[PATCH] D98714: [SLP] Add insertelement instructions to vectorizable tree

[Douglas Yung via Phabricator via llvm-commits]

dyung added a comment.

Hi, this change has caused a regression in the codegen for one of our internal tests. Consider the following code:

  __attribute__((noinline))
  __m256d add_pd_002(__m256d a, __m256d b) {
    __m256d r = (__m256d){ a[0] + a[1], a[2] + a[3], b[0] + b[1], b[2] + b[3] };
    return __builtin_shufflevector(r, a, 0, -1, 2, 3);
  }

If you compile this with "-g0 -O3 -march=btver2", prior to your commit the compiler would generate the following code for the function:

  # %bb.0:                                # %entry
          vinsertf128     $1, %xmm1, %ymm0, %ymm0
          vhaddpd %ymm1, %ymm0, %ymm0

But after your change it is now generating the following code:

  # %bb.0:                                # %entry
          vextractf128    $1, %ymm1, %xmm2
          vhaddpd %xmm0, %xmm0, %xmm0
          vhaddpd %xmm2, %xmm1, %xmm1
          vperm2f128      $2, %ymm0, %ymm1, %ymm0 # ymm0 = ymm0[0,1],ymm1[0,1]

>From your commit description, it sounds like this is expected and will be fixed in a follow-up commit. Is my understanding of this correct?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D98714/new/

https://reviews.llvm.org/D98714