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brw/dce: Don't generate more NULL destinations after brw_lower_3src_null_dest

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Later commits will call DCE after lowering has been performed. Creating
more things that would need lowering is problematic.

No shader-db or fossil-db changes on any Intel platform.

Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38315>
This commit is contained in:
Ian Romanick 2025-02-25 09:06:40 -08:00
parent 24cd8aa3b8
commit 50f2cd7366
1 changed files with 10 additions and 2 deletions
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12
src/intel/compiler/brw/brw_opt_dead_code_eliminate.cpp
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@ -51,12 +51,18 @@ can_eliminate(const intel_device_info *devinfo, const brw_inst *inst,
* Is it safe to omit the write, making the destination ARF null?
*/
static bool
can_omit_write(const brw_inst *inst)
can_omit_write(const brw_compiler *compiler, const brw_inst *inst, bool late)
{
switch (inst->opcode) {
case SHADER_OPCODE_MEMORY_ATOMIC_LOGICAL:
return true;
default:
/* Dead code elimination that occurs once after brw_lower_3src_null_dest
* should not generate more NULL destinations.
*/
if (inst->is_3src(compiler) && late)
return false;
/* We can eliminate the destination write for ordinary instructions,
* but not most SENDs.
*/
@ -100,6 +106,7 @@ bool
brw_opt_dead_code_eliminate(brw_shader &s)
{
const intel_device_info *devinfo = s.devinfo;
const bool late = s.phase >= BRW_SHADER_PHASE_AFTER_LATE_LOWERING;
bool progress = false;
@ -123,7 +130,8 @@ brw_opt_dead_code_eliminate(brw_shader &s)
result_live |= BITSET_TEST(live, var + i);
if (!result_live &&
(can_omit_write(inst) || can_eliminate(devinfo, inst, flag_live))) {
(can_omit_write(s.compiler, inst, late) ||
can_eliminate(devinfo, inst, flag_live))) {
inst->dst = brw_reg(spread(retype(brw_null_reg(), inst->dst.type),
inst->dst.stride));
progress = true;