[PATCH] D111220: [X86][LV][TTI][Costmodel] LoopVectorizer: don't use `TTI::isLegalMaskedGather()` hook, introduce `TTI::shouldUseMaskedGatherForVectorization()`

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

In D111220#3048397 <https://reviews.llvm.org/D111220#3048397>, @RKSimon wrote:

> How good is the gather/scatter scalarization at splitting vectorized geps? Doing pointer math on the vector unit (probably using a single splatted base pointer) and then having to extract every pointer is going to be pretty poor compared to scalarizing and using LEA op on x86.

Hmm it's not: https://godbolt.org/z/eYzP4ob3G
I guess we might want to:

1. teach vectorcombine to split vector geps iff all their uses are extracts
2. schedule additional run of vectorcombine after the scalarizer

But that doesn't affect cost model though, i believe.


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