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nir_lower_returns: Optimize phis before beginning the pass

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This adds a little extra work, since now dominance is computed and
blocks that don't just have then-return or else-return are looked at.
However it means that nir_lower_returns can now keep phis up to date
by inserting undefs without causing some phis to become non-trivial.

This ends up obviating a couple of tests for lower_returns.

Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22913>
This commit is contained in:
Jesse Natalie
2023-05-08 17:45:49 -07:00
committed by Marge Bot
parent a1b27c364f
commit 5d238c0c2c
3 changed files with 8 additions and 215 deletions
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1
src/compiler/nir/meson.build
View File

@@ -416,7 +416,6 @@ if with_tests
'tests/loop_analyze_tests.cpp',
'tests/loop_unroll_tests.cpp',
'tests/lower_alu_width_tests.cpp',
'tests/lower_returns_tests.cpp',
'tests/mod_analysis_tests.cpp',
'tests/negative_equal_tests.cpp',
'tests/opt_if_tests.cpp',

13
src/compiler/nir/nir_lower_returns.c
View File

@@ -132,11 +132,11 @@ lower_returns_in_if(nir_if *if_stmt, struct lower_returns_state *state)
*/
/* nir_cf_extract will not extract phis at the start of the block. In
* this case we know that any phis will have to have a single
* predecessor, so we can just replace the phi with its single source.
* this case we know that any phis will have to have had a single
* predecessor, and should've been removed by the opt_remove_phis before
* beginning this pass.
*/
nir_block *succ_block = nir_after_cf_node(&if_stmt->cf_node).block;
nir_opt_remove_phis_block(succ_block);
assert(nir_block_first_instr(succ_block) == NULL ||
nir_block_first_instr(succ_block)->type != nir_instr_type_phi);
@@ -298,11 +298,14 @@ nir_lower_returns_impl(nir_function_impl *impl)
bool
nir_lower_returns(nir_shader *shader)
{
bool progress = false;
/* Before removing jumps and adding undef sources to otherwise single-source phis,
* go ahead and simplify those single-source phis.
*/
bool progress = nir_opt_remove_phis(shader);
nir_foreach_function(function, shader) {
if (function->impl)
progress = nir_lower_returns_impl(function->impl) || progress;
progress |= nir_lower_returns_impl(function->impl) || progress;
}
return progress;

209
src/compiler/nir/tests/lower_returns_tests.cpp
View File

@@ -1,209 +0,0 @@
/*
* Copyright © 2020 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.
*/
#include <gtest/gtest.h>
#include "nir.h"
#include "nir_builder.h"
class nir_opt_lower_returns_test : public ::testing::Test {
protected:
nir_opt_lower_returns_test();
~nir_opt_lower_returns_test();
nir_builder bld;
nir_ssa_def *in_def;
};
nir_opt_lower_returns_test::nir_opt_lower_returns_test()
{
glsl_type_singleton_init_or_ref();
static const nir_shader_compiler_options options = { };
bld = nir_builder_init_simple_shader(MESA_SHADER_VERTEX, &options, "lower returns test");
nir_variable *var = nir_variable_create(bld.shader, nir_var_shader_in, glsl_int_type(), "in");
in_def = nir_load_var(&bld, var);
}
nir_opt_lower_returns_test::~nir_opt_lower_returns_test()
{
ralloc_free(bld.shader);
glsl_type_singleton_decref();
}
nir_phi_instr *create_one_source_phi(nir_shader *shader, nir_block *pred,
nir_ssa_def *def)
{
nir_phi_instr *phi = nir_phi_instr_create(shader);
nir_phi_instr_add_src(phi, pred, nir_src_for_ssa(def));
nir_ssa_dest_init(&phi->instr, &phi->dest, def->num_components,
def->bit_size);
return phi;
}
TEST_F(nir_opt_lower_returns_test, phis_after_loop)
{
/* Test that after lowering of "return" the phis in block_5
* have two sources, because block_2 will have block_5
* as a successor.
*
* block block_0:
* loop {
* block block_1:
* if ssa_2 {
* block block_2:
* return
* // succs: block_6
* } else {
* block block_3:
* break;
* // succs: block_5
* }
* block block_4:
* }
* block block_5:
* // preds: block_3
* vec1 32 ssa_4 = phi block_3: ssa_1
* vec1 32 ssa_5 = phi block_3: ssa_1
* // succs: block_6
* block block_6:
*/
nir_loop *loop = nir_push_loop(&bld);
nir_ssa_def *one = nir_imm_int(&bld, 1);
nir_ssa_def *cmp_result = nir_ieq(&bld, in_def, one);
nir_if *nif = nir_push_if(&bld, cmp_result);
nir_jump(&bld, nir_jump_return);
nir_push_else(&bld, NULL);
nir_jump(&bld, nir_jump_break);
nir_pop_if(&bld, NULL);
nir_block *else_block = nir_if_last_else_block(nif);
nir_pop_loop(&bld, loop);
bld.cursor = nir_after_cf_node_and_phis(&loop->cf_node);
nir_phi_instr *const phi_1 =
create_one_source_phi(bld.shader, else_block, one);
nir_builder_instr_insert(&bld, &phi_1->instr);
nir_phi_instr *const phi_2 =
create_one_source_phi(bld.shader, else_block, one);
nir_builder_instr_insert(&bld, &phi_2->instr);
ASSERT_TRUE(nir_lower_returns(bld.shader));
EXPECT_EQ(phi_1->srcs.length(), 2);
EXPECT_EQ(phi_2->srcs.length(), 2);
nir_validate_shader(bld.shader, NULL);
}
TEST_F(nir_opt_lower_returns_test, phis_after_outer_loop)
{
/* Test that after lowering of "return" the phis in block_7
* have two sources, because block_6 will have a conditional break
* inserted, which will add a new predcessor to block_7.
*
* block block_0:
* loop {
* block block_1:
* loop {
* block block_2:
* if ssa_2 {
* block block_3:
* return
* // succs: block_8
* } else {
* block block_4:
* break;
* // succs: block_6
* }
* block block_5:
* }
* block block_6:
* break;
* // succs: block_7
* }
* block block_7:
* // preds: block_6
* vec1 32 ssa_4 = phi block_6: ssa_1
* vec1 32 ssa_5 = phi block_6: ssa_1
* // succs: block_8
* block block_8:
*/
nir_loop *loop_outer = nir_push_loop(&bld);
bld.cursor = nir_after_cf_list(&loop_outer->body);
nir_loop *loop_inner = nir_push_loop(&bld);
bld.cursor = nir_after_cf_list(&loop_inner->body);
nir_ssa_def *one = nir_imm_int(&bld, 1);
nir_ssa_def *cmp_result = nir_ieq(&bld, in_def, one);
nir_push_if(&bld, cmp_result);
nir_jump(&bld, nir_jump_return);
nir_push_else(&bld, NULL);
nir_jump(&bld, nir_jump_break);
nir_pop_if(&bld, NULL);
nir_pop_loop(&bld, loop_inner);
bld.cursor = nir_after_cf_node_and_phis(&loop_inner->cf_node);
nir_jump(&bld, nir_jump_break);
nir_pop_loop(&bld, loop_outer);
bld.cursor = nir_after_cf_node_and_phis(&loop_outer->cf_node);
nir_phi_instr *const phi_1 =
create_one_source_phi(bld.shader, nir_loop_last_block(loop_outer), one);
nir_builder_instr_insert(&bld, &phi_1->instr);
nir_phi_instr *const phi_2 =
create_one_source_phi(bld.shader, nir_loop_last_block(loop_outer), one);
nir_builder_instr_insert(&bld, &phi_2->instr);
ASSERT_TRUE(nir_lower_returns(bld.shader));
EXPECT_EQ(phi_1->srcs.length(), 2);
EXPECT_EQ(phi_2->srcs.length(), 2);
nir_validate_shader(bld.shader, NULL);
}