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spirv: Run repair_ssa if there are discard instructions

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SPIR-V's OpKill is a control-flow instruction but NIR's discard is not.
Therefore, it can be valid SPIR-V to have

    if (...) {
        foo = /* something */
    } else {
        discard;
    }
    use(foo);

without any phi between the definition of foo and its use.  This is not
true in NIR, however, because NIR's discard isn't considered
control-flow.  Arguably, this is a NIR bug but making discard control-
flow is a very deep change that can have serious ans subtle
side-effects.   The easier thing to do is just fix up the SSA in case we
have an OpKill which might have gotten us into the above case.

Fixes dEQP-VK.graphicsfuzz.vectors-and-discard-in-function with the new
NIR dominance validation pass enabled.

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5288>
(cherry picked from commit 7cedc4128a)
This commit is contained in:
Jason Ekstrand 2020-06-01 18:01:05 -05:00 • committed by Dylan Baker
parent b617a52308
commit 66a14f9c41
3 changed files with 4 additions and 2 deletions
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2
.pick_status.json
View file

@ -1048,7 +1048,7 @@
"description": "spirv: Run repair_ssa if there are discard instructions",
"nominated": true,
"nomination_type": 0,
"resolution": 0,
"resolution": 1,
"master_sha": null,
"because_sha": null
},

3
src/compiler/spirv/vtn_cfg.c
View file

@ -616,6 +616,7 @@ vtn_process_block(struct vtn_builder *b,
return NULL;
case SpvOpKill:
b->has_kill = true;
block->branch_type = vtn_branch_type_discard;
return NULL;
@ -1185,7 +1186,7 @@ vtn_function_emit(struct vtn_builder *b, struct vtn_function *func,
* but instructions in the continue may use SSA defs in the loop body.
* Therefore, we need to repair SSA to insert the needed phi nodes.
*/
if (b->has_loop_continue)
if (b->has_loop_continue || b->has_kill)
nir_repair_ssa_impl(func->impl);
func->emitted = true;

1
src/compiler/spirv/vtn_private.h
View file

@ -679,6 +679,7 @@ struct vtn_builder {
unsigned func_param_idx;
bool has_loop_continue;
bool has_kill;
/* false by default, set to true by the ContractionOff execution mode */
bool exact;