/*
* 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 lower_if_to_cond_assign.cpp
*
* This attempts to flatten if-statements to conditional assignments for
* GPUs with limited or no flow control support.
*
* It can't handle other control flow being inside of its block, such
* as calls or loops. Hopefully loop unrolling and inlining will take
* care of those.
*
* Drivers for GPUs with no control flow support should simply call
*
* lower_if_to_cond_assign(instructions)
*
* to attempt to flatten all if-statements.
*
* Some GPUs (such as i965 prior to gen6) do support control flow, but have a
* maximum nesting depth N. Drivers for such hardware can call
*
* lower_if_to_cond_assign(instructions, N)
*
* to attempt to flatten any if-statements appearing at depth > N.
*/
#include "glsl_types.h"
#include "ir.h"
#include "program/hash_table.h"
class ir_if_to_cond_assign_visitor : public ir_hierarchical_visitor {
public:
ir_if_to_cond_assign_visitor(unsigned max_depth)
{
this->progress = false;
this->max_depth = max_depth;
this->depth = 0;
this->condition_variables = hash_table_ctor(0, hash_table_pointer_hash,
hash_table_pointer_compare);
}
~ir_if_to_cond_assign_visitor()
{
hash_table_dtor(this->condition_variables);
}
ir_visitor_status visit_enter(ir_if *);
ir_visitor_status visit_leave(ir_if *);
bool progress;
unsigned max_depth;
unsigned depth;
struct hash_table *condition_variables;
};
bool
lower_if_to_cond_assign(exec_list *instructions, unsigned max_depth)
{
if (max_depth == UINT_MAX)
return false;
ir_if_to_cond_assign_visitor v(max_depth);
visit_list_elements(&v, instructions);
return v.progress;
}
void
check_control_flow(ir_instruction *ir, void *data)
{
bool *found_control_flow = (bool *)data;
switch (ir->ir_type) {
case ir_type_call:
case ir_type_discard:
case ir_type_loop:
case ir_type_loop_jump:
case ir_type_return:
*found_control_flow = true;
break;
default:
break;
}
}
void
move_block_to_cond_assign(void *mem_ctx,
ir_if *if_ir, ir_rvalue *cond_expr,
exec_list *instructions,
struct hash_table *ht)
{
foreach_list_safe(node, instructions) {
ir_instruction *ir = (ir_instruction *) node;
if (ir->ir_type == ir_type_assignment) {
ir_assignment *assign = (ir_assignment *)ir;
if (hash_table_find(ht, assign) == NULL) {
hash_table_insert(ht, assign, assign);
/* If the LHS of the assignment is a condition variable that was
* previously added, insert an additional assignment of false to
* the variable.
*/
const bool assign_to_cv =
hash_table_find(ht, assign->lhs->variable_referenced()) != NULL;
if (!assign->condition) {
if (assign_to_cv) {
assign->rhs =
new(mem_ctx) ir_expression(ir_binop_logic_and,
glsl_type::bool_type,
cond_expr->clone(mem_ctx, NULL),
assign->rhs);
} else {
assign->condition = cond_expr->clone(mem_ctx, NULL);
}
} else {
assign->condition =
new(mem_ctx) ir_expression(ir_binop_logic_and,
glsl_type::bool_type,
cond_expr->clone(mem_ctx, NULL),
assign->condition);
}
}
}
/* Now, move from the if block to the block surrounding it. */
ir->remove();
if_ir->insert_before(ir);
}
}
ir_visitor_status
ir_if_to_cond_assign_visitor::visit_enter(ir_if *ir)
{
(void) ir;
this->depth++;
return visit_continue;
}
ir_visitor_status
ir_if_to_cond_assign_visitor::visit_leave(ir_if *ir)
{
/* Only flatten when beyond the GPU's maximum supported nesting depth. */
if (this->depth-- <= this->max_depth)
return visit_continue;
bool found_control_flow = false;
ir_assignment *assign;
/* Check that both blocks don't contain anything we can't support. */
foreach_iter(exec_list_iterator, then_iter, ir->then_instructions) {
ir_instruction *then_ir = (ir_instruction *)then_iter.get();
visit_tree(then_ir, check_control_flow, &found_control_flow);
}
foreach_iter(exec_list_iterator, else_iter, ir->else_instructions) {
ir_instruction *else_ir = (ir_instruction *)else_iter.get();
visit_tree(else_ir, check_control_flow, &found_control_flow);
}
if (found_control_flow)
return visit_continue;
void *mem_ctx = ralloc_parent(ir);
/* Store the condition to a variable. Move all of the instructions from
* the then-clause of the if-statement. Use the condition variable as a
* condition for all assignments.
*/
ir_variable *const then_var =
new(mem_ctx) ir_variable(glsl_type::bool_type,
"if_to_cond_assign_then",
ir_var_temporary);
ir->insert_before(then_var);
ir_dereference_variable *then_cond =
new(mem_ctx) ir_dereference_variable(then_var);
assign = new(mem_ctx) ir_assignment(then_cond, ir->condition);
ir->insert_before(assign);
move_block_to_cond_assign(mem_ctx, ir, then_cond,
&ir->then_instructions,
this->condition_variables);
/* Add the new condition variable to the hash table. This allows us to
* find this variable when lowering other (enclosing) if-statements.
*/
hash_table_insert(this->condition_variables, then_var, then_var);
/* If there are instructions in the else-clause, store the inverse of the
* condition to a variable. Move all of the instructions from the
* else-clause if the if-statement. Use the (inverse) condition variable
* as a condition for all assignments.
*/
if (!ir->else_instructions.is_empty()) {
ir_variable *const else_var =
new(mem_ctx) ir_variable(glsl_type::bool_type,
"if_to_cond_assign_else",
ir_var_temporary);
ir->insert_before(else_var);
ir_dereference_variable *else_cond =
new(mem_ctx) ir_dereference_variable(else_var);
ir_rvalue *inverse =
new(mem_ctx) ir_expression(ir_unop_logic_not,
then_cond->clone(mem_ctx, NULL));
assign = new(mem_ctx) ir_assignment(else_cond, inverse);
ir->insert_before(assign);
move_block_to_cond_assign(mem_ctx, ir, else_cond,
&ir->else_instructions,
this->condition_variables);
/* Add the new condition variable to the hash table. This allows us to
* find this variable when lowering other (enclosing) if-statements.
*/
hash_table_insert(this->condition_variables, else_var, else_var);
}
ir->remove();
this->progress = true;
return visit_continue;
}