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nir/lower_indirect_derefs: don't lower compact arrays unconditionally to fix perf

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This fixes bad mesh shader performance. See the comment.

Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38155>
This commit is contained in:
Marek Olšák 2025-10-29 23:31:44 -04:00 • committed by Marge Bot
parent cb6cb2697e
commit 86dd74aaeb
1 changed files with 24 additions and 6 deletions
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30
src/compiler/nir/nir_lower_indirect_derefs.c
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@ -155,12 +155,30 @@ lower_indirect_derefs_block(nir_block *block, nir_builder *b,
if (glsl_type_is_cmat(base->type))
continue;
/* Only lower variables whose mode is in the mask, or compact
* array variables. (We can't handle indirects on tightly packed
* scalar arrays, so we need to lower them regardless.)
*/
if (!(modes & base->var->data.mode) && !base->var->data.compact)
continue;
if (base->var->data.compact) {
/* Originally, this pass ignored "modes" if the array was compact,
* which reduced mesh shader performance for RADV by double digits
* due to lowering indirect gl_ClipDistance[64][4] into a gigantic
* if-else ladder with 256 output stores. This adds minimum checking
* to fix that.
*
* Skip lowering compact arrays for inputs and outputs according
* to NIR options.
*/
mesa_shader_stage stage_bit = BITFIELD_BIT(b->shader->info.stage);
nir_variable_mode supported_modes = 0;
if (b->shader->options->support_indirect_inputs & stage_bit)
supported_modes |= nir_var_shader_in;
if (b->shader->options->support_indirect_outputs & stage_bit)
supported_modes |= nir_var_shader_out;
if (supported_modes & base->var->data.mode)
continue;
} else {
if (!(modes & base->var->data.mode))
continue;
}
if (vars && !_mesa_set_search(vars, base->var))
continue;