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[subgroups][non_uniform_broadcast] Fix broadcasting index generation #1680

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merged 6 commits into from
Mar 12, 2024
Merged

[subgroups][non_uniform_broadcast] Fix broadcasting index generation #1680

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9bbab53
[subgroups][non_uniform_broadcast] Fix broadcasting index generation
Nuullll Mar 23, 2023
082f5dd
Merge branch 'master' into fix-sub_group_non_uniform_broadcast
Nuullll Sep 27, 2023
2dcf4af
Revert "[subgroups][non_uniform_broadcast] Fix broadcasting index gen…
Nuullll Sep 27, 2023
cf67385
[subgroups][non_uniform_broadcast] Fix broadcasting index generation
Nuullll Sep 27, 2023
050239c
Merge branch 'main' into fix-sub_group_non_uniform_broadcast
Nuullll Feb 28, 2024
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Nuullll Feb 28, 2024
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9 changes: 8 additions & 1 deletion test_conformance/subgroups/subgroup_common_templates.h
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Original file line number Diff line number Diff line change
Expand Up @@ -82,14 +82,21 @@ template <typename Ty, SubgroupsBroadcastOp operation> struct BC
// broadcasted (one the same value for whole subgroup)
if (operation != SubgroupsBroadcastOp::broadcast)
{
// reduce brodcasting index in case of non_uniform and
// reduce broadcasting index in case of non_uniform and
// last workgroup last subgroup
if (last_subgroup_size && j == nj - 1
&& last_subgroup_size < NR_OF_ACTIVE_WORK_ITEMS)
{
bcast_if = bcast_index % last_subgroup_size;
bcast_elseif = bcast_if;
}
// reduce broadcasting index in case subgroup size <=
// NR_OF_ACTIVE_WORK_ITEMS (i.e. all items are active)
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This highlights a problem with the broadcast tests: they currently are not meant to test subgroup sizes <= NR_OF_ACTIVE_WORK_ITEMS (i.e., 4). Your proposed fix causes the test to skip an important aspect of non-uniform subgroup operations, as the else in sub_group_non_uniform_broadcast_source will not be executed. That means the subgroup operation will not be tested properly when the subgroup size is <= 4, so I don't think we should commit this.

Instead, we should probably try to get rid of NR_OF_ACTIVE_WORK_ITEMS and use work-item masks to introduce divergence in the broadcast tests (as done for e.g. sub_group_non_uniform_any).

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Thanks for reviewing. I agree. Will update the PR.

else if (n <= NR_OF_ACTIVE_WORK_ITEMS)
{
bcast_if = bcast_index % n;
bcast_elseif = bcast_if;
}
else
{
bcast_if = bcast_index % NR_OF_ACTIVE_WORK_ITEMS;
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