Source code
Revision control
Copy as Markdown
Other Tools
/*
* Copyright © 2010 Intel Corporation
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the next
* paragraph) shall be included in all copies or substantial portions of the
* Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*/
#include "compiler/glsl_types.h"
#include "loop_analysis.h"
#include "ir_hierarchical_visitor.h"
#include "main/mtypes.h"
namespace {
class loop_unroll_visitor : public ir_hierarchical_visitor {
public:
loop_unroll_visitor(loop_state *state,
const struct gl_shader_compiler_options *options)
{
this->state = state;
this->progress = false;
this->options = options;
}
virtual ir_visitor_status visit_leave(ir_loop *ir);
void simple_unroll(ir_loop *ir, int iterations);
void complex_unroll(ir_loop *ir, int iterations,
bool continue_from_then_branch,
bool limiting_term_first,
bool lt_continue_from_then_branch);
void splice_post_if_instructions(ir_if *ir_if, exec_list *splice_dest);
loop_state *state;
bool progress;
const struct gl_shader_compiler_options *options;
};
} /* anonymous namespace */
class loop_unroll_count : public ir_hierarchical_visitor {
public:
int nodes;
bool unsupported_variable_indexing;
bool array_indexed_by_induction_var_with_exact_iterations;
/* If there are nested loops, the node count will be inaccurate. */
bool nested_loop;
loop_unroll_count(exec_list *list, loop_variable_state *ls,
const struct gl_shader_compiler_options *options)
: ls(ls), options(options)
{
nodes = 0;
nested_loop = false;
unsupported_variable_indexing = false;
array_indexed_by_induction_var_with_exact_iterations = false;
run(list);
}
virtual ir_visitor_status visit_enter(ir_assignment *)
{
nodes++;
return visit_continue;
}
virtual ir_visitor_status visit_enter(ir_expression *)
{
nodes++;
return visit_continue;
}
virtual ir_visitor_status visit_enter(ir_loop *)
{
nested_loop = true;
return visit_continue;
}
virtual ir_visitor_status visit_enter(ir_dereference_array *ir)
{
/* Force unroll in case of dynamic indexing with sampler arrays
* when EmitNoIndirectSampler is set.
*/
if (options->EmitNoIndirectSampler) {
if ((ir->array->type->is_array() &&
ir->array->type->contains_sampler()) &&
!ir->array_index->constant_expression_value(ralloc_parent(ir))) {
unsupported_variable_indexing = true;
return visit_continue;
}
}
/* Check for arrays variably-indexed by a loop induction variable.
* Unrolling the loop may convert that access into constant-indexing.
*
* Many drivers don't support particular kinds of variable indexing,
* and have to resort to using lower_variable_index_to_cond_assign to
* handle it. This results in huge amounts of horrible code, so we'd
* like to avoid that if possible. Here, we just note that it will
* happen.
*/
if ((ir->array->type->is_array() || ir->array->type->is_matrix()) &&
!ir->array_index->as_constant()) {
ir_variable *array = ir->array->variable_referenced();
loop_variable *lv = ls->get(ir->array_index->variable_referenced());
if (array && lv && lv->is_induction_var()) {
/* If an array is indexed by a loop induction variable, and the
* array size is exactly the number of loop iterations, this is
* probably a simple for-loop trying to access each element in
* turn; the application may expect it to be unrolled.
*/
if (int(array->type->length) == ls->limiting_terminator->iterations)
array_indexed_by_induction_var_with_exact_iterations = true;
switch (array->data.mode) {
case ir_var_auto:
case ir_var_temporary:
case ir_var_const_in:
case ir_var_function_in:
case ir_var_function_out:
case ir_var_function_inout:
if (options->EmitNoIndirectTemp)
unsupported_variable_indexing = true;
break;
case ir_var_uniform:
case ir_var_shader_storage:
if (options->EmitNoIndirectUniform)
unsupported_variable_indexing = true;
break;
case ir_var_shader_in:
if (options->EmitNoIndirectInput)
unsupported_variable_indexing = true;
break;
case ir_var_shader_out:
if (options->EmitNoIndirectOutput)
unsupported_variable_indexing = true;
break;
}
}
}
return visit_continue;
}
private:
loop_variable_state *ls;
const struct gl_shader_compiler_options *options;
};
/**
* Unroll a loop which does not contain any jumps. For example, if the input
* is:
*
* (loop (...) ...instrs...)
*
* And the iteration count is 3, the output will be:
*
* ...instrs... ...instrs... ...instrs...
*/
void
loop_unroll_visitor::simple_unroll(ir_loop *ir, int iterations)
{
void *const mem_ctx = ralloc_parent(ir);
loop_variable_state *const ls = this->state->get(ir);
/* If there are no terminators, then the loop iteration count must be 1.
* This is the 'do { } while (false);' case.
*/
assert(!ls->terminators.is_empty() || iterations == 1);
ir_instruction *first_ir =
(ir_instruction *) ir->body_instructions.get_head();
if (!first_ir) {
/* The loop is empty remove it and return */
ir->remove();
return;
}
ir_if *limit_if = NULL;
bool exit_branch_has_instructions = false;
if (ls->limiting_terminator) {
limit_if = ls->limiting_terminator->ir;
ir_instruction *ir_if_last = (ir_instruction *)
limit_if->then_instructions.get_tail();
if (is_break(ir_if_last)) {
if (ir_if_last != limit_if->then_instructions.get_head())
exit_branch_has_instructions = true;
splice_post_if_instructions(limit_if, &limit_if->else_instructions);
ir_if_last->remove();
} else {
ir_if_last = (ir_instruction *)
limit_if->else_instructions.get_tail();
assert(is_break(ir_if_last));
if (ir_if_last != limit_if->else_instructions.get_head())
exit_branch_has_instructions = true;
splice_post_if_instructions(limit_if, &limit_if->then_instructions);
ir_if_last->remove();
}
}
/* Because 'iterations' is the number of times we pass over the *entire*
* loop body before hitting the first break, we need to bump the number of
* iterations if the limiting terminator is not the first instruction in
* the loop, or it the exit branch contains instructions. This ensures we
* execute any instructions before the terminator or in its exit branch.
*/
if (!ls->terminators.is_empty() &&
(limit_if != first_ir->as_if() || exit_branch_has_instructions))
iterations++;
for (int i = 0; i < iterations; i++) {
exec_list copy_list;
copy_list.make_empty();
clone_ir_list(mem_ctx, ©_list, &ir->body_instructions);
ir->insert_before(©_list);
}
/* The loop has been replaced by the unrolled copies. Remove the original
* loop from the IR sequence.
*/
ir->remove();
this->progress = true;
}
/**
* Unroll a loop whose last statement is an ir_if. If \c
* continue_from_then_branch is true, the loop is repeated only when the
* "then" branch of the if is taken; otherwise it is repeated only when the
* "else" branch of the if is taken.
*
* For example, if the input is:
*
* (loop (...)
* ...body...
* (if (cond)
* (...then_instrs...)
* (...else_instrs...)))
*
* And the iteration count is 3, and \c continue_from_then_branch is true,
* then the output will be:
*
* ...body...
* (if (cond)
* (...then_instrs...
* ...body...
* (if (cond)
* (...then_instrs...
* ...body...
* (if (cond)
* (...then_instrs...)
* (...else_instrs...)))
* (...else_instrs...)))
* (...else_instrs))
*/
void
loop_unroll_visitor::complex_unroll(ir_loop *ir, int iterations,
bool second_term_then_continue,
bool extra_iteration_required,
bool first_term_then_continue)
{
void *const mem_ctx = ralloc_parent(ir);
ir_instruction *ir_to_replace = ir;
/* Because 'iterations' is the number of times we pass over the *entire*
* loop body before hitting the first break, we need to bump the number of
* iterations if the limiting terminator is not the first instruction in
* the loop, or it the exit branch contains instructions. This ensures we
* execute any instructions before the terminator or in its exit branch.
*/
if (extra_iteration_required)
iterations++;
for (int i = 0; i < iterations; i++) {
exec_list copy_list;
copy_list.make_empty();
clone_ir_list(mem_ctx, ©_list, &ir->body_instructions);
ir_if *ir_if = ((ir_instruction *) copy_list.get_tail())->as_if();
assert(ir_if != NULL);
exec_list *const first_list = first_term_then_continue
? &ir_if->then_instructions : &ir_if->else_instructions;
ir_if = ((ir_instruction *) first_list->get_tail())->as_if();
ir_to_replace->insert_before(©_list);
ir_to_replace->remove();
/* placeholder that will be removed in the next iteration */
ir_to_replace =
new(mem_ctx) ir_loop_jump(ir_loop_jump::jump_continue);
exec_list *const second_term_continue_list = second_term_then_continue
? &ir_if->then_instructions : &ir_if->else_instructions;
second_term_continue_list->push_tail(ir_to_replace);
}
ir_to_replace->remove();
this->progress = true;
}
/**
* Move all of the instructions which follow \c ir_if to the end of
* \c splice_dest.
*
* For example, in the code snippet:
*
* (if (cond)
* (...then_instructions...
* break)
* (...else_instructions...))
* ...post_if_instructions...
*
* If \c ir_if points to the "if" instruction, and \c splice_dest points to
* (...else_instructions...), the code snippet is transformed into:
*
* (if (cond)
* (...then_instructions...
* break)
* (...else_instructions...
* ...post_if_instructions...))
*/
void
loop_unroll_visitor::splice_post_if_instructions(ir_if *ir_if,
exec_list *splice_dest)
{
while (!ir_if->get_next()->is_tail_sentinel()) {
ir_instruction *move_ir = (ir_instruction *) ir_if->get_next();
move_ir->remove();
splice_dest->push_tail(move_ir);
}
}
static bool
exit_branch_has_instructions(ir_if *term_if, bool lt_then_continue)
{
if (lt_then_continue) {
if (term_if->else_instructions.get_head() ==
term_if->else_instructions.get_tail())
return false;
} else {
if (term_if->then_instructions.get_head() ==
term_if->then_instructions.get_tail())
return false;
}
return true;
}
ir_visitor_status
loop_unroll_visitor::visit_leave(ir_loop *ir)
{
loop_variable_state *const ls = this->state->get(ir);
/* If we've entered a loop that hasn't been analyzed, something really,
* really bad has happened.
*/
if (ls == NULL) {
assert(ls != NULL);
return visit_continue;
}
/* Limiting terminator may have iteration count of zero,
* this is a valid case because the loop may break during
* the first iteration.
*/
/* Remove the conditional break statements associated with all terminators
* that are associated with a fixed iteration count, except for the one
* associated with the limiting terminator--that one needs to stay, since
* it terminates the loop. Exception: if the loop still has a normative
* bound, then that terminates the loop, so we don't even need the limiting
* terminator.
*/
foreach_in_list_safe(loop_terminator, t, &ls->terminators) {
if (t->iterations < 0)
continue;
exec_list *branch_instructions;
if (t != ls->limiting_terminator) {
ir_instruction *ir_if_last = (ir_instruction *)
t->ir->then_instructions.get_tail();
if (is_break(ir_if_last)) {
branch_instructions = &t->ir->else_instructions;
} else {
branch_instructions = &t->ir->then_instructions;
assert(is_break((ir_instruction *)
t->ir->else_instructions.get_tail()));
}
exec_list copy_list;
copy_list.make_empty();
clone_ir_list(ir, ©_list, branch_instructions);
t->ir->insert_before(©_list);
t->ir->remove();
assert(ls->num_loop_jumps > 0);
ls->num_loop_jumps--;
/* Also remove it from the terminator list */
t->remove();
this->progress = true;
}
}
if (ls->limiting_terminator == NULL) {
ir_instruction *last_ir =
(ir_instruction *) ir->body_instructions.get_tail();
/* If a loop has no induction variable and the last instruction is
* a break, unroll the loop with a count of 1. This is the classic
*
* do {
* // ...
* } while (false)
*
* that is used to wrap multi-line macros.
*
* If num_loop_jumps is not zero, last_ir cannot be NULL... there has to
* be at least num_loop_jumps instructions in the loop.
*/
if (ls->num_loop_jumps == 1 && is_break(last_ir)) {
last_ir->remove();
simple_unroll(ir, 1);
}
/* Don't try to unroll loops where the number of iterations is not known
* at compile-time.
*/
return visit_continue;
}
int iterations = ls->limiting_terminator->iterations;
const int max_iterations = options->MaxUnrollIterations;
/* Don't try to unroll loops that have zillions of iterations either.
*/
if (iterations > max_iterations)
return visit_continue;
/* Don't try to unroll nested loops and loops with a huge body.
*/
loop_unroll_count count(&ir->body_instructions, ls, options);
bool loop_too_large =
count.nested_loop || count.nodes * iterations > max_iterations * 5;
if (loop_too_large && !count.unsupported_variable_indexing &&
!count.array_indexed_by_induction_var_with_exact_iterations)
return visit_continue;
/* Note: the limiting terminator contributes 1 to ls->num_loop_jumps.
* We'll be removing the limiting terminator before we unroll.
*/
assert(ls->num_loop_jumps > 0);
unsigned predicted_num_loop_jumps = ls->num_loop_jumps - 1;
if (predicted_num_loop_jumps > 1)
return visit_continue;
if (predicted_num_loop_jumps == 0) {
simple_unroll(ir, iterations);
return visit_continue;
}
ir_instruction *last_ir = (ir_instruction *) ir->body_instructions.get_tail();
assert(last_ir != NULL);
if (is_break(last_ir)) {
/* If the only loop-jump is a break at the end of the loop, the loop
* will execute exactly once. Remove the break and use the simple
* unroller with an iteration count of 1.
*/
last_ir->remove();
simple_unroll(ir, 1);
return visit_continue;
}
/* Complex unrolling can only handle two terminators. One with an unknown
* iteration count and one with a known iteration count. We have already
* made sure we have a known iteration count above and removed any
* unreachable terminators with a known count. Here we make sure there
* isn't any additional unknown terminators, or any other jumps nested
* inside futher ifs.
*/
if (ls->num_loop_jumps != 2 || ls->terminators.length() != 2)
return visit_continue;
ir_instruction *first_ir =
(ir_instruction *) ir->body_instructions.get_head();
unsigned term_count = 0;
bool first_term_then_continue = false;
foreach_in_list(loop_terminator, t, &ls->terminators) {
ir_if *ir_if = t->ir->as_if();
assert(ir_if != NULL);
ir_instruction *ir_if_last =
(ir_instruction *) ir_if->then_instructions.get_tail();
if (is_break(ir_if_last)) {
splice_post_if_instructions(ir_if, &ir_if->else_instructions);
ir_if_last->remove();
if (term_count == 1) {
bool ebi =
exit_branch_has_instructions(ls->limiting_terminator->ir,
first_term_then_continue);
complex_unroll(ir, iterations, false,
first_ir->as_if() != ls->limiting_terminator->ir ||
ebi,
first_term_then_continue);
return visit_continue;
}
} else {
ir_if_last =
(ir_instruction *) ir_if->else_instructions.get_tail();
assert(is_break(ir_if_last));
if (is_break(ir_if_last)) {
splice_post_if_instructions(ir_if, &ir_if->then_instructions);
ir_if_last->remove();
if (term_count == 1) {
bool ebi =
exit_branch_has_instructions(ls->limiting_terminator->ir,
first_term_then_continue);
complex_unroll(ir, iterations, true,
first_ir->as_if() != ls->limiting_terminator->ir ||
ebi,
first_term_then_continue);
return visit_continue;
} else {
first_term_then_continue = true;
}
}
}
term_count++;
}
/* Did not find the break statement. It must be in a complex if-nesting,
* so don't try to unroll.
*/
return visit_continue;
}
bool
unroll_loops(exec_list *instructions, loop_state *ls,
const struct gl_shader_compiler_options *options)
{
loop_unroll_visitor v(ls, options);
v.run(instructions);
return v.progress;
}