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broadcom/compiler: fix incorrect flags setup in non-uniform if path

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If the ELSE block is cheap then we don't emit the branch instruction
but we still want to generate the flags, since these are setting
the flags for the THEN block too.

Fixes: e401add741 ("broadcom/compiler: skip jumps in non-uniform if/then when block cost is small")
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27211>
(cherry picked from commit 29d4924e5e)
This commit is contained in:
Iago Toral Quiroga 2024-01-24 09:32:40 +01:00 • committed by Eric Engestrom
parent 438a064a9c
commit a085877c56
2 changed files with 11 additions and 3 deletions
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2
.pick_status.json
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@ -344,7 +344,7 @@
"description": "broadcom/compiler: fix incorrect flags setup in non-uniform if path",
"nominated": true,
"nomination_type": 1,
"resolution": 0,
"resolution": 1,
"main_sha": null,
"because_sha": "e401add741f33d113fe1496298e35ad00ce6a878",
"notes": null

12
src/broadcom/compiler/nir_to_vir.c
View file

@ -3957,19 +3957,27 @@ ntq_emit_nonuniform_if(struct v3d_compile *c, nir_if *if_stmt)
c->execute,
vir_uniform_ui(c, else_block->index));
/* Set the flags for taking the THEN block */
vir_set_pf(c, vir_MOV_dest(c, vir_nop_reg(), c->execute),
V3D_QPU_PF_PUSHZ);
/* Jump to ELSE if nothing is active for THEN (unless THEN block is
* so small it won't pay off), otherwise fall through.
*/
bool is_cheap = exec_list_is_singular(&if_stmt->then_list) &&
is_cheap_block(nir_if_first_then_block(if_stmt));
if (!is_cheap) {
vir_set_pf(c, vir_MOV_dest(c, vir_nop_reg(), c->execute), V3D_QPU_PF_PUSHZ);
vir_BRANCH(c, V3D_QPU_BRANCH_COND_ALLNA);
vir_link_blocks(c->cur_block, else_block);
}
vir_link_blocks(c->cur_block, then_block);
/* Process the THEN block. */
/* Process the THEN block.
*
* Notice we don't call ntq_activate_execute_for_block here on purpose:
* c->execute is already set up to be 0 for lanes that must take the
* THEN block.
*/
vir_set_emit_block(c, then_block);
ntq_emit_cf_list(c, &if_stmt->then_list);