultHasher<uint32_t>, JitAllocPolicy>;
// Compute a hash for bounds checks which ignores constant offsets in the index.
static HashNumber BoundsCheckHashIgnoreOffset(MBoundsCheck* check) {
SimpleLinearSum indexSum = ExtractLinearSum(check->index());
uintptr_t index = indexSum.term ? uintptr_t(indexSum.term) : 0;
uintptr_t length = uintptr_t(check->length());
return index ^ length;
}
static MBoundsCheck* FindDominatingBoundsCheck(BoundsCheckMap& checks,
MBoundsCheck* check,
size_t index) {
// Since we are traversing the dominator tree in pre-order, when we
// are looking at the |index|-th block, the next numDominated() blocks
// we traverse are precisely the set of blocks that are dominated.
//
// So, this value is visible in all blocks if:
// index <= index + ins->block->numDominated()
// and becomes invalid after that.
HashNumber hash = BoundsCheckHashIgnoreOffset(check);
BoundsCheckMap::Ptr p = checks.lookup(hash);
if (!p || index >= p->value().validEnd) {
// We didn't find a dominating bounds check.
BoundsCheckInfo info;
info.check = check;
info.validEnd = index + check->block()->numDominated();
if (!checks.put(hash, info)) return nullptr;
return check;
}
return p->value().check;
}
static MathSpace ExtractMathSpace(MDefinition* ins) {
MOZ_ASSERT(ins->isAdd() || ins->isSub());
MBinaryArithInstruction* arith = nullptr;
if (ins->isAdd()) {
arith = ins->toAdd();
} else {
arith = ins->toSub();
}
switch (arith->truncateKind()) {
case TruncateKind::NoTruncate:
case TruncateKind::TruncateAfterBailouts:
// TruncateAfterBailouts is considered as infinite space because the
// LinearSum will effectively remove the bailout check.
return MathSpace::Infinite;
case TruncateKind::IndirectTruncate:
case TruncateKind::Truncate:
return MathSpace::Modulo;
}
MOZ_CRASH("Unknown TruncateKind");
}
static bool MonotoneAdd(int32_t lhs, int32_t rhs) {
return (lhs >= 0 && rhs >= 0) || (lhs <= 0 && rhs <= 0);
}
static bool MonotoneSub(int32_t lhs, int32_t rhs) {
return (lhs >= 0 && rhs <= 0) || (lhs <= 0 && rhs >= 0);
}
// Extract a linear sum from ins, if possible (otherwise giving the
// sum 'ins + 0').
SimpleLinearSum jit::ExtractLinearSum(MDefinition* ins, MathSpace space,
int32_t recursionDepth) {
const int32_t SAFE_RECURSION_LIMIT = 100;
if (recursionDepth > SAFE_RECURSION_LIMIT) {
return SimpleLinearSum(ins, 0);
}
// Unwrap Int32ToIntPtr. This instruction only changes the representation
// (int32_t to intptr_t) without affecting the value.
if (ins->isInt32ToIntPtr()) {
ins = ins->toInt32ToIntPtr()->input();
}
if (ins->isBeta()) {
ins = ins->getOperand(0);
}
MOZ_ASSERT(!ins->isInt32ToIntPtr());
if (ins->type() != MIRType::Int32) {
return SimpleLinearSum(ins, 0);
}
if (ins->isConstant()) {
return SimpleLinearSum(nullptr, ins->toConstant()->toInt32());
}
if (!ins->isAdd() && !ins->isSub()) {
return SimpleLinearSum(ins, 0);
}
// Only allow math which are in the same space.
MathSpace insSpace = ExtractMathSpace(ins);
if (space == MathSpace::Unknown) {
space = insSpace;
} else if (space != insSpace) {
return SimpleLinearSum(ins, 0);
}
MOZ_ASSERT(space == MathSpace::Modulo || space == MathSpace::Infinite);
MDefinition* lhs = ins->getOperand(0);
MDefinition* rhs = ins->getOperand(1);
if (lhs->type() != MIRType::Int32 || rhs->type() != MIRType::Int32) {
return SimpleLinearSum(ins, 0);
}
// Extract linear sums of each operand.
SimpleLinearSum lsum = ExtractLinearSum(lhs, space, recursionDepth + 1);
SimpleLinearSum rsum = ExtractLinearSum(rhs, space, recursionDepth + 1);
// LinearSum only considers a single term operand, if both sides have
// terms, then ignore extracted linear sums.
if (lsum.term && rsum.term) {
return SimpleLinearSum(ins, 0);
}
// Check if this is of the form <SUM> + n or n + <SUM>.
if (ins->isAdd()) {
int32_t constant;
if (space == MathSpace::Modulo) {
constant = uint32_t(lsum.constant) + uint32_t(rsum.constant);
} else if (!SafeAdd(lsum.constant, rsum.constant, &constant) ||
!MonotoneAdd(lsum.constant, rsum.constant)) {
return SimpleLinearSum(ins, 0);
}
return SimpleLinearSum(lsum.term ? lsum.term : rsum.term, constant);
}
MOZ_ASSERT(ins->isSub());
// Check if this is of the form <SUM> - n.
if (lsum.term) {
int32_t constant;
if (space == MathSpace::Modulo) {
constant = uint32_t(lsum.constant) - uint32_t(rsum.constant);
} else if (!SafeSub(lsum.constant, rsum.constant, &constant) ||
!MonotoneSub(lsum.constant, rsum.constant)) {
return SimpleLinearSum(ins, 0);
}
return SimpleLinearSum(lsum.term, constant);
}
// Ignore any of the form n - <SUM>.
return SimpleLinearSum(ins, 0);
}
// Extract a linear inequality holding when a boolean test goes in the
// specified direction, of the form 'lhs + lhsN <= rhs' (or >=).
bool jit::ExtractLinearInequality(const MTest* test, BranchDirection direction,
SimpleLinearSum* plhs, MDefinition** prhs,
bool* plessEqual) {
if (!test->getOperand(0)->isCompare()) {
return false;
}
MCompare* compare = test->getOperand(0)->toCompare();
MDefinition* lhs = compare->getOperand(0);
MDefinition* rhs = compare->getOperand(1);
// TODO: optimize Compare_UInt32
if (!compare->isInt32Comparison()) {
return false;
}
MOZ_ASSERT(lhs->type() == MIRType::Int32);
MOZ_ASSERT(rhs->type() == MIRType::Int32);
JSOp jsop = compare->jsop();
if (direction == FALSE_BRANCH) {
jsop = NegateCompareOp(jsop);
}
SimpleLinearSum lsum = ExtractLinearSum(lhs);
SimpleLinearSum rsum = ExtractLinearSum(rhs);
if (!SafeSub(lsum.constant, rsum.constant, &lsum.constant)) {
return false;
}
// Normalize operations to use <= or >=.
switch (jsop) {
case JSOp::Le:
*plessEqual = true;
break;
case JSOp::Lt:
/* x < y ==> x + 1 <= y */
if (!SafeAdd(lsum.constant, 1, &lsum.constant)) {
return false;
}
*plessEqual = true;
break;
case JSOp::Ge:
*plessEqual = false;
break;
case JSOp::Gt:
/* x > y ==> x - 1 >= y */
if (!SafeSub(lsum.constant, 1, &lsum.constant)) {
return false;
}
*plessEqual = false;
break;
default:
return false;
}
*plhs = lsum;
*prhs = rsum.term;
return true;
}
static bool TryEliminateBoundsCheck(BoundsCheckMap& checks, size_t blockIndex,
MBoundsCheck* dominated, bool* eliminated) {
MOZ_ASSERT(!*eliminated);
// Replace all uses of the bounds check with the actual index.
// This is (a) necessary, because we can coalesce two different
// bounds checks and would otherwise use the wrong index and
// (b) helps register allocation. Note that this is safe since
// no other pass after bounds check elimination moves instructions.
dominated->replaceAllUsesWith(dominated->index());
if (!dominated->isMovable()) {
return true;
}
if (!dominated->fallible()) {
return true;
}
MBoundsCheck* dominating =
FindDominatingBoundsCheck(checks, dominated, blockIndex);
if (!dominating) {
return false;
}
if (dominating == dominated) {
// We didn't find a dominating bounds check.
return true;
}
// We found two bounds checks with the same hash number, but we still have
// to make sure the lengths and index terms are equal.
if (dominating->length() != dominated->length()) {
return true;
}
SimpleLinearSum sumA = ExtractLinearSum(dominating->index());
SimpleLinearSum sumB = ExtractLinearSum(dominated->index());
// Both terms should be nullptr or the same definition.
if (sumA.term != sumB.term) {
return true;
}
// This bounds check is redundant.
*eliminated = true;
// Normalize the ranges according to the constant offsets in the two indexes.
int32_t minimumA, maximumA, minimumB, maximumB;
if (!SafeAdd(sumA.constant, dominating->minimum(), &minimumA) ||
!SafeAdd(sumA.constant, dominating->maximum(), &maximumA) ||
!SafeAdd(sumB.constant, dominated->minimum(), &minimumB) ||
!SafeAdd(sumB.constant, dominated->maximum(), &maximumB)) {
return false;
}
// Update the dominating check to cover both ranges, denormalizing the
// result per the constant offset in the index.
int32_t newMinimum, newMaximum;
if (!SafeSub(std::min(minimumA, minimumB), sumA.constant, &newMinimum) ||
!SafeSub(std::max(maximumA, maximumB), sumA.constant, &newMaximum)) {
return false;
}
dominating->setMinimum(newMinimum);
dominating->setMaximum(newMaximum);
dominating->setBailoutKind(BailoutKind::HoistBoundsCheck);
return true;
}
// Eliminate checks which are redundant given each other or other instructions.
//
// A bounds check is considered redundant if it's dominated by another bounds
// check with the same length and the indexes differ by only a constant amount.
// In this case we eliminate the redundant bounds check and update the other one
// to cover the ranges of both checks.
//
// Bounds checks are added to a hash map and since the hash function ignores
// differences in constant offset, this offers a fast way to find redundant
// checks.
bool jit::EliminateRedundantChecks(MIRGraph& graph) {
BoundsCheckMap checks(graph.alloc());
// Stack for pre-order CFG traversal.
Vector<MBasicBlock*, 1, JitAllocPolicy> worklist(graph.alloc());
// The index of the current block in the CFG traversal.
size_t index = 0;
// Add all self-dominating blocks to the worklist.
// This includes all roots. Order does not matter.
for (MBasicBlockIterator i(graph.begin()); i != graph.end(); i++) {
MBasicBlock* block = *i;
if (block->immediateDominator() == block) {
if (!worklist.append(block)) {
return false;
}
}
}
// Starting from each self-dominating block, traverse the CFG in pre-order.
while (!worklist.empty()) {
MBasicBlock* block = worklist.popCopy();
// Add all immediate dominators to the front of the worklist.
if (!worklist.append(block->immediatelyDominatedBlocksBegin(),
block->immediatelyDominatedBlocksEnd())) {
return false;
}
for (MDefinitionIterator iter(block); iter;) {
MDefinition* def = *iter++;
if (!def->isBoundsCheck()) {
continue;
}
auto* boundsCheck = def->toBoundsCheck();
bool eliminated = false;
if (!TryEliminateBoundsCheck(checks, index, boundsCheck, &eliminated)) {
return false;
}
if (eliminated) {
block->discard(boundsCheck);
}
}
index++;
}
MOZ_ASSERT(index == graph.numBlocks());
return true;
}
static bool ShapeGuardIsRedundant(MGuardShape* guard,
const MDefinition* storeObject,
const Shape* storeShape) {
const MDefinition* guardObject = guard->object()->skipObjectGuards();
if (guardObject != storeObject) {
JitSpew(JitSpew_RedundantShapeGuards, "SKIP: different objects (%d vs %d)",
guardObject->id(), storeObject->id());
return false;
}
const Shape* guardShape = guard->shape();
if (guardShape != storeShape) {
JitSpew(JitSpew_RedundantShapeGuards, "SKIP: different shapes");
return false;
}
return true;
}
// Eliminate shape guards which are redundant given other instructions.
//
// A shape guard is redundant if we can prove that the object being
// guarded already has the correct shape. The conditions for doing so
// are as follows:
//
// 1. We can see the most recent change to the shape of this object.
// (This can be an AddAndStoreSlot, an AllocateAndStoreSlot, or the
// creation of the object itself.
// 2. That mutation dominates the shape guard.
// 3. The shape that was assigned at that point matches the shape
// we expect.
//
// If all of these conditions hold, then we can remove the shape guard.
// In debug, we replace it with an AssertShape to help verify correctness.
bool jit::EliminateRedundantShapeGuards(MIRGraph& graph) {
JitSpew(JitSpew_RedundantShapeGuards, "Begin");
for (ReversePostorderIterator block = graph.rpoBegin();
block != graph.rpoEnd(); block++) {
for (MInstructionIterator insIter(block->begin());
insIter != block->end();) {
MInstruction* ins = *insIter;
insIter++;
// Skip instructions that aren't shape guards.
if (!ins->isGuardShape()) {
continue;
}
MGuardShape* guard = ins->toGuardShape();
MDefinition* lastStore = guard->dependency();
JitSpew(JitSpew_RedundantShapeGuards, "Visit shape guard %d",
guard->id());
JitSpewIndent spewIndent(JitSpew_RedundantShapeGuards);
if (lastStore->isDiscarded() || lastStore->block()->isDead() ||
!lastStore->block()->dominates(guard->block())) {
JitSpew(JitSpew_RedundantShapeGuards,
"SKIP: ins %d does not dominate block %d", lastStore->id(),
guard->block()->id());
continue;
}
if (lastStore->isAddAndStoreSlot()) {
auto* add = lastStore->toAddAndStoreSlot();
auto* addObject = add->object()->skipObjectGuards();
if (!ShapeGuardIsRedundant(guard, addObject, add->shape())) {
continue;
}
} else if (lastStore->isAllocateAndStoreSlot()) {
auto* allocate = lastStore->toAllocateAndStoreSlot();
auto* allocateObject = allocate->object()->skipObjectGuards();
if (!ShapeGuardIsRedundant(guard, allocateObject, allocate->shape())) {
continue;
}
} else if (lastStore->isStart()) {
// The guard doesn't depend on any other instruction that is modifying
// the object operand, so we check the object operand directly.
auto* obj = guard->object()->skipObjectGuards();
const Shape* initialShape = nullptr;
if (obj->isNewObject()) {
auto* templateObject = obj->toNewObject()->templateObject();
if (!templateObject) {
JitSpew(JitSpew_RedundantShapeGuards, "SKIP: no template");
continue;
}
initialShape = templateObject->shape();
} else if (obj->isNewPlainObject()) {
initialShape = obj->toNewPlainObject()->shape();
} else {
JitSpew(JitSpew_RedundantShapeGuards,
"SKIP: not NewObject or NewPlainObject (%d)", obj->id());
continue;
}
if (initialShape != guard->shape()) {
JitSpew(JitSpew_RedundantShapeGuards, "SKIP: shapes don't match");
continue;
}
} else {
JitSpew(JitSpew_RedundantShapeGuards,
"SKIP: Last store not supported (%d)", lastStore->id());
continue;
}
#ifdef DEBUG
if (!graph.alloc().ensureBallast()) {
return false;
}
auto* assert = MAssertShape::New(graph.alloc(), guard->object(),
const_cast<Shape*>(guard->shape()));
guard->block()->insertBefore(guard, assert);
#endif
JitSpew(JitSpew_RedundantShapeGuards, "SUCCESS: Removing shape guard %d",
guard->id());
guard->replaceAllUsesWith(guard->input());
guard->block()->discard(guard);
}
}
return true;
}
[[nodiscard]] static bool TryEliminateGCBarriersForAllocation(
TempAllocator& alloc, MInstruction* allocation) {
MOZ_ASSERT(allocation->type() == MIRType::Object);
JitSpew(JitSpew_RedundantGCBarriers, "Analyzing allocation %s",
allocation->opName());
MBasicBlock* block = allocation->block();
MInstructionIterator insIter(block->begin(allocation));
// Skip `allocation`.
MOZ_ASSERT(*insIter == allocation);
insIter++;
// Try to optimize the other instructions in the block.
while (insIter != block->end()) {
MInstruction* ins = *insIter;
insIter++;
switch (ins->op()) {
case MDefinition::Opcode::Constant:
case MDefinition::Opcode::Box:
case MDefinition::Opcode::Unbox:
case MDefinition::Opcode::AssertCanElidePostWriteBarrier:
// These instructions can't trigger GC or affect this analysis in other
// ways.
break;
case MDefinition::Opcode::StoreFixedSlot: {
auto* store = ins->toStoreFixedSlot();
if (store->object() != allocation) {
JitSpew(JitSpew_RedundantGCBarriers,
"Stopped at StoreFixedSlot for other object");
return true;
}
store->setNeedsBarrier(false);
JitSpew(JitSpew_RedundantGCBarriers, "Elided StoreFixedSlot barrier");
break;
}
case MDefinition::Opcode::PostWriteBarrier: {
auto* barrier = ins->toPostWriteBarrier();
if (barrier->object() != allocation) {
JitSpew(JitSpew_RedundantGCBarriers,
"Stopped at PostWriteBarrier for other object");
return true;
}
#ifdef DEBUG
if (!alloc.ensureBallast()) {
return false;
}
MDefinition* value = barrier->value();
if (value->type() != MIRType::Value) {
value = MBox::New(alloc, value);
block->insertBefore(barrier, value->toInstruction());
}
auto* assert =
MAssertCanElidePostWriteBarrier::New(alloc, allocation, value);
block->insertBefore(barrier, assert);
#endif
block->discard(barrier);
JitSpew(JitSpew_RedundantGCBarriers, "Elided PostWriteBarrier");
break;
}
default:
JitSpew(JitSpew_RedundantGCBarriers,
"Stopped at unsupported instruction %s", ins->opName());
return true;
}
}
return true;
}
bool jit::EliminateRedundantGCBarriers(MIRGraph& graph) {
// Peephole optimization for the following pattern:
//
// 0: MNewCallObject
// 1: MStoreFixedSlot(0, ...)
// 2: MStoreFixedSlot(0, ...)
// 3: MPostWriteBarrier(0, ...)
//
// If the instructions immediately following the allocation instruction can't
// trigger GC and we are storing to the new object's slots, we can elide the
// pre-barrier.
//
// We also eliminate the post barrier and (in debug builds) replace it with an
// assertion.
//
// See also the similar optimizations in WarpBuilder::buildCallObject.
JitSpew(JitSpew_RedundantGCBarriers, "Begin");
for (ReversePostorderIterator block = graph.rpoBegin();
block != graph.rpoEnd(); block++) {
for (MInstructionIterator insIter(block->begin());
insIter != block->end(); insIter++) {
MInstruction* ins = *insIter;
if (ins->isNewCallObject()) {
MNewCallObject* allocation = ins->toNewCallObject();
// We can only eliminate the post barrier if we know the call object
// will be allocated in the nursery.
if (allocation->initialHeap() == gc::Heap::Default) {
if (!TryEliminateGCBarriersForAllocation(graph.alloc(), allocation)) {
return false;
}
}
}
}
}
return true;
}
bool jit::MarkLoadsUsedAsPropertyKeys(MIRGraph& graph) {
// When a string is used as a property key, or as the key for a Map or Set, we
// require it to be atomized. To avoid repeatedly atomizing the same string,
// this analysis looks for cases where we are loading a value from the slot of
// an object (which includes access to global variables and global lexicals)
// and using it as a property key, and marks those loads. During codegen,
// marked loads will check whether the value loaded is a non-atomized string.
// If it is, we will atomize the string and update the stored value, ensuring
// that future loads from the same slot will not have to atomize again.
JitSpew(JitSpew_MarkLoadsUsedAsPropertyKeys, "Begin");
for (ReversePostorderIterator block = graph.rpoBegin();
block != graph.rpoEnd(); block++) {
for (MInstructionIterator insIter(block->begin());
insIter != block->end();) {
MInstruction* ins = *insIter;
insIter++;
MDefinition* idVal = nullptr;
if (ins->isGetPropertyCache()) {
idVal = ins->toGetPropertyCache()->idval();
} else if (ins->isHasOwnCache()) {
idVal = ins->toHasOwnCache()->idval();
} else if (ins->isSetPropertyCache()) {
idVal = ins->toSetPropertyCache()->idval();
} else if (ins->isGetPropSuperCache()) {
idVal = ins->toGetPropSuperCache()->idval();
} else if (ins->isMegamorphicLoadSlotByValue()) {
idVal = ins->toMegamorphicLoadSlotByValue()->idVal();
} else if (ins->isMegamorphicHasProp()) {
idVal = ins->toMegamorphicHasProp()->idVal();
} else if (ins->isMegamorphicSetElement()) {
idVal = ins->toMegamorphicSetElement()->index();
} else if (ins->isProxyGetByValue()) {
idVal = ins->toProxyGetByValue()->idVal();
} else if (ins->isProxyHasProp()) {
idVal = ins->toProxyHasProp()->idVal();
} else if (ins->isProxySetByValue()) {
idVal = ins->toProxySetByValue()->idVal();
} else if (ins->isIdToStringOrSymbol()) {
idVal = ins->toIdToStringOrSymbol()->idVal();
} else if (ins->isGuardSpecificAtom()) {
idVal = ins->toGuardSpecificAtom()->input();
} else if (ins->isToHashableString()) {
idVal = ins->toToHashableString()->input();
} else if (ins->isToHashableValue()) {
idVal = ins->toToHashableValue()->input();
} else if (ins->isMapObjectHasValueVMCall()) {
idVal = ins->toMapObjectHasValueVMCall()->value();
} else if (ins->isMapObjectGetValueVMCall()) {
idVal = ins->toMapObjectGetValueVMCall()->value();
} else if (ins->isSetObjectHasValueVMCall()) {
idVal = ins->toSetObjectHasValueVMCall()->value();
} else {
continue;
}
JitSpew(JitSpew_MarkLoadsUsedAsPropertyKeys,
"Analyzing property access %s%d with idVal %s%d", ins->opName(),
ins->id(), idVal->opName(), idVal->id());
// Skip intermediate nodes.
do {
if (idVal->isLexicalCheck()) {
idVal = idVal->toLexicalCheck()->input();
JitSpew(JitSpew_MarkLoadsUsedAsPropertyKeys,
"- Skipping lexical check. idVal is now %s%d",
idVal->opName(), idVal->id());
continue;
}
if (idVal->isUnbox() && idVal->type() == MIRType::String) {
idVal = idVal->toUnbox()->input();
JitSpew(JitSpew_MarkLoadsUsedAsPropertyKeys,
"- Skipping unbox. idVal is now %s%d", idVal->opName(),
idVal->id());
continue;
}
break;
} while (true);
if (idVal->isLoadFixedSlot()) {
JitSpew(JitSpew_MarkLoadsUsedAsPropertyKeys,
"- SUCCESS: Marking fixed slot");
idVal->toLoadFixedSlot()->setUsedAsPropertyKey();
} else if (idVal->isLoadDynamicSlot()) {
JitSpew(JitSpew_MarkLoadsUsedAsPropertyKeys,
"- SUCCESS: Marking dynamic slot");
idVal->toLoadDynamicSlot()->setUsedAsPropertyKey();
} else {
JitSpew(JitSpew_MarkLoadsUsedAsPropertyKeys, "- SKIP: %s not supported",
idVal->opName());
}
}
}
return true;
}
// Since wasm has a fairly rich type system enforced in validation, we can use
// this type system within MIR to robustly track the types of ref values. This
// allows us to make MIR-level optimizations such as eliding null checks or
// omitting redundant casts.
//
// This analysis pass performs simple data flow analysis by assigning ref types
// to each definition, then revisiting phis and their uses as necessary until
// the types have narrowed to a fixed point.
bool jit::TrackWasmRefTypes(MIRGraph& graph) {
// The worklist tracks nodes whose types have changed and whose uses must
// therefore be re-evaluated.
Vector<MDefinition*, 16, SystemAllocPolicy> worklist;
// Assign an initial ref type to each definition. Reverse postorder ensures
// that nodes are always visited before their uses, with the exception of loop
// backedge phis.
for (ReversePostorderIterator blockIter = graph.rpoBegin();
blockIter != graph.rpoEnd(); blockIter++) {
MBasicBlock* block = *blockIter;
for (MDefinitionIterator def(block); def; def++) {
// Set the initial type on all nodes. If a type is produced, then any
// loop backedge phis that use this node must have been previously
// visited, and must be updated and possibly added to the worklist. (Any
// other uses of this node will be visited later in this first pass.)
if (def->type() != MIRType::WasmAnyRef) {
continue;
}
bool hasType = def->updateWasmRefType();
if (hasType) {
for (MUseIterator use(def->usesBegin()); use != def->usesEnd(); use++) {
MNode* consumer = use->consumer();
if (!consumer->isDefinition() || !consumer->toDefinition()->isPhi()) {
continue;
}
MPhi* phi = consumer->toDefinition()->toPhi();
if (phi->block()->isLoopHeader() &&
*def == phi->getLoopBackedgeOperand()) {
bool changed = phi->updateWasmRefType();
if (changed && !worklist.append(phi)) {
return false;
}
} else {
// Any other type of use must not have a ref type yet, because we
// are yet to hit it in this forward pass.
MOZ_ASSERT(consumer->toDefinition()->wasmRefType().isNothing());
}
}
}
}
}
// Until the worklist is empty, update the uses of any worklist nodes and
// track the ones whose types change.
while (!worklist.empty()) {
MDefinition* def = worklist.popCopy();
for (MUseIterator use(def->usesBegin()); use != def->usesEnd(); use++) {
if (!use->consumer()->isDefinition()) {
continue;
}
bool changed = use->consumer()->toDefinition()->updateWasmRefType();
if (changed && !worklist.append(use->consumer()->toDefinition())) {
return false;
}
}
}
return true;
}
static bool NeedsKeepAlive(MInstruction* slotsOrElements, MInstruction* use) {
MOZ_ASSERT(slotsOrElements->type() == MIRType::Elements ||
slotsOrElements->type() == MIRType::Slots);
if (slotsOrElements->block() != use->block()) {
return true;
}
// Allocating a BigInt can GC, so we have to keep the object alive.
if (use->type() == MIRType::BigInt) {
return true;
}
if (use->isLoadTypedArrayElementHole() &&
Scalar::isBigIntType(use->toLoadTypedArrayElementHole()->arrayType())) {
return true;
}
MBasicBlock* block = use->block();
MInstructionIterator iter(block->begin(slotsOrElements));
MOZ_ASSERT(*iter == slotsOrElements);
++iter;
while (true) {
if (*iter == use) {
return false;
}
switch (iter->op()) {
case MDefinition::Opcode::Nop:
case MDefinition::Opcode::Constant:
case MDefinition::Opcode::KeepAliveObject:
case MDefinition::Opcode::Unbox:
case MDefinition::Opcode::LoadDynamicSlot:
case MDefinition::Opcode::StoreDynamicSlot:
case MDefinition::Opcode::LoadFixedSlot:
case MDefinition::Opcode::StoreFixedSlot:
case MDefinition::Opcode::LoadElement:
case MDefinition::Opcode::LoadElementAndUnbox:
case MDefinition::Opcode::LoadElementHole:
case MDefinition::Opcode::StoreElement:
case MDefinition::Opcode::StoreHoleValueElement:
case MDefinition::Opcode::InitializedLength:
case MDefinition::Opcode::ArrayLength:
case MDefinition::Opcode::BoundsCheck:
case MDefinition::Opcode::GuardElementNotHole:
case MDefinition::Opcode::InArray:
case MDefinition::Opcode::SpectreMaskIndex:
case MDefinition::Opcode::DebugEnterGCUnsafeRegion:
case MDefinition::Opcode::DebugLeaveGCUnsafeRegion:
iter++;
break;
default:
return true;
}
}
MOZ_CRASH("Unreachable");
}
bool jit::AddKeepAliveInstructions(MIRGraph& graph) {
for (MBasicBlockIterator i(graph.begin()); i != graph.end(); i++) {
MBasicBlock* block = *i;
for (MInstructionIterator insIter(block->begin()); insIter != block->end();
insIter++) {
MInstruction* ins = *insIter;
if (ins->type() != MIRType::Elements && ins->type() != MIRType::Slots) {
continue;
}
MDefinition* ownerObject;
switch (ins->op()) {
case MDefinition::Opcode::Elements:
case MDefinition::Opcode::ArrayBufferViewElements:
MOZ_ASSERT(ins->numOperands() == 1);
ownerObject = ins->getOperand(0);
break;
case MDefinition::Opcode::Slots:
ownerObject = ins->toSlots()->object();
break;
default:
MOZ_CRASH("Unexpected op");
}
MOZ_ASSERT(ownerObject->type() == MIRType::Object);
if (ownerObject->isConstant()) {
// Constants are kept alive by other pointers, for instance
// ImmGCPtr in JIT code.
continue;
}
for (MUseDefIterator uses(ins); uses; uses++) {
MInstruction* use = uses.def()->toInstruction();
if (use->isStoreElementHole()) {
// StoreElementHole has an explicit object operand. If GVN
// is disabled, we can get different unbox instructions with
// the same object as input, so we check for that case.
MOZ_ASSERT_IF(!use->toStoreElementHole()->object()->isUnbox() &&
!ownerObject->isUnbox(),
use->toStoreElementHole()->object() == ownerObject);
continue;
}
if (!NeedsKeepAlive(ins, use)) {
#ifdef DEBUG
// These two instructions don't start a GC unsafe region, because they
// overwrite their elements register at the very start. This ensures
// there's no invalidated elements value kept on the stack.
if (use->isApplyArray() || use->isConstructArray()) {
continue;
}
if (!graph.alloc().ensureBallast()) {
return false;
}
// Enter a GC unsafe region while the elements/slots are on the stack.
auto* enter = MDebugEnterGCUnsafeRegion::New(graph.alloc());
use->block()->insertAfter(ins, enter);
// Leave the region after the use.
auto* leave = MDebugLeaveGCUnsafeRegion::New(graph.alloc());
use->block()->insertAfter(use, leave);
#endif
continue;
}
if (!graph.alloc().ensureBallast()) {
return false;
}
MKeepAliveObject* keepAlive =
MKeepAliveObject::New(graph.alloc(), ownerObject);
use->block()->insertAfter(use, keepAlive);
}
}
}
return true;
}
bool LinearSum::multiply(int32_t scale) {
for (size_t i = 0; i < terms_.length(); i++) {
if (!SafeMul(scale, terms_[i].scale, &terms_[i].scale)) {
return false;
}
}
return SafeMul(scale, constant_, &constant_);
}
bool LinearSum::divide(uint32_t scale) {
MOZ_ASSERT(scale > 0);
for (size_t i = 0; i < terms_.length(); i++) {
if (terms_[i].scale % scale != 0) {
return false;
}
}
if (constant_ % scale != 0) {
return false;
}
for (size_t i = 0; i < terms_.length(); i++) {
terms_[i].scale /= scale;
}
constant_ /= scale;
return true;
}
bool LinearSum::add(const LinearSum& other, int32_t scale /* = 1 */) {
for (size_t i = 0; i < other.terms_.length(); i++) {
int32_t newScale = scale;
if (!SafeMul(scale, other.terms_[i].scale, &newScale)) {
return false;
}
if (!add(other.terms_[i].term, newScale)) {
return false;
}
}
int32_t newConstant = scale;
if (!SafeMul(scale, other.constant_, &newConstant)) {
return false;
}
return add(newConstant);
}
bool LinearSum::add(SimpleLinearSum other, int32_t scale) {
if (other.term && !add(other.term, scale)) {
return false;
}
int32_t constant;
if (!SafeMul(other.constant, scale, &constant)) {
return false;
}
return add(constant);
}
bool LinearSum::add(MDefinition* term, int32_t scale) {
MOZ_ASSERT(term);
if (scale == 0) {
return true;
}
if (MConstant* termConst = term->maybeConstantValue()) {
int32_t constant = termConst->toInt32();
if (!SafeMul(constant, scale, &constant)) {
return false;
}
return add(constant);
}
for (size_t i = 0; i < terms_.length(); i++) {
if (term == terms_[i].term) {
if (!SafeAdd(scale, terms_[i].scale, &terms_[i].scale)) {
return false;
}
if (terms_[i].scale == 0) {
terms_[i] = terms_.back();
terms_.popBack();
}
return true;
}
}
AutoEnterOOMUnsafeRegion oomUnsafe;
if (!terms_.append(LinearTerm(term, scale))) {
oomUnsafe.crash("LinearSum::add");
}
return true;
}
bool LinearSum::add(int32_t constant) {
return SafeAdd(constant, constant_, &constant_);
}
void LinearSum::dump(GenericPrinter& out) const {
for (size_t i = 0; i < terms_.length(); i++) {
int32_t scale = terms_[i].scale;
int32_t id = terms_[i].term->id();
MOZ_ASSERT(scale);
if (scale > 0) {
if (i) {
out.printf("+");
}
if (scale == 1) {
out.printf("#%d", id);
} else {
out.printf("%d*#%d", scale, id);
}
} else if (scale == -1) {
out.printf("-#%d", id);
} else {
out.printf("%d*#%d", scale, id);
}
}
if (constant_ > 0) {
out.printf("+%d", constant_);
} else if (constant_ < 0) {
out.printf("%d", constant_);
}
}
void LinearSum::dump() const {
Fprinter out(stderr);
dump(out);
out.finish();
}
MDefinition* jit::ConvertLinearSum(TempAllocator& alloc, MBasicBlock* block,
const LinearSum& sum,
BailoutKind bailoutKind) {
MDefinition* def = nullptr;
for (size_t i = 0; i < sum.numTerms(); i++) {
LinearTerm term = sum.term(i);
MOZ_ASSERT(!term.term->isConstant());
if (term.scale == 1) {
if (def) {
def = MAdd::New(alloc, def, term.term, MIRType::Int32);
def->setBailoutKind(bailoutKind);
block->insertAtEnd(def->toInstruction());
def->computeRange(alloc);
} else {
def = term.term;
}
} else if (term.scale == -1) {
if (!def) {
def = MConstant::New(alloc, Int32Value(0));
block->insertAtEnd(def->toInstruction());
def->computeRange(alloc);
}
def = MSub::New(alloc, def, term.term, MIRType::Int32);
def->setBailoutKind(bailoutKind);
block->insertAtEnd(def->toInstruction());
def->computeRange(alloc);
} else {
MOZ_ASSERT(term.scale != 0);
MConstant* factor = MConstant::New(alloc, Int32Value(term.scale));
block->insertAtEnd(factor);
MMul* mul = MMul::New(alloc, term.term, factor, MIRType::Int32);
mul->setBailoutKind(bailoutKind);
block->insertAtEnd(mul);
mul->computeRange(alloc);
if (def) {
def = MAdd::New(alloc, def, mul, MIRType::Int32);
def->setBailoutKind(bailoutKind);
block->insertAtEnd(def->toInstruction());
def->computeRange(alloc);
} else {
def = mul;
}
}
}
if (!def) {
def = MConstant::New(alloc, Int32Value(0));
block->insertAtEnd(def->toInstruction());
def->computeRange(alloc);
}
return def;
}
// Mark all the blocks that are in the loop with the given header.
// Returns the number of blocks marked. Set *canOsr to true if the loop is
// reachable from both the normal entry and the OSR entry.
size_t jit::MarkLoopBlocks(MIRGraph& graph, const MBasicBlock* header,
bool* canOsr) {
#ifdef DEBUG
for (ReversePostorderIterator i = graph.rpoBegin(), e = graph.rpoEnd();
i != e; ++i) {
MOZ_ASSERT(!i->isMarked(), "Some blocks already marked");
}
#endif
MBasicBlock* osrBlock = graph.osrBlock();
*canOsr = false;
// The blocks are in RPO; start at the loop backedge, which marks the bottom
// of the loop, and walk up until we get to the header. Loops may be
// discontiguous, so we trace predecessors to determine which blocks are
// actually part of the loop. The backedge is always part of the loop, and
// so are its predecessors, transitively, up to the loop header or an OSR
// entry.
MBasicBlock* backedge = header->backedge();
backedge->mark();
size_t numMarked = 1;
for (PostorderIterator i = graph.poBegin(backedge);; ++i) {
MOZ_ASSERT(
i != graph.poEnd(),
"Reached the end of the graph while searching for the loop header");
MBasicBlock* block = *i;
// If we've reached the loop header, we're done.
if (block == header) {
break;
}
// A block not marked by the time we reach it is not in the loop.
if (!block->isMarked()) {
continue;
}
// This block is in the loop; trace to its predecessors.
for (size_t p = 0, e = block->numPredecessors(); p != e; ++p) {
MBasicBlock* pred = block->getPredecessor(p);
if (pred->isMarked()) {
continue;
}
// Blocks dominated by the OSR entry are not part of the loop
// (unless they aren't reachable from the normal entry).
if (osrBlock && pred != header && osrBlock->dominates(pred) &&
!osrBlock->dominates(header)) {
*canOsr = true;
continue;
}
MOZ_ASSERT(pred->id() >= header->id() && pred->id() <= backedge->id(),
"Loop block not between loop header and loop backedge");
pred->mark();
++numMarked;
// A nested loop may not exit back to the enclosing loop at its
// bottom. If we just marked its header, then the whole nested loop
// is part of the enclosing loop.
if (pred->isLoopHeader()) {
MBasicBlock* innerBackedge = pred->backedge();
if (!innerBackedge->isMarked()) {
// Mark its backedge so that we add all of its blocks to the
// outer loop as we walk upwards.
innerBackedge->mark();
++numMarked;
// If the nested loop is not contiguous, we may have already
// passed its backedge. If this happens, back up.
if (innerBackedge->id() > block->id()) {
i = graph.poBegin(innerBackedge);
--i;
}
}
}
}
}
// If there's no path connecting the header to the backedge, then this isn't
// actually a loop. This can happen when the code starts with a loop but GVN
// folds some branches away.
if (!header->isMarked()) {
jit::UnmarkLoopBlocks(graph, header);
return 0;
}
return numMarked;
}
// Unmark all the blocks that are in the loop with the given header.
void jit::UnmarkLoopBlocks(MIRGraph& graph, const MBasicBlock* header) {
MBasicBlock* backedge = header->backedge();
for (ReversePostorderIterator i = graph.rpoBegin(header);; ++i) {
MOZ_ASSERT(i != graph.rpoEnd(),
"Reached the end of the graph while searching for the backedge");
MBasicBlock* block = *i;
if (block->isMarked()) {
block->unmark();
if (block == backedge) {
break;
}
}
}
#ifdef DEBUG
for (ReversePostorderIterator i = graph.rpoBegin(), e = graph.rpoEnd();
i != e; ++i) {
MOZ_ASSERT(!i->isMarked(), "Not all blocks got unmarked");
}
#endif
}
bool jit::FoldLoadsWithUnbox(const MIRGenerator* mir, MIRGraph& graph) {
// This pass folds MLoadFixedSlot, MLoadDynamicSlot, MLoadElement instructions
// followed by MUnbox into a single instruction. For LoadElement this allows
// us to fuse the hole check with the type check for the unbox.
for (MBasicBlockIterator block(graph.begin()); block != graph.end();
block++) {
if (mir->shouldCancel("FoldLoadsWithUnbox")) {
return false;
}
for (MInstructionIterator insIter(block->begin());
insIter != block->end();) {
MInstruction* ins = *insIter;
insIter++;
// We're only interested in loads producing a Value.
if (!ins->isLoadFixedSlot() && !ins->isLoadDynamicSlot() &&
!ins->isLoadElement()) {
continue;
}
if (ins->type() != MIRType::Value) {
continue;
}
MInstruction* load = ins;
// Ensure there's a single def-use (ignoring resume points) and it's an
// unbox. Unwrap MLexicalCheck because it's redundant if we have a
// fallible unbox (checked below).
MDefinition* defUse = load->maybeSingleDefUse();
if (!defUse) {
continue;
}
MLexicalCheck* lexicalCheck = nullptr;
if (defUse->isLexicalCheck()) {
lexicalCheck = defUse->toLexicalCheck();
defUse = lexicalCheck->maybeSingleDefUse();
if (!defUse) {
continue;
}
}
if (!defUse->isUnbox()) {
continue;
}
// For now require the load and unbox to be in the same block. This isn't
// strictly necessary but it's the common case and could prevent bailouts
// when moving the unbox before a loop.
MUnbox* unbox = defUse->toUnbox();
if (unbox->block() != *block) {
continue;
}
MOZ_ASSERT_IF(lexicalCheck, lexicalCheck->block() == *block);
MOZ_ASSERT(!IsMagicType(unbox->type()));
// If this is a LoadElement or if we have a lexical check between the load
// and unbox, we only support folding the load with a fallible unbox so
// that we can eliminate the MagicValue check.
if ((load->isLoadElement() || lexicalCheck) && !unbox->fallible()) {
continue;
}
// Combine the load and unbox into a single MIR instruction.
if (!graph.alloc().ensureBallast()) {
return false;
}
MIRType type = unbox->type();
MUnbox::Mode mode = unbox->mode();
MInstruction* replacement;
switch (load->op()) {
case MDefinition::Opcode::LoadFixedSlot: {
auto* loadIns = load->toLoadFixedSlot();
replacement = MLoadFixedSlotAndUnbox::New(
graph.alloc(), loadIns->object(), loadIns->slot(), mode, type,
loadIns->usedAsPropertyKey());
break;
}
case MDefinition::Opcode::LoadDynamicSlot: {
auto* loadIns = load->toLoadDynamicSlot();
replacement = MLoadDynamicSlotAndUnbox::New(
graph.alloc(), loadIns->slots(), loadIns->slot(), mode, type,
loadIns->usedAsPropertyKey());
break;
}
case MDefinition::Opcode::LoadElement: {
auto* loadIns = load->toLoadElement();
MOZ_ASSERT(unbox->fallible());
replacement = MLoadElementAndUnbox::New(
graph.alloc(), loadIns->elements(), loadIns->index(), mode, type);
break;
}
default:
MOZ_CRASH("Unexpected instruction");
}
replacement->setBailoutKind(BailoutKind::UnboxFolding);
block->insertBefore(load, replacement);
unbox->replaceAllUsesWith(replacement);
if (lexicalCheck) {
lexicalCheck->replaceAllUsesWith(replacement);
}
load->replaceAllUsesWith(replacement);
if (lexicalCheck && *insIter == lexicalCheck) {
insIter++;
}
if (*insIter == unbox) {
insIter++;
}
block->discard(unbox);
if (lexicalCheck) {
block->discard(lexicalCheck);
}
block->discard(load);
}
}
return true;
}
// Reorder the blocks in the loop starting at the given header to be contiguous.
static void MakeLoopContiguous(MIRGraph& graph, MBasicBlock* header,
size_t numMarked) {
MBasicBlock* backedge = header->backedge();
MOZ_ASSERT(header->isMarked(), "Loop header is not part of loop");
MOZ_ASSERT(backedge->isMarked(), "Loop backedge is not part of loop");
// If there are any blocks between the loop header and the loop backedge
// that are not part of the loop, prepare to move them to the end. We keep
// them in order, which preserves RPO.
ReversePostorderIterator insertIter = graph.rpoBegin(backedge);
insertIter++;
MBasicBlock* insertPt = *insertIter;
// Visit all the blocks from the loop header to the loop backedge.
size_t headerId = header->id();
size_t inLoopId = headerId;
size_t notInLoopId = inLoopId + numMarked;
ReversePostorderIterator i = graph.rpoBegin(header);
for (;;) {
MBasicBlock* block = *i++;
MOZ_ASSERT(block->id() >= header->id() && block->id() <= backedge->id(),
"Loop backedge should be last block in loop");
if (block->isMarked()) {
// This block is in the loop.
block->unmark();
block->setId(inLoopId++);
// If we've reached the loop backedge, we're done!
if (block == backedge) {
break;
}
} else {
// This block is not in the loop. Move it to the end.
graph.moveBlockBefore(insertPt, block);
block->setId(notInLoopId++);
}
}
MOZ_ASSERT(header->id() == headerId, "Loop header id changed");
MOZ_ASSERT(inLoopId == headerId + numMarked,
"Wrong number of blocks kept in loop");
MOZ_ASSERT(notInLoopId == (insertIter != graph.rpoEnd() ? insertPt->id()
: graph.numBlocks()),
"Wrong number of blocks moved out of loop");
}
// Reorder the blocks in the graph so that loops are contiguous.
bool jit::MakeLoopsContiguous(MIRGraph& graph) {
// Visit all loop headers (in any order).
for (MBasicBlockIterator i(graph.begin()); i != graph.end(); i++) {
MBasicBlock* header = *i;
if (!header->isLoopHeader()) {
continue;
}
// Mark all blocks that are actually part of the loop.
bool canOsr;
size_t numMarked = MarkLoopBlocks(graph, header, &canOsr);
// If the loop isn't a loop, don't try to optimize it.
if (numMarked == 0) {
continue;
}
// If there's an OSR block entering the loop in the middle, it's tricky,
// so don't try to handle it, for now.
if (canOsr) {
UnmarkLoopBlocks(graph, header);
continue;
}
// Move all blocks between header and backedge that aren't marked to
// the end of the loop, making the loop itself contiguous.
MakeLoopContiguous(graph, header, numMarked);
}
return true;
}
static MDefinition* SkipUnbox(MDefinition* ins) {
if (ins->isUnbox()) {
return ins->toUnbox()->input();
}
return ins;
}
bool jit::OptimizeIteratorIndices(const MIRGenerator* mir, MIRGraph& graph) {
bool changed = false;
for (ReversePostorderIterator blockIter = graph.rpoBegin();
blockIter != graph.rpoEnd();) {
MBasicBlock* block = *blockIter++;
for (MInstructionIterator insIter(block->begin());
insIter != block->end();) {
MInstruction* ins = *insIter;
insIter++;
if (!graph.alloc().ensureBallast()) {
return false;
}
MDefinition* receiver = nullptr;
MDefinition* idVal = nullptr;
MDefinition* setValue = nullptr;
if (ins->isMegamorphicHasProp() &&
ins->toMegamorphicHasProp()->hasOwn()) {
receiver = ins->toMegamorphicHasProp()->object();
idVal = ins->toMegamorphicHasProp()->idVal();
} else if (ins->isHasOwnCache()) {
receiver = ins->toHasOwnCache()->value();
idVal = ins->toHasOwnCache()->idval();
} else if (ins->isMegamorphicLoadSlotByValue()) {
receiver = ins->toMegamorphicLoadSlotByValue()->object();
idVal = ins->toMegamorphicLoadSlotByValue()->idVal();
} else if (ins->isGetPropertyCache()) {
receiver = ins->toGetPropertyCache()->value();
idVal = ins->toGetPropertyCache()->idval();
} else if (ins->isMegamorphicSetElement()) {
receiver = ins->toMegamorphicSetElement()->object();
idVal = ins->toMegamorphicSetElement()->index();
setValue = ins->toMegamorphicSetElement()->value();
} else if (ins->isSetPropertyCache()) {
receiver = ins->toSetPropertyCache()->object();
idVal = ins->toSetPropertyCache()->idval();
setValue = ins->toSetPropertyCache()->value();
}
if (!receiver) {
continue;
}
// Given the following structure (that occurs inside for-in loops):
// obj: some object
// iter: ObjectToIterator <obj>
// iterNext: IteratorMore <iter>
// access: HasProp/GetElem <obj> <iterNext>
// If the iterator object has an indices array, we can speed up the
// property access:
// 1. If the property access is a HasProp looking for own properties,
// then the result will always be true if the iterator has indices,
// because we only populate the indices array for objects with no
// enumerable properties on the prototype.
// 2. If the property access is a GetProp, then we can use the contents
// of the indices array to find the correct property faster than
// the megamorphic cache.
if (!idVal->isIteratorMore()) {
continue;
}
auto* iterNext = idVal->toIteratorMore();
if (!iterNext->iterator()->isObjectToIterator()) {
continue;
}
MObjectToIterator* iter = iterNext->iterator()->toObjectToIterator();
if (SkipUnbox(iter->object()) != SkipUnbox(receiver)) {
continue;
}
MInstruction* indicesCheck =
MIteratorHasIndices::New(graph.alloc(), iter->object(), iter);
MInstruction* replacement;
if (ins->isHasOwnCache() || ins->isMegamorphicHasProp()) {
MOZ_ASSERT(!setValue);
replacement = MConstant::New(graph.alloc(), BooleanValue(true));
} else if (ins->isMegamorphicLoadSlotByValue() ||
ins->isGetPropertyCache()) {
MOZ_ASSERT(!setValue);
replacement =
MLoadSlotByIteratorIndex::New(graph.alloc(), receiver, iter);
} else {
MOZ_ASSERT(ins->isMegamorphicSetElement() || ins->isSetPropertyCache());
MOZ_ASSERT(setValue);
replacement = MStoreSlotByIteratorIndex::New(graph.alloc(), receiver,
iter, setValue);
}
if (!block->wrapInstructionInFastpath(ins, replacement, indicesCheck)) {
return false;
}
iter->setWantsIndices(true);
changed = true;
// Advance to join block.
blockIter = graph.rpoBegin(block->getSuccessor(0)->getSuccessor(0));
break;
}
}
if (changed && !AccountForCFGChanges(mir, graph,
/*updateAliasAnalysis=*/false)) {
return false;
}
return true;
}
// =====================================================================
//
// Debug printing
void jit::DumpHashedPointer(GenericPrinter& out, const void* p) {
#ifdef JS_JITSPEW
if (!p) {
out.printf("NULL");
return;
}
char tab[27] = "abcdefghijklmnopqrstuvwxyz";
MOZ_ASSERT(tab[26] == '\0');
mozilla::HashNumber hash = mozilla::AddToHash(mozilla::HashNumber(0), p);
hash %= (26 * 26 * 26 * 26 * 26);
char buf[6];
for (int i = 0; i <= 4; i++) {
buf[i] = tab[hash % 26];
hash /= 26;
}
buf[5] = '\0';
out.printf("%s", buf);
#endif
}
void jit::DumpMIRDefinitionID(GenericPrinter& out, const MDefinition* def,
bool showHashedPointers) {
#ifdef JS_JITSPEW
if (!def) {
out.printf("(null)");
return;
}
if (showHashedPointers) {
DumpHashedPointer(out, def);
out.printf(".");
}
out.printf("%u", def->id());
#endif
}
void jit::DumpMIRDefinition(GenericPrinter& out, const MDefinition* def,
bool showHashedPointers) {
#ifdef JS_JITSPEW
DumpMIRDefinitionID(out, def, showHashedPointers);
out.printf(" = %s.", StringFromMIRType(def->type()));
if (def->isConstant()) {
def->printOpcode(out);
} else {
MDefinition::PrintOpcodeName(out, def->op());
}
// Get any extra bits of text that the MIR node wants to show us. Both the
// vector and the strings added to it belong to this function, so both will
// be automatically freed at exit.
ExtrasCollector extras;
def->getExtras(&extras);
for (size_t i = 0; i < extras.count(); i++) {
out.printf(" %s", extras.get(i).get());
}
for (size_t i = 0; i < def->numOperands(); i++) {
out.printf(" ");
DumpMIRDefinitionID(out, def->getOperand(i), showHashedPointers);
}
#endif
}
void jit::DumpMIRBlockID(GenericPrinter& out, const MBasicBlock* block,
bool showHashedPointers) {
#ifdef JS_JITSPEW
if (!block) {
out.printf("Block(null)");
return;
}
out.printf("Block");
if (showHashedPointers) {
out.printf(".");
DumpHashedPointer(out, block);
out.printf(".");
}
out.printf("%u", block->id());
#endif
}
void jit::DumpMIRBlock(GenericPrinter& out, MBasicBlock* block,
bool showHashedPointers) {
#ifdef JS_JITSPEW
out.printf(" ");
DumpMIRBlockID(out, block, showHashedPointers);
out.printf(" -- preds=[");
for (uint32_t i = 0; i < block->numPredecessors(); i++) {
MBasicBlock* pred = block->getPredecessor(i);
out.printf("%s", i == 0 ? "" : ", ");
DumpMIRBlockID(out, pred, showHashedPointers);
}
out.printf("] -- LD=%u -- K=%s -- s-w-phis=", block->loopDepth(),
block->nameOfKind());
if (block->successorWithPhis()) {
DumpMIRBlockID(out, block->successorWithPhis(), showHashedPointers);
out.printf(",#%u\n", block->positionInPhiSuccessor());
} else {
out.printf("(null)\n");
}
for (MPhiIterator iter(block->phisBegin()), end(block->phisEnd());
iter != end; iter++) {
out.printf(" ");
jit::DumpMIRDefinition(out, *iter, showHashedPointers);
out.printf("\n");
}
for (MInstructionIterator iter(block->begin()), end(block->end());
iter != end; iter++) {
out.printf(" ");
DumpMIRDefinition(out, *iter, showHashedPointers);
out.printf("\n");
}
#endif
}
void jit::DumpMIRGraph(GenericPrinter& out, MIRGraph& graph,
bool showHashedPointers) {
#ifdef JS_JITSPEW
for (ReversePostorderIterator block(graph.rpoBegin());
block != graph.rpoEnd(); block++) {
DumpMIRBlock(out, *block, showHashedPointers);
}
#endif
}
void jit::DumpMIRExpressions(GenericPrinter& out, MIRGraph& graph,
const CompileInfo& info, const char* phase,
bool showHashedPointers) {
#ifdef JS_JITSPEW
if (!JitSpewEnabled(JitSpew_MIRExpressions)) {
return;
}
out.printf("===== %s =====\n", phase);
DumpMIRGraph(out, graph, showHashedPointers);
if (info.compilingWasm()) {
out.printf("===== end wasm MIR dump =====\n");
} else {
out.printf("===== %s:%u =====\n", info.filename(), info.lineno());
}
#endif
}