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nir/opt_cse: update potential future plans merging copy propagation with CSE
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This matches my current understanding of nir_opt_copy_prop, including that
nir_opt_copy_prop always replaces movs with vecN.

Acked-by: Alyssa Rosenzweig <alyssa.rosenzweig@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38916>
This commit is contained in:
Marek Olšák 2025-12-11 16:33:54 -05:00 • committed by Marge Bot
parent 9ac8e643d6
commit d17d1f53bd
1 changed files with 9 additions and 8 deletions
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17
src/compiler/nir/nir_opt_cse.c
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@ -52,18 +52,19 @@
*
* Case 1. Copy propagation of movs without swizzles:
* 32x4 %2 = (any instruction)
* 32x4 %3 = mov %2.xyzw // eliminated since it's equal to %2
* 32x4 %3 = mov %2.xyzw // eliminated since it's equal to %2
* OR
* 32x4 %3 = vec4 %2.x, %2.y, %2.z, %2.w // eliminated since it's equal to %2
*
* Case 2. Copy propagation of movs with swizzles:
* 32x2 %2 = (any instruction)
* 32x3 %3 = mov %2.yxx // eliminated conditionally
* 32x3 %3 = mov %2.yxx // eliminated conditionally
* OR
* 32x3 %3 = vec3 %2.y, %2.x, %2.x // eliminated conditionally
* All %3 uses that are ALU will absorb the swizzle and are changed
* to use %2, and those uses that are not ALU will keep the mov.
*
* While vecN is possible to occur here instead, NIR should always create
* swizzled mov instead of vecN when all components use the same def, and
* nir_validate should assert that, so this should never occur:
* 32x4 %2 = vec4 %1.?, %1.?, %1.?, %1.?
* to use %2, and those uses that are not ALU will keep vecN or replace
* mov with equivalent vecN while eliminating components not used by
* the remaining uses (nir_opt_copy_prop always does that).
*/
#include "nir.h"