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/*
* Copyright © 2010 Intel Corporation
*
* Permission is hereby granted, free of charge, to any person obtaining a
* constant of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, constant, 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 constantright 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 CONSTANTRIGHT 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.
*/
/**
* \file opt_constant_propagation.cpp
*
* Tracks assignments of constants to channels of variables, and
* usage of those constant channels with direct usage of the constants.
*
* This can lead to constant folding and algebraic optimizations in
* those later expressions, while causing no increase in instruction
* count (due to constants being generally free to load from a
* constant push buffer or as instruction immediate values) and
* possibly reducing register pressure.
*/
#include "ir.h"
#include "ir_visitor.h"
#include "ir_rvalue_visitor.h"
#include "ir_basic_block.h"
#include "ir_optimization.h"
#include "compiler/glsl_types.h"
#include "util/hash_table.h"
namespace {
class acp_entry : public exec_node
{
public:
/* override operator new from exec_node */
DECLARE_LINEAR_ZALLOC_CXX_OPERATORS(acp_entry)
acp_entry(ir_variable *var, unsigned write_mask, ir_constant *constant)
{
assert(var);
assert(constant);
this->var = var;
this->write_mask = write_mask;
this->constant = constant;
this->initial_values = write_mask;
}
acp_entry(const acp_entry *src)
{
this->var = src->var;
this->write_mask = src->write_mask;
this->constant = src->constant;
this->initial_values = src->initial_values;
}
ir_variable *var;
ir_constant *constant;
unsigned write_mask;
/** Mask of values initially available in the constant. */
unsigned initial_values;
};
class ir_constant_propagation_visitor : public ir_rvalue_visitor {
public:
ir_constant_propagation_visitor()
{
progress = false;
killed_all = false;
mem_ctx = ralloc_context(0);
this->lin_ctx = linear_alloc_parent(this->mem_ctx, 0);
this->acp = new(mem_ctx) exec_list;
this->kills = _mesa_pointer_hash_table_create(mem_ctx);
}
~ir_constant_propagation_visitor()
{
ralloc_free(mem_ctx);
}
virtual ir_visitor_status visit_enter(class ir_loop *);
virtual ir_visitor_status visit_enter(class ir_function_signature *);
virtual ir_visitor_status visit_enter(class ir_function *);
virtual ir_visitor_status visit_leave(class ir_assignment *);
virtual ir_visitor_status visit_enter(class ir_call *);
virtual ir_visitor_status visit_enter(class ir_if *);
void add_constant(ir_assignment *ir);
void constant_folding(ir_rvalue **rvalue);
void constant_propagation(ir_rvalue **rvalue);
void kill(ir_variable *ir, unsigned write_mask);
void handle_if_block(exec_list *instructions, hash_table *kills, bool *killed_all);
void handle_loop(class ir_loop *, bool keep_acp);
void handle_rvalue(ir_rvalue **rvalue);
/** List of acp_entry: The available constants to propagate */
exec_list *acp;
/**
* Hash table of killed entries: maps variables to the mask of killed channels.
*/
hash_table *kills;
bool progress;
bool killed_all;
void *mem_ctx;
void *lin_ctx;
};
void
ir_constant_propagation_visitor::constant_folding(ir_rvalue **rvalue)
{
if (this->in_assignee || *rvalue == NULL)
return;
if (ir_constant_fold(rvalue))
this->progress = true;
ir_dereference_variable *var_ref = (*rvalue)->as_dereference_variable();
if (var_ref && !var_ref->type->is_array()) {
ir_constant *constant =
var_ref->constant_expression_value(ralloc_parent(var_ref));
if (constant) {
*rvalue = constant;
this->progress = true;
}
}
}
void
ir_constant_propagation_visitor::constant_propagation(ir_rvalue **rvalue) {
if (this->in_assignee || !*rvalue)
return;
const glsl_type *type = (*rvalue)->type;
if (!type->is_scalar() && !type->is_vector())
return;
ir_swizzle *swiz = NULL;
ir_dereference_variable *deref = (*rvalue)->as_dereference_variable();
if (!deref) {
swiz = (*rvalue)->as_swizzle();
if (!swiz)
return;
deref = swiz->val->as_dereference_variable();
if (!deref)
return;
}
ir_constant_data data;
memset(&data, 0, sizeof(data));
for (unsigned int i = 0; i < type->components(); i++) {
int channel;
acp_entry *found = NULL;
if (swiz) {
switch (i) {
case 0: channel = swiz->mask.x; break;
case 1: channel = swiz->mask.y; break;
case 2: channel = swiz->mask.z; break;
case 3: channel = swiz->mask.w; break;
default: assert(!"shouldn't be reached"); channel = 0; break;
}
} else {
channel = i;
}
foreach_in_list(acp_entry, entry, this->acp) {
if (entry->var == deref->var && entry->write_mask & (1 << channel)) {
found = entry;
break;
}
}
if (!found)
return;
int rhs_channel = 0;
for (int j = 0; j < 4; j++) {
if (j == channel)
break;
if (found->initial_values & (1 << j))
rhs_channel++;
}
switch (type->base_type) {
case GLSL_TYPE_FLOAT:
data.f[i] = found->constant->value.f[rhs_channel];
break;
case GLSL_TYPE_FLOAT16:
data.f16[i] = found->constant->value.f16[rhs_channel];
break;
case GLSL_TYPE_DOUBLE:
data.d[i] = found->constant->value.d[rhs_channel];
break;
case GLSL_TYPE_INT:
data.i[i] = found->constant->value.i[rhs_channel];
break;
case GLSL_TYPE_UINT:
data.u[i] = found->constant->value.u[rhs_channel];
break;
case GLSL_TYPE_BOOL:
data.b[i] = found->constant->value.b[rhs_channel];
break;
case GLSL_TYPE_UINT64:
data.u64[i] = found->constant->value.u64[rhs_channel];
break;
case GLSL_TYPE_INT64:
data.i64[i] = found->constant->value.i64[rhs_channel];
break;
default:
assert(!"not reached");
break;
}
}
*rvalue = new(ralloc_parent(deref)) ir_constant(type, &data);
this->progress = true;
}
void
ir_constant_propagation_visitor::handle_rvalue(ir_rvalue **rvalue)
{
constant_propagation(rvalue);
constant_folding(rvalue);
}
ir_visitor_status
ir_constant_propagation_visitor::visit_enter(ir_function_signature *ir)
{
/* Treat entry into a function signature as a completely separate
* block. Any instructions at global scope will be shuffled into
* main() at link time, so they're irrelevant to us.
*/
exec_list *orig_acp = this->acp;
hash_table *orig_kills = this->kills;
bool orig_killed_all = this->killed_all;
this->acp = new(mem_ctx) exec_list;
this->kills = _mesa_pointer_hash_table_create(mem_ctx);
this->killed_all = false;
visit_list_elements(this, &ir->body);
this->kills = orig_kills;
this->acp = orig_acp;
this->killed_all = orig_killed_all;
return visit_continue_with_parent;
}
ir_visitor_status
ir_constant_propagation_visitor::visit_leave(ir_assignment *ir)
{
constant_folding(&ir->rhs);
if (this->in_assignee)
return visit_continue;
unsigned kill_mask = ir->write_mask;
if (ir->lhs->as_dereference_array()) {
/* The LHS of the assignment uses an array indexing operator (e.g. v[i]
* = ...;). Since we only try to constant propagate vectors and
* scalars, this means that either (a) array indexing is being used to
* select a vector component, or (b) the variable in question is neither
* a scalar or a vector, so we don't care about it. In the former case,
* we want to kill the whole vector, since in general we can't predict
* which vector component will be selected by array indexing. In the
* latter case, it doesn't matter what we do, so go ahead and kill the
* whole variable anyway.
*
* Note that if the array index is constant (e.g. v[2] = ...;), we could
* in principle be smarter, but we don't need to, because a future
* optimization pass will convert it to a simple assignment with the
* correct mask.
*/
kill_mask = ~0;
}
kill(ir->lhs->variable_referenced(), kill_mask);
add_constant(ir);
return visit_continue;
}
ir_visitor_status
ir_constant_propagation_visitor::visit_enter(ir_function *ir)
{
(void) ir;
return visit_continue;
}
ir_visitor_status
ir_constant_propagation_visitor::visit_enter(ir_call *ir)
{
/* Do constant propagation on call parameters, but skip any out params */
foreach_two_lists(formal_node, &ir->callee->parameters,
actual_node, &ir->actual_parameters) {
ir_variable *sig_param = (ir_variable *) formal_node;
ir_rvalue *param = (ir_rvalue *) actual_node;
if (sig_param->data.mode != ir_var_function_out
&& sig_param->data.mode != ir_var_function_inout) {
ir_rvalue *new_param = param;
handle_rvalue(&new_param);
if (new_param != param)
param->replace_with(new_param);
else
param->accept(this);
}
}
/* Since we're unlinked, we don't (necssarily) know the side effects of
* this call. So kill all copies.
*/
acp->make_empty();
this->killed_all = true;
return visit_continue_with_parent;
}
void
ir_constant_propagation_visitor::handle_if_block(exec_list *instructions, hash_table *kills, bool *killed_all)
{
exec_list *orig_acp = this->acp;
hash_table *orig_kills = this->kills;
bool orig_killed_all = this->killed_all;
this->acp = new(mem_ctx) exec_list;
this->kills = kills;
this->killed_all = false;
/* Populate the initial acp with a constant of the original */
foreach_in_list(acp_entry, a, orig_acp) {
this->acp->push_tail(new(this->lin_ctx) acp_entry(a));
}
visit_list_elements(this, instructions);
*killed_all = this->killed_all;
this->kills = orig_kills;
this->acp = orig_acp;
this->killed_all = orig_killed_all;
}
ir_visitor_status
ir_constant_propagation_visitor::visit_enter(ir_if *ir)
{
ir->condition->accept(this);
handle_rvalue(&ir->condition);
hash_table *new_kills = _mesa_pointer_hash_table_create(mem_ctx);
bool then_killed_all = false;
bool else_killed_all = false;
handle_if_block(&ir->then_instructions, new_kills, &then_killed_all);
handle_if_block(&ir->else_instructions, new_kills, &else_killed_all);
if (then_killed_all || else_killed_all) {
acp->make_empty();
killed_all = true;
} else {
hash_table_foreach(new_kills, htk)
kill((ir_variable *) htk->key, (uintptr_t) htk->data);
}
_mesa_hash_table_destroy(new_kills, NULL);
/* handle_if_block() already descended into the children. */
return visit_continue_with_parent;
}
void
ir_constant_propagation_visitor::handle_loop(ir_loop *ir, bool keep_acp)
{
exec_list *orig_acp = this->acp;
hash_table *orig_kills = this->kills;
bool orig_killed_all = this->killed_all;
this->acp = new(mem_ctx) exec_list;
this->kills = _mesa_pointer_hash_table_create(mem_ctx);
this->killed_all = false;
if (keep_acp) {
foreach_in_list(acp_entry, a, orig_acp) {
this->acp->push_tail(new(this->lin_ctx) acp_entry(a));
}
}
visit_list_elements(this, &ir->body_instructions);
if (this->killed_all) {
orig_acp->make_empty();
}
hash_table *new_kills = this->kills;
this->kills = orig_kills;
this->acp = orig_acp;
this->killed_all = this->killed_all || orig_killed_all;
hash_table_foreach(new_kills, htk) {
kill((ir_variable *) htk->key, (uintptr_t) htk->data);
}
}
ir_visitor_status
ir_constant_propagation_visitor::visit_enter(ir_loop *ir)
{
/* Make a conservative first pass over the loop with an empty ACP set.
* This also removes any killed entries from the original ACP set.
*/
handle_loop(ir, false);
/* Then, run it again with the real ACP set, minus any killed entries.
* This takes care of propagating values from before the loop into it.
*/
handle_loop(ir, true);
/* already descended into the children. */
return visit_continue_with_parent;
}
void
ir_constant_propagation_visitor::kill(ir_variable *var, unsigned write_mask)
{
assert(var != NULL);
/* We don't track non-vectors. */
if (!var->type->is_vector() && !var->type->is_scalar())
return;
/* Remove any entries currently in the ACP for this kill. */
foreach_in_list_safe(acp_entry, entry, this->acp) {
if (entry->var == var) {
entry->write_mask &= ~write_mask;
if (entry->write_mask == 0)
entry->remove();
}
}
/* Add this writemask of the variable to the hash table of killed
* variables in this block.
*/
hash_entry *kill_hash_entry = _mesa_hash_table_search(this->kills, var);
if (kill_hash_entry) {
uintptr_t new_write_mask = ((uintptr_t) kill_hash_entry->data) | write_mask;
kill_hash_entry->data = (void *) new_write_mask;
return;
}
/* Not already in the hash table. Make new entry. */
_mesa_hash_table_insert(this->kills, var, (void *) uintptr_t(write_mask));
}
/**
* Adds an entry to the available constant list if it's a plain assignment
* of a variable to a variable.
*/
void
ir_constant_propagation_visitor::add_constant(ir_assignment *ir)
{
acp_entry *entry;
if (ir->condition)
return;
if (!ir->write_mask)
return;
ir_dereference_variable *deref = ir->lhs->as_dereference_variable();
ir_constant *constant = ir->rhs->as_constant();
if (!deref || !constant)
return;
/* Only do constant propagation on vectors. Constant matrices,
* arrays, or structures would require more work elsewhere.
*/
if (!deref->var->type->is_vector() && !deref->var->type->is_scalar())
return;
/* We can't do copy propagation on buffer variables, since the underlying
* memory storage is shared across multiple threads we can't be sure that
* the variable value isn't modified between this assignment and the next
* instruction where its value is read.
*/
if (deref->var->data.mode == ir_var_shader_storage ||
deref->var->data.mode == ir_var_shader_shared)
return;
entry = new(this->lin_ctx) acp_entry(deref->var, ir->write_mask, constant);
this->acp->push_tail(entry);
}
} /* unnamed namespace */
/**
* Does a constant propagation pass on the code present in the instruction stream.
*/
bool
do_constant_propagation(exec_list *instructions)
{
ir_constant_propagation_visitor v;
visit_list_elements(&v, instructions);
return v.progress;
}