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/*
* 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.
*/
/**
* \file opt_constant_folding.cpp
* Replace constant-valued expressions with references to constant values.
*/
#include "ir.h"
#include "ir_visitor.h"
#include "ir_rvalue_visitor.h"
#include "ir_optimization.h"
#include "compiler/glsl_types.h"
namespace {
/**
* Visitor class for replacing expressions with ir_constant values.
*/
class ir_constant_folding_visitor : public ir_rvalue_visitor {
public:
ir_constant_folding_visitor()
{
this->progress = false;
}
virtual ~ir_constant_folding_visitor()
{
/* empty */
}
virtual ir_visitor_status visit_enter(ir_discard *ir);
virtual ir_visitor_status visit_enter(ir_assignment *ir);
virtual ir_visitor_status visit_enter(ir_call *ir);
virtual void handle_rvalue(ir_rvalue **rvalue);
bool progress;
};
} /* unnamed namespace */
bool
ir_constant_fold(ir_rvalue **rvalue)
{
if (*rvalue == NULL || (*rvalue)->ir_type == ir_type_constant)
return false;
/* Note that we do rvalue visitoring on leaving. So if an
* expression has a non-constant operand, no need to go looking
* down it to find if it's constant. This cuts the time of this
* pass down drastically.
*/
ir_expression *expr = (*rvalue)->as_expression();
if (expr) {
for (unsigned int i = 0; i < expr->num_operands; i++) {
if (!expr->operands[i]->as_constant())
return false;
}
}
/* Ditto for swizzles. */
ir_swizzle *swiz = (*rvalue)->as_swizzle();
if (swiz && !swiz->val->as_constant())
return false;
/* Ditto for array dereferences */
ir_dereference_array *array_ref = (*rvalue)->as_dereference_array();
if (array_ref && (!array_ref->array->as_constant() ||
!array_ref->array_index->as_constant()))
return false;
/* No constant folding can be performed on variable dereferences. We need
* to explicitly avoid them, as calling constant_expression_value() on a
* variable dereference will return a clone of var->constant_value. This
* would make us propagate the value into the tree, which isn't our job.
*/
ir_dereference_variable *var_ref = (*rvalue)->as_dereference_variable();
if (var_ref)
return false;
ir_constant *constant =
(*rvalue)->constant_expression_value(ralloc_parent(*rvalue));
if (constant) {
*rvalue = constant;
return true;
}
return false;
}
void
ir_constant_folding_visitor::handle_rvalue(ir_rvalue **rvalue)
{
if (ir_constant_fold(rvalue))
this->progress = true;
}
ir_visitor_status
ir_constant_folding_visitor::visit_enter(ir_discard *ir)
{
if (ir->condition) {
ir->condition->accept(this);
handle_rvalue(&ir->condition);
ir_constant *const_val = ir->condition->as_constant();
/* If the condition is constant, either remove the condition or
* remove the never-executed assignment.
*/
if (const_val) {
if (const_val->value.b[0])
ir->condition = NULL;
else
ir->remove();
this->progress = true;
}
}
return visit_continue_with_parent;
}
ir_visitor_status
ir_constant_folding_visitor::visit_enter(ir_assignment *ir)
{
ir->rhs->accept(this);
handle_rvalue(&ir->rhs);
if (ir->condition) {
ir->condition->accept(this);
handle_rvalue(&ir->condition);
ir_constant *const_val = ir->condition->as_constant();
/* If the condition is constant, either remove the condition or
* remove the never-executed assignment.
*/
if (const_val) {
if (const_val->value.b[0])
ir->condition = NULL;
else
ir->remove();
this->progress = true;
}
}
/* Don't descend into the LHS because we want it to stay as a
* variable dereference. FINISHME: We probably should to get array
* indices though.
*/
return visit_continue_with_parent;
}
ir_visitor_status
ir_constant_folding_visitor::visit_enter(ir_call *ir)
{
/* Attempt to constant fold parameters */
foreach_two_lists(formal_node, &ir->callee->parameters,
actual_node, &ir->actual_parameters) {
ir_rvalue *param_rval = (ir_rvalue *) actual_node;
ir_variable *sig_param = (ir_variable *) formal_node;
if (sig_param->data.mode == ir_var_function_in
|| sig_param->data.mode == ir_var_const_in) {
ir_rvalue *new_param = param_rval;
handle_rvalue(&new_param);
if (new_param != param_rval) {
param_rval->replace_with(new_param);
}
}
}
/* Next, see if the call can be replaced with an assignment of a constant */
ir_constant *const_val = ir->constant_expression_value(ralloc_parent(ir));
if (const_val != NULL) {
ir_assignment *assignment =
new(ralloc_parent(ir)) ir_assignment(ir->return_deref, const_val);
ir->replace_with(assignment);
}
return visit_continue_with_parent;
}
bool
do_constant_folding(exec_list *instructions)
{
ir_constant_folding_visitor constant_folding;
visit_list_elements(&constant_folding, instructions);
return constant_folding.progress;
}