[llvm-bugs] [Bug 42633] New: [X86] Avoid scalar/vector transfers for scalar arithmetic

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42633

            Bug ID: 42633
           Summary: [X86] Avoid scalar/vector transfers for scalar
                    arithmetic
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, spatel+llvm at rotateright.com

https://godbolt.org/z/LvQiCP

#include <x86intrin.h>

auto add(__v4si x) {
    return _mm_set1_epi32(x[1] + x[3]);
}

_Z3addDv4_i:
  vextractps $1, %xmm0, %eax
  vextractps $3, %xmm0, %ecx
  addl %eax, %ecx
  vmovd %ecx, %xmm0
  vpshufd $0, %xmm0, %xmm0 # xmm0 = xmm0[0,0,0,0]
  retq


A more optimal method would be something like:

add(int __vector(4)):
  vpshufd xmm1, xmm0, 78          # xmm1 = xmm0[2,3,0,1]
  vpaddd  xmm0, xmm1, xmm0
  vpshufd xmm0, xmm0, 85          # xmm0 = xmm0[1,1,1,1]
  ret

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