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

[Alexey Bataev via Phabricator via llvm-commits]

ABataev added a comment.

In D101297#2735948 <https://reviews.llvm.org/D101297#2735948>, @uabelho wrote:

> In D101297#2735939 <https://reviews.llvm.org/D101297#2735939>, @ABataev wrote:
>
>> In D101297#2735772 <https://reviews.llvm.org/D101297#2735772>, @uabelho wrote:
>>
>>> In D101297#2735721 <https://reviews.llvm.org/D101297#2735721>, @uabelho wrote:
>>>
>>>> I'm seeing a strange case with this patch where I now get calls to
>>>>
>>>>   llvm.masked.gather.v2i16.v2p0i16
>>>>
>>>> after SLP vectorizer and before we didn't?
>>>> Masked gather is not legal on my target. Something seems to be backwards?
>>>
>>> In my case the cost as computed by TTI->getGatherScatterOpCost (so the cost prior to this patch) is 6 but calculated in the new way (since masked gather is not legal) I get the cost 0. getGatherCost(VL) returns 2 and then getEntryCost(It->get()) 2 as well so VecLdCost now ends up as 0.
>>
>> If the masked gather is not legal, it should be converted to a regular gather by `scalarizeMaskedGather` function (called by `ScalarizeMaskedMemIntrinLegacyPass::runOnFunction`), that's why we calculate it as a regular gather
>
> So you say it is expected that with this patch, for a target where masked gather is not legal, the SLP Vectorizer should now suddenly introduce @llvm.masked.gather where it didn't before?

Well, generally speaking, yes. Just if it is not legal, it should be scalarized and turned into a regular gather later. And the patch calculates the cost of the gather, if it is not legal


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