[llvm-bugs] [Bug 51371] New: X86 SSE4.1 instruction problem

via llvm-bugs llvm-bugs at lists.llvm.org
Thu Aug 5 18:48:40 PDT 2021


            Bug ID: 51371
           Summary: X86 SSE4.1 instruction problem
           Product: clang
           Version: 7.0
          Hardware: PC
                OS: MacOS X
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C
          Assignee: unassignedclangbugs at nondot.org
          Reporter: oucwangshiwei at 163.com
                CC: blitzrakete at gmail.com, dgregor at apple.com,
                    erik.pilkington at gmail.com, llvm-bugs at lists.llvm.org,
                    richard-llvm at metafoo.co.uk

  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.

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