[PATCH] D101297: [SLP]Allow masked gathers only if allowed by target.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev added a comment.

In D101297#2719505 <https://reviews.llvm.org/D101297#2719505>, @spatel wrote:

> In D101297#2719479 <https://reviews.llvm.org/D101297#2719479>, @ABataev wrote:
>
>> In D101297#2719468 <https://reviews.llvm.org/D101297#2719468>, @spatel wrote:
>>
>>> We seem to go back and forth on legality vs. pure cost model to decide what is allowed for vectorization.
>>> This would undo part of D90445 <https://reviews.llvm.org/D90445>, so adding potential reviewers for more feedback.
>>
>> Pure cost won't work here, we need to check if this is legal just to try to generate masked gather at all. Cost problem is different.
>
> Is there some gather construct that is impossible for the backend to expand correctly or just that it can't be expanded efficiently?

There is known problem that after landing of the patch with masked gathers some of the code produces wrong results, so I suppose yes, there is a problem with lowering. Generally speaking, would be good to calculate the cost/lower masked gathers to simple gathers if it is not legal/not profitable to use masked gathers. And tweak the cost model for such a case. AS temp solution we can add simple legality checks, at least, without early checks for the cost.


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https://reviews.llvm.org/D101297