llvm dev - Aug 2021 - report a clang bug: SSE4.1 instruction problem

Hi,
  I was build SSE performance work on mac intel. But I found the performance of
my SSE4.1 version code using in xcode 12.4 is not as good as xcode 10.1, so I
checked the assembly of my code. The one _mm_mul_epi() instruction was
translated into three pmuludq, which is the SSE2 instruction, while this was
normal when compiling on xcode 10.1 and _mm_mul_epi() was translated into
pmuldq. So I checked the clang version, and I found this error occured when
clang version larger than 7.0.0.
  The simple case can be found: https://godbolt.org/z/Tf7qeocvz
  I probably think this is a clang compiler bug. And I hope to get some advice
on how to solve this issue.
  Thanks.
Best,
  Wade















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For reference, this example was also filed here:
https://llvm.org/PR51371


On Fri, Aug 6, 2021 at 4:51 AM wade via llvm-dev <llvm-dev at
lists.llvm.org>
wrote:
> Hi,
>   I was build SSE performance work on mac intel. But I found the
performance of my SSE4.1 version code using in xcode 12.4 is not as good as
xcode 10.1, so I checked the assembly of my code. The one _mm_mul_epi()
instruction was translated into three pmuludq, which is the SSE2 instruction,
while this was normal when compiling on xcode 10.1 and _mm_mul_epi() was
translated into pmuldq. So I checked the clang version, and I found this error
occured when clang version larger than 7.0.0.
>   The simple case can be found: https://godbolt.org/z/Tf7qeocvz
>   I probably think this is a clang compiler bug. And I hope to get some
advice on how to solve this issue.
>   Thanks.
> Best,
>   Wade
>
>
>
>
>
>
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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