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brw/cmod: Don't propagate from CMP to ADD if there is a write between

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If either source of the CMP is modified before an appropriate ADD is
found, the ADD and the CMP will not have the same result.

shader-db:

Lunar Lake
total instructions in shared programs: 17098815 -> 17098818 (<.01%)
instructions in affected programs: 1187 -> 1190 (0.25%)
helped: 0 / HURT: 3

total cycles in shared programs: 876858960 -> 876858968 (<.01%)
cycles in affected programs: 6878 -> 6886 (0.12%)
helped: 0 / HURT: 1

Meteor Lake, DG2, Tiger Lake, Ice Lake, and Skylake had similar results. (Meteor Lake shown)
total instructions in shared programs: 20034973 -> 20034984 (<.01%)
instructions in affected programs: 4599 -> 4610 (0.24%)
helped: 0 / HURT: 11

total cycles in shared programs: 881033088 -> 881033108 (<.01%)
cycles in affected programs: 57872 -> 57892 (0.03%)
helped: 0 / HURT: 5

fossil-db:

All Intel platforms had similar results. (Lunar Lake shown)
Totals:
Instrs: 918873064 -> 918873269 (+0.00%)
CodeSize: 14747338416 -> 14747339360 (+0.00%); split: -0.00%, +0.00%
Cycle count: 104141836677 -> 104141840371 (+0.00%); split: -0.00%, +0.00%

Totals from 205 (0.01% of 2011421) affected shaders:
Instrs: 290415 -> 290620 (+0.07%)
CodeSize: 4280704 -> 4281648 (+0.02%); split: -0.01%, +0.03%
Cycle count: 18166526 -> 18170220 (+0.02%); split: -0.00%, +0.02%

Closes: #14874
Fixes: 020b0055e7 ("i965/fs: Propagate conditional modifiers from compares to adds")
Reviewed-by: Matt Turner <mattst88@gmail.com>
Tested-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/39967>
This commit is contained in:
Ian Romanick 2026-02-17 11:38:22 -08:00 • committed by Marge Bot
parent 6ebb502ab9
commit d1614cd6db
2 changed files with 32 additions and 0 deletions
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11
src/intel/compiler/brw/brw_opt_cmod_propagation.cpp
View file

@ -99,6 +99,17 @@ cmod_propagate_cmp_to_add(const intel_device_info *devinfo, brw_inst *inst)
}
foreach_inst_in_block_reverse_starting_from(brw_inst, scan_inst, inst) {
/* If either of the sources of the CMP is modified, the optimization
* cannot occur. This is the case even if the instruction modifying the
* value is an ADD of the appropriate form.
*/
if (regions_overlap(scan_inst->dst, scan_inst->size_written,
inst->src[0], inst->size_read(devinfo, 0)) ||
regions_overlap(scan_inst->dst, scan_inst->size_written,
inst->src[1], inst->size_read(devinfo, 1))) {
break;
}
if (scan_inst->opcode == BRW_OPCODE_ADD &&
!scan_inst->predicate &&
scan_inst->dst.is_contiguous() &&

21
src/intel/compiler/brw/test_opt_cmod_propagation.cpp
View file

@ -693,6 +693,27 @@ TEST_F(cmod_propagation_test, subtract_delete_compare)
EXPECT_SHADERS_MATCH(bld, exp);
}
TEST_F(cmod_propagation_test, subtract_no_delete_compare_write_between)
{
brw_builder bld = make_shader();
brw_reg dest = vgrf(bld, BRW_TYPE_F);
brw_reg src0 = vgrf(bld, BRW_TYPE_F);
set_condmod(BRW_CONDITIONAL_L, bld.ADD(dest, src0, brw_imm_f(-1.0f)));
bld.MOV(src0, brw_imm_f(5.0));
bld.CMP(bld.null_reg_f(), src0, brw_imm_f(1.0f), BRW_CONDITIONAL_L);
/* = Before =
* 0: add.l.f0(8) dest0:F src0:F -1.0:F
* 1: mov(0) src0:F 5.0:F
* 2: cmp.l.f0(8) null:F src0:F 1.0:F
*
* = After =
* No changes.
*/
EXPECT_NO_PROGRESS(brw_opt_cmod_propagation, bld);
}
TEST_F(cmod_propagation_test, subtract_delete_compare_other_flag)
{
/* This test is the same as subtract_delete_compare but it explicitly used