/*
* 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"
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;
}
ir_visitor_status visit_enter(ir_if *);
ir_visitor_status visit_leave(ir_if *);
bool progress;
unsigned max_depth;
unsigned depth;
};
bool
lower_if_to_cond_assign(exec_list *instructions, unsigned max_depth)
{
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_variable *cond_var, bool then)
{
exec_list *instructions;
if (then) {
instructions = &if_ir->then_instructions;
} else {
instructions = &if_ir->else_instructions;
}
foreach_iter(exec_list_iterator, iter, *instructions) {
ir_instruction *ir = (ir_instruction *)iter.get();
if (ir->ir_type == ir_type_assignment) {
ir_assignment *assign = (ir_assignment *)ir;
ir_rvalue *cond_expr;
ir_dereference *deref = new(mem_ctx) ir_dereference_variable(cond_var);
if (then) {
cond_expr = deref;
} else {
cond_expr = new(mem_ctx) ir_expression(ir_unop_logic_not,
glsl_type::bool_type,
deref,
NULL);
}
if (!assign->condition) {
assign->condition = cond_expr;
} else {
assign->condition = new(mem_ctx) ir_expression(ir_binop_logic_and,
glsl_type::bool_type,
cond_expr,
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;
this->depth--;
bool found_control_flow = false;
ir_variable *cond_var;
ir_assignment *assign;
ir_dereference_variable *deref;
/* 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 so the assignment conditions are
* simpler.
*/
cond_var = new(mem_ctx) ir_variable(glsl_type::bool_type,
"if_to_cond_assign_condition",
ir_var_temporary);
ir->insert_before(cond_var);
deref = new(mem_ctx) ir_dereference_variable(cond_var);
assign = new(mem_ctx) ir_assignment(deref,
ir->condition, NULL);
ir->insert_before(assign);
/* Now, move all of the instructions out of the if blocks, putting
* conditions on assignments.
*/
move_block_to_cond_assign(mem_ctx, ir, cond_var, true);
move_block_to_cond_assign(mem_ctx, ir, cond_var, false);
ir->remove();
this->progress = true;
return visit_continue;
}