/*
* 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 flattens if-statements to conditional assignments if:
*
* - the GPU has limited or no flow control support
* (controlled by max_depth)
*
* - small conditional branches are more expensive than conditional assignments
* (controlled by min_branch_cost, that's the cost for a branch to be
* preserved)
*
* 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 "compiler/glsl_types.h"
#include "ir.h"
#include "util/set.h"
#include "util/hash_table.h" /* Needed for the hashing functions */
#include "main/macros.h" /* for MAX2 */
namespace {
class ir_if_to_cond_assign_visitor : public ir_hierarchical_visitor {
public:
ir_if_to_cond_assign_visitor(gl_shader_stage stage,
unsigned max_depth,
unsigned min_branch_cost)
{
this->progress = false;
this->stage = stage;
this->max_depth = max_depth;
this->min_branch_cost = min_branch_cost;
this->depth = 0;
this->condition_variables =
_mesa_set_create(NULL, _mesa_hash_pointer,
_mesa_key_pointer_equal);
}
~ir_if_to_cond_assign_visitor()
{
_mesa_set_destroy(this->condition_variables, NULL);
}
ir_visitor_status visit_enter(ir_if *);
ir_visitor_status visit_leave(ir_if *);
bool found_unsupported_op;
bool found_expensive_op;
bool found_dynamic_arrayref;
bool is_then;
bool progress;
gl_shader_stage stage;
unsigned then_cost;
unsigned else_cost;
unsigned min_branch_cost;
unsigned max_depth;
unsigned depth;
struct set *condition_variables;
};
} /* anonymous namespace */
bool
lower_if_to_cond_assign(gl_shader_stage stage, exec_list *instructions,
unsigned max_depth, unsigned min_branch_cost)
{
if (max_depth == UINT_MAX)
return false;
ir_if_to_cond_assign_visitor v(stage, max_depth, min_branch_cost);
visit_list_elements(&v, instructions);
return v.progress;
}
static void
check_ir_node(ir_instruction *ir, void *data)
{
ir_if_to_cond_assign_visitor *v = (ir_if_to_cond_assign_visitor *)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:
case ir_type_emit_vertex:
case ir_type_end_primitive:
case ir_type_barrier:
v->found_unsupported_op = true;
break;
case ir_type_dereference_variable: {
ir_variable *var = ir->as_dereference_variable()->variable_referenced();
/* Lowering branches with TCS output accesses breaks many piglit tests,
* so don't touch them for now.
*/
if (v->stage == MESA_SHADER_TESS_CTRL &&
var->data.mode == ir_var_shader_out)
v->found_unsupported_op = true;
break;
}
/* SSBO, images, atomic counters are handled by ir_type_call */
case ir_type_texture:
v->found_expensive_op = true;
break;
case ir_type_dereference_array: {
ir_dereference_array *deref = ir->as_dereference_array();
if (deref->array_index->ir_type != ir_type_constant)
v->found_dynamic_arrayref = true;
} /* fall-through */
case ir_type_expression:
case ir_type_dereference_record:
if (v->is_then)
v->then_cost++;
else
v->else_cost++;
break;
default:
break;
}
}
static void
move_block_to_cond_assign(void *mem_ctx,
ir_if *if_ir, ir_rvalue *cond_expr,
exec_list *instructions,
struct set *set)
{
foreach_in_list_safe(ir_instruction, ir, instructions) {
if (ir->ir_type == ir_type_assignment) {
ir_assignment *assign = (ir_assignment *)ir;
if (_mesa_set_search(set, assign) == NULL) {
_mesa_set_add(set, 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 =
_mesa_set_search(
set, 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 *)
{
this->depth++;
return visit_continue;
}
ir_visitor_status
ir_if_to_cond_assign_visitor::visit_leave(ir_if *ir)
{
bool must_lower = this->depth-- > this->max_depth;
/* Only flatten when beyond the GPU's maximum supported nesting depth. */
if (!must_lower && this->min_branch_cost == 0)
return visit_continue;
this->found_unsupported_op = false;
this->found_expensive_op = false;
this->found_dynamic_arrayref = false;
this->then_cost = 0;
this->else_cost = 0;
ir_assignment *assign;
/* Check that both blocks don't contain anything we can't support. */
this->is_then = true;
foreach_in_list(ir_instruction, then_ir, &ir->then_instructions) {
visit_tree(then_ir, check_ir_node, this);
}
this->is_then = false;
foreach_in_list(ir_instruction, else_ir, &ir->else_instructions) {
visit_tree(else_ir, check_ir_node, this);
}
if (this->found_unsupported_op)
return visit_continue; /* can't handle inner unsupported opcodes */
/* Skip if the branch cost is high enough or if there's an expensive op.
*
* Also skip if non-constant array indices were encountered, since those
* can be out-of-bounds for a not-taken branch, and so generating an
* assignment would be incorrect. In the case of must_lower, it's up to the
* backend to deal with any potential fall-out (perhaps by translating the
* assignments to hardware-predicated moves).
*/
if (!must_lower &&
(this->found_expensive_op ||
this->found_dynamic_arrayref ||
MAX2(this->then_cost, this->else_cost) >= this->min_branch_cost))
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.
*/
_mesa_set_add(this->condition_variables, 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.
*/
_mesa_set_add(this->condition_variables, else_var);
}
ir->remove();
this->progress = true;
return visit_continue;
}