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brw: Set nir->info.{min,max}_subgroup_size in brw_nir_apply_key

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This records the actual SIMD width we selected for the shader, in
all cases except fragment shaders, where we don't know it yet.

MR 37258 notes that "Backends can update [these fields] when they make
new decisions about the subgroup size" - which is what we now do.

Note that nir->info.api_subgroup_size may be different than min/max
subgroup size on Vulkan prior to SPV1.6/VK_EXT_subgroup_size_control,
so we do not alter that.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40843>
This commit is contained in:
Kenneth Graunke 2026-04-06 17:25:32 -07:00 • committed by Marge Bot
parent d7d2d7aceb
commit 765d74eebe
1 changed files with 16 additions and 0 deletions
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16
src/intel/compiler/brw/brw_nir.c
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@ -3038,6 +3038,22 @@ brw_nir_apply_key(brw_pass_tracker *pt,
pt->progress = false;
unsigned subgroup_size = get_subgroup_size(&nir->info, max_subgroup_size);
/* VS/TCS/TES/GS always run at a fixed SIMD width, which is what our
* max_subgroup_size parameter represents. Compute/Mesh can run at
* different sizes, but we clone the NIR for each SIMD width, and pass
* our chosen width here as max_subgroup_size.
*
* For fragment shaders, we may dispatch at multiple SIMD widths,
* and use a single copy of the NIR for all sizes, so we can't lower
* the actual width at this point.
*/
if (nir->info.stage != MESA_SHADER_FRAGMENT) {
nir->info.min_subgroup_size = max_subgroup_size;
nir->info.max_subgroup_size = max_subgroup_size;
}
const nir_lower_subgroups_options subgroups_options = {
.subgroup_size = get_subgroup_size(&nir->info, max_subgroup_size),
.ballot_bit_size = 32,