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spirv: Don't emit RMW for vector indexing in shared or global

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Anything that fails the is_external_block check is getting the
vtn_local_load/store path which does read-modify-write which isn't
correct if the variable mode can be written cross-workgroup.

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6372>
(cherry picked from commit b479de8537)
This commit is contained in:
Jason Ekstrand 2020-08-17 10:51:32 -05:00 • committed by Eric Engestrom
parent 1b470ee09f
commit ffc0433259
2 changed files with 18 additions and 6 deletions
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2
.pick_status.json
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@ -706,7 +706,7 @@
"description": "spirv: Don't emit RMW for vector indexing in shared or global",
"nominated": true,
"nomination_type": 0,
"resolution": 0,
"resolution": 1,
"master_sha": null,
"because_sha": null
},

22
src/compiler/spirv/vtn_variables.c
View file

@ -131,6 +131,18 @@ vtn_mode_uses_ssa_offset(struct vtn_builder *b,
mode == vtn_variable_mode_push_constant;
}
static bool
vtn_mode_is_cross_invocation(struct vtn_builder *b,
enum vtn_variable_mode mode)
{
return mode == vtn_variable_mode_ssbo ||
mode == vtn_variable_mode_ubo ||
mode == vtn_variable_mode_phys_ssbo ||
mode == vtn_variable_mode_push_constant ||
mode == vtn_variable_mode_workgroup ||
mode == vtn_variable_mode_cross_workgroup;
}
static bool
vtn_pointer_is_external_block(struct vtn_builder *b,
struct vtn_pointer *ptr)
@ -1093,11 +1105,11 @@ _vtn_variable_load_store(struct vtn_builder *b, bool load,
if (glsl_type_is_vector_or_scalar(ptr->type->type)) {
/* We hit a vector or scalar; go ahead and emit the load[s] */
nir_deref_instr *deref = vtn_pointer_to_deref(b, ptr);
if (vtn_pointer_is_external_block(b, ptr)) {
/* If it's external, we call nir_load/store_deref directly. The
* vtn_local_load/store helpers are too clever and do magic to
* avoid array derefs of vectors. That magic is both less
* efficient than the direct load/store and, in the case of
if (vtn_mode_is_cross_invocation(b, ptr->mode)) {
/* If it's cross-invocation, we call nir_load/store_deref
* directly. The vtn_local_load/store helpers are too clever and
* do magic to avoid array derefs of vectors. That magic is both
* less efficient than the direct load/store and, in the case of
* stores, is broken because it creates a race condition if two
* threads are writing to different components of the same vector
* due to the load+insert+store it uses to emulate the array