[PATCH] D100486: [COST]Improve cost model for shuffles in SLP.

Thu May 5 14:46:21 PDT 2022

asbirlea added a comment.

In D100486#3494746 <https://reviews.llvm.org/D100486#3494746>, @ABataev wrote:

> In D100486#3494581 <https://reviews.llvm.org/D100486#3494581>, @asbirlea wrote:
>
>> We currently root-caused a 20% regression in eigen complex to this patch and it is blocking our compiler release.
>> I need some time to do additional testing, given there are at least a few patches on top of this. So far I see a crash fix, two NFCs and two additional changes that may also affect performance (https://reviews.llvm.org/D114171 and https://reviews.llvm.org/D115750).
>> Can you please hold off on any additional changes while we test further, or include them here for review so I can check if they resolve the regressions seen so far?
>
> Most probably, some overoptimistic cost model estimations turned on some extra vectorization. The reproducer will help, if you can provide it.

The reproducer is open source: https://gitlab.com/libeigen/eigen
Regressions are on haswell platform, xfdo configuration; the compiler used is bootstrapped against itself; revision tested includes this patch and all follow-up changes to the SLPVectorizer including D114171 <https://reviews.llvm.org/D114171> and excluding D115750 <https://reviews.llvm.org/D115750>.
A few number samples:
BM_MatrixVectorMultiply_Complex_EigenRowMajorDynamic_float_16x64_ 16%
BM_MatrixVectorMultiply_Complex_EigenRowMajorDynamic_float_64x64_ 17%
BM_MatrixVectorMultiply_Complex_EigenRowMajorFixed_float_64x64_ 15%
BM_MatrixVectorMultiply_Complex_EigenRowMajorFixed_float_16x64_ 14%

Repository:
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https://reviews.llvm.org/D100486