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[X86][SSE] Failure to merge 2 x float stores to <2 x float> store #41237

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RKSimon opened this issue May 15, 2019 · 1 comment
Open

[X86][SSE] Failure to merge 2 x float stores to <2 x float> store #41237

RKSimon opened this issue May 15, 2019 · 1 comment
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backend:X86 bugzilla Issues migrated from bugzilla

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@RKSimon
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RKSimon commented May 15, 2019 •
edited

Bugzilla Link 41892
Version trunk
OS Windows NT
CC @anton-afanasyev,@topperc,@RKSimon,@rotateright

Extended Description

https://godbolt.org/z/InfZZK

#include <x86intrin.h>

void sum_pairs_128(__m128 f, float *p) {
  p[0] = f[0] + f[1];
  p[1] = f[2] + f[3];
}

clang -O3 -march=btver2

_Z13sum_pairs_128Dv4_fPf: # @_Z13sum_pairs_128Dv4_fPf
  vhaddps %xmm0, %xmm0, %xmm0
  vmovss %xmm0, (%rdi)
  vextractps $1, %xmm0, 4(%rdi)
  retq

would be better if we managed to merge to:

_Z13sum_pairs_128Dv4_fPf: # @_Z13sum_pairs_128Dv4_fPf
  vhaddps %xmm0, %xmm0, %xmm0
  vmovsd %xmm0, (%rdi)
  retq
@RKSimon
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RKSimon commented May 17, 2019 •
edited

float3 cases would be useful as well: https://godbolt.org/z/DRs8Qf

#include <x86intrin.h>

void store_float3(__m128 f, float *p) {
  *p++ = f[0];
  *p++ = f[1];
  *p++ = f[2];
}

void store_float3_splat(__m128 f, float *p) {
  *p++ = f[0];
  *p++ = f[0];
  *p++ = f[0];
}

_Z12store_float3Dv4_fPf: # @_Z12store_float3Dv4_fPf
  vmovss %xmm0, (%rdi)
  vextractps $1, %xmm0, 4(%rdi)
  vextractps $2, %xmm0, 8(%rdi)
  retq
_Z18store_float3_splatDv4_fPf: # @_Z18store_float3_splatDv4_fPf
  vmovss %xmm0, (%rdi)
  vmovss %xmm0, 4(%rdi)
  vmovss %xmm0, 8(%rdi)
  retq

which could be:

_Z12store_float3Dv4_fPf: # @_Z12store_float3Dv4_fPf
  vmovsd %xmm0, (%rdi)
  vextractps $2, %xmm0, 8(%rdi)
  retq
_Z18store_float3_splatDv4_fPf: # @_Z18store_float3_splatDv4_fPf
  vpermilps $0, %xmm0, %xmm0 # xmm0 = xmm0[0,0,0,0]
  vmovsd %xmm0, (%rdi)
  movss xmm0, 8(%rdi)
  retq

@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 10, 2021
RKSimon added a commit that referenced this issue May 8, 2022
@RKSimon
[SLP][X86] Add test coverage for PR41892 / Issue #41237
7d94597
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