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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_discard_simplification.cpp
*
* This pass simplifies if-statements and loops containing unconditional
* discards.
*
* Case 1: Both branches contain unconditional discards:
* -----------------------------------------------------
*
* if (cond) {
* s1;
* discard;
* s2;
* } else {
* s3;
* discard;
* s4;
* }
*
* becomes:
*
* discard
*
* Case 2: The "then" clause contains an unconditional discard:
* ------------------------------------------------------------
*
* if (cond) {
* s1;
* discard;
* s2;
* } else {
* s3;
* }
*
* becomes:
*
* if (cond) {
* discard;
* } else {
* s3;
* }
*
* Case 3: The "else" clause contains an unconditional discard:
* ------------------------------------------------------------
*
* if (cond) {
* s1;
* } else {
* s2;
* discard;
* s3;
* }
*
* becomes:
*
* if (cond) {
* s1;
* } else {
* discard;
* }
*/
#include "glsl_types.h"
#include "ir.h"
class discard_simplifier : public ir_hierarchical_visitor {
public:
discard_simplifier()
{
this->progress = false;
}
ir_visitor_status visit_enter(ir_if *);
ir_visitor_status visit_enter(ir_loop *);
ir_visitor_status visit_enter(ir_assignment *);
bool progress;
};
static ir_discard *
find_unconditional_discard(exec_list &instructions)
{
foreach_list(n, &instructions) {
ir_instruction *ir = (ir_instruction *)n;
if (ir->ir_type == ir_type_return ||
ir->ir_type == ir_type_loop_jump)
return NULL;
/* So far, this code doesn't know how to look inside of flow
* control to see if a discard later on at this level is
* unconditional.
*/
if (ir->ir_type == ir_type_if ||
ir->ir_type == ir_type_loop)
return NULL;
ir_discard *discard = ir->as_discard();
if (discard != NULL && discard->condition == NULL)
return discard;
}
return NULL;
}
static bool
is_only_instruction(ir_discard *discard)
{
return (discard->prev->is_head_sentinel() &&
discard->next->is_tail_sentinel());
}
/* We only care about the top level instructions, so don't descend
* into expressions.
*/
ir_visitor_status
discard_simplifier::visit_enter(ir_assignment *ir)
{
return visit_continue_with_parent;
}
ir_visitor_status
discard_simplifier::visit_enter(ir_if *ir)
{
ir_discard *then_discard = find_unconditional_discard(ir->then_instructions);
ir_discard *else_discard = find_unconditional_discard(ir->else_instructions);
if (then_discard == NULL && else_discard == NULL)
return visit_continue;
/* If both branches result in discard, replace whole if with discard. */
if (then_discard != NULL && else_discard != NULL) {
this->progress = true;
ir->replace_with(then_discard);
return visit_continue_with_parent;
}
/* Otherwise, one branch has a discard. */
if (then_discard != NULL && !is_only_instruction(then_discard)) {
this->progress = true;
ir->then_instructions.make_empty();
ir->then_instructions.push_tail(then_discard);
} else if (else_discard != NULL && !is_only_instruction(else_discard)) {
this->progress = true;
ir->else_instructions.make_empty();
ir->else_instructions.push_tail(else_discard);
}
visit_list_elements(this, &ir->then_instructions);
return visit_continue_with_parent;
}
ir_visitor_status
discard_simplifier::visit_enter(ir_loop *ir)
{
ir_discard *discard = find_unconditional_discard(ir->body_instructions);
if (discard) {
ir->replace_with(discard);
return visit_continue_with_parent;
}
return visit_continue;
}
bool
do_discard_simplification(exec_list *instructions)
{
/* Look for a top-level unconditional discard */
ir_discard *discard = find_unconditional_discard(*instructions);
if (discard != NULL) {
instructions->make_empty();
instructions->push_tail(discard);
return true;
}
discard_simplifier v;
visit_list_elements(&v, instructions);
return v.progress;
}
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