diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/compiler/Makefile.sources | 1 | ||||
| -rw-r--r-- | src/compiler/nir/nir.h | 2 | ||||
| -rw-r--r-- | src/compiler/nir/nir_opt_move_comparisons.c | 185 |
3 files changed, 188 insertions, 0 deletions
diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources index 7479afae047..063cf50be5b 100644 --- a/src/compiler/Makefile.sources +++ b/src/compiler/Makefile.sources @@ -246,6 +246,7 @@ NIR_FILES = \ nir/nir_opt_global_to_local.c \ nir/nir_opt_if.c \ nir/nir_opt_loop_unroll.c \ + nir/nir_opt_move_comparisons.c \ nir/nir_opt_peephole_select.c \ nir/nir_opt_remove_phis.c \ nir/nir_opt_trivial_continues.c \ diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h index 66cb36526bf..8bbc41d326e 100644 --- a/src/compiler/nir/nir.h +++ b/src/compiler/nir/nir.h @@ -2590,6 +2590,8 @@ bool nir_opt_if(nir_shader *shader); bool nir_opt_loop_unroll(nir_shader *shader, nir_variable_mode indirect_mask); +bool nir_opt_move_comparisons(nir_shader *shader); + bool nir_opt_peephole_select(nir_shader *shader, unsigned limit); bool nir_opt_remove_phis(nir_shader *shader); diff --git a/src/compiler/nir/nir_opt_move_comparisons.c b/src/compiler/nir/nir_opt_move_comparisons.c new file mode 100644 index 00000000000..617c2ca9989 --- /dev/null +++ b/src/compiler/nir/nir_opt_move_comparisons.c @@ -0,0 +1,185 @@ +/* + * Copyright © 2016 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 "nir.h" + +/** + * \file nir_opt_move_comparisons.c + * + * This pass moves ALU comparison operations just before their first use. + * + * It only moves instructions within a single basic block; cross-block + * movement is left to global code motion. + * + * Many GPUs generate condition codes for comparisons, and use predication + * for conditional selects and control flow. In a sequence such as: + * + * vec1 32 ssa_1 = flt a b + * <some other operations> + * vec1 32 ssa_2 = bcsel ssa_1 c d + * + * the backend would likely do the comparison, producing condition codes, + * then save those to a boolean value. The intervening operations might + * trash the condition codes. Then, in order to do the bcsel, it would + * need to re-populate the condition code register based on the boolean. + * + * By moving the comparison just before the bcsel, the condition codes could + * be used directly. This eliminates the need to reload them from the boolean + * (generally eliminating an instruction). It may also eliminate the need to + * create a boolean value altogether (unless it's used elsewhere), which could + * lower register pressure. + */ + +static bool +is_comparison(nir_op op) +{ + switch (op) { + case nir_op_flt: + case nir_op_fge: + case nir_op_feq: + case nir_op_fne: + case nir_op_ilt: + case nir_op_ult: + case nir_op_ige: + case nir_op_uge: + case nir_op_ieq: + case nir_op_ine: + case nir_op_i2b: + case nir_op_f2b: + case nir_op_inot: + case nir_op_fnot: + return true; + default: + return false; + } +} + +static bool +move_comparison_source(nir_src *src, nir_block *block, nir_instr *before) +{ + if (!src->is_ssa) + return false; + + nir_instr *src_instr = src->ssa->parent_instr; + + if (src_instr->block == block && + src_instr->type == nir_instr_type_alu && + is_comparison(nir_instr_as_alu(src_instr)->op)) { + + exec_node_remove(&src_instr->node); + + if (before) + exec_node_insert_node_before(&before->node, &src_instr->node); + else + exec_list_push_tail(&block->instr_list, &src_instr->node); + + return true; + } + + return false; +} + +static bool +move_comparison_source_cb(nir_src *src, void *data) +{ + bool *progress = data; + + nir_instr *instr = src->parent_instr; + if (move_comparison_source(src, instr->block, instr)) + *progress = true; + + return true; /* nir_foreach_src should keep going */ +} + +static bool +move_comparisons(nir_block *block) +{ + bool progress = false; + + /* We use a simple approach: walk instructions backwards. + * + * If the instruction's source is a comparison from the same block, + * simply move it here. This may break SSA if it's used earlier in + * the block as well. However, as we walk backwards, we'll find the + * earlier use and move it again, further up. It eventually ends up + * dominating all uses again, restoring SSA form. + * + * Before walking instructions, we consider the if-condition at the + * end of the block, if one exists. It's effectively a use at the + * bottom of the block. + */ + nir_if *iff = nir_block_get_following_if(block); + if (iff) { + progress |= move_comparison_source(&iff->condition, block, NULL); + } + + nir_foreach_instr_reverse(instr, block) { + /* The sources of phi instructions happen after the predecessor block + * but before this block. (Yes, that's between blocks). This means + * that we don't need to move them in order for them to be correct. + * We could move them to encourage comparisons that are used in a phi to + * the end of the block, doing so correctly would make the pass + * substantially more complicated and wouldn't gain us anything since + * the phi can't use a flag value anyway. + */ + if (instr->type == nir_instr_type_phi) { + /* We're going backwards so everything else is a phi too */ + break; + } else if (instr->type == nir_instr_type_alu) { + /* Walk ALU instruction sources backwards so that bcsel's boolean + * condition is processed last. + */ + nir_alu_instr *alu = nir_instr_as_alu(instr); + for (int i = nir_op_infos[alu->op].num_inputs - 1; i >= 0; i--) { + progress |= move_comparison_source(&alu->src[i].src, + block, instr); + } + } else { + nir_foreach_src(instr, move_comparison_source_cb, &progress); + } + } + + return progress; +} + +bool +nir_opt_move_comparisons(nir_shader *shader) +{ + bool progress = false; + + nir_foreach_function(func, shader) { + if (!func->impl) + continue; + + nir_foreach_block(block, func->impl) { + if (move_comparisons(block)) { + nir_metadata_preserve(func->impl, nir_metadata_block_index | + nir_metadata_dominance | + nir_metadata_live_ssa_defs); + progress = true; + } + } + } + + return progress; +} |