/*
* 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_dead_code_local.cpp
*
* Eliminates local dead assignments from the code.
*
* This operates on basic blocks, tracking assignments and finding if
* they're used before the variable is completely reassigned.
*
* Compare this to ir_dead_code.cpp, which operates globally looking
* for assignments to variables that are never read.
*/
#include "ir.h"
#include "ir_basic_block.h"
#include "ir_optimization.h"
#include "glsl_types.h"
static bool debug = false;
class assignment_entry : public exec_node
{
public:
assignment_entry(ir_variable *lhs, ir_instruction *ir)
{
assert(lhs);
assert(ir);
this->lhs = lhs;
this->ir = ir;
}
ir_variable *lhs;
ir_instruction *ir;
};
class kill_for_derefs_visitor : public ir_hierarchical_visitor {
public:
kill_for_derefs_visitor(exec_list *assignments)
{
this->assignments = assignments;
}
virtual ir_visitor_status visit(ir_dereference_variable *ir)
{
ir_variable *const var = ir->variable_referenced();
foreach_iter(exec_list_iterator, iter, *this->assignments) {
assignment_entry *entry = (assignment_entry *)iter.get();
if (entry->lhs == var) {
if (debug)
printf("kill %s\n", entry->lhs->name);
entry->remove();
}
}
return visit_continue;
}
private:
exec_list *assignments;
};
class array_index_visit : public ir_hierarchical_visitor {
public:
array_index_visit(ir_hierarchical_visitor *v)
{
this->visitor = v;
}
virtual ir_visitor_status visit_enter(class ir_dereference_array *ir)
{
ir->array_index->accept(visitor);
return visit_continue;
}
static void run(ir_instruction *ir, ir_hierarchical_visitor *v)
{
array_index_visit top_visit(v);
ir->accept(& top_visit);
}
ir_hierarchical_visitor *visitor;
};
/**
* Adds an entry to the available copy list if it's a plain assignment
* of a variable to a variable.
*/
static bool
process_assignment(void *ctx, ir_assignment *ir, exec_list *assignments)
{
ir_variable *var = NULL;
bool progress = false;
kill_for_derefs_visitor v(assignments);
/* Kill assignment entries for things used to produce this assignment. */
ir->rhs->accept(&v);
if (ir->condition) {
ir->condition->accept(&v);
}
/* Kill assignment enties used as array indices.
*/
array_index_visit::run(ir->lhs, &v);
var = ir->lhs->variable_referenced();
assert(var);
bool always_assign = true;
if (ir->condition) {
ir_constant *condition = ir->condition->as_constant();
if (!condition || !condition->value.b[0])
always_assign = false;
}
/* Now, check if we did a whole-variable assignment. */
if (always_assign && (ir->whole_variable_written() != NULL)) {
/* We did a whole-variable assignment. So, any instruction in
* the assignment list with the same LHS is dead.
*/
if (debug)
printf("looking for %s to remove\n", var->name);
foreach_iter(exec_list_iterator, iter, *assignments) {
assignment_entry *entry = (assignment_entry *)iter.get();
if (entry->lhs == var) {
if (debug)
printf("removing %s\n", var->name);
entry->ir->remove();
entry->remove();
progress = true;
}
}
}
/* Add this instruction to the assignment list available to be removed.
* But not if the assignment has other side effects.
*/
if (ir_has_call(ir))
return progress;
assignment_entry *entry = new(ctx) assignment_entry(var, ir);
assignments->push_tail(entry);
if (debug) {
printf("add %s\n", var->name);
printf("current entries\n");
foreach_iter(exec_list_iterator, iter, *assignments) {
assignment_entry *entry = (assignment_entry *)iter.get();
printf(" %s\n", entry->lhs->name);
}
}
return progress;
}
static void
dead_code_local_basic_block(ir_instruction *first,
ir_instruction *last,
void *data)
{
ir_instruction *ir, *ir_next;
/* List of avaialble_copy */
exec_list assignments;
bool *out_progress = (bool *)data;
bool progress = false;
void *ctx = ralloc_context(NULL);
/* Safe looping, since process_assignment */
for (ir = first, ir_next = (ir_instruction *)first->next;;
ir = ir_next, ir_next = (ir_instruction *)ir->next) {
ir_assignment *ir_assign = ir->as_assignment();
if (debug) {
ir->print();
printf("\n");
}
if (ir_assign) {
progress = process_assignment(ctx, ir_assign, &assignments) || progress;
} else {
kill_for_derefs_visitor kill(&assignments);
ir->accept(&kill);
}
if (ir == last)
break;
}
*out_progress = progress;
ralloc_free(ctx);
}
/**
* Does a copy propagation pass on the code present in the instruction stream.
*/
bool
do_dead_code_local(exec_list *instructions)
{
bool progress = false;
call_for_basic_blocks(instructions, dead_code_local_basic_block, &progress);
return progress;
}