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From: "gabravier at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/94866] New: Failure to optimize pinsrq of 0 with index 1
 into movq
Date: Thu, 30 Apr 2020 00:21:37 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94866

            Bug ID: 94866
           Summary: Failure to optimize pinsrq of 0 with index 1 into movq
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

typedef int64_t v2di __attribute__((vector_size(16)));
typedef int32_t v2si __attribute__((vector_size(8)));

v2di _mm_move_epi64(v2di a)
{
    return v2di{a[0], 0LL};
}

LLVM with `-O3 -msse4.1` compiles this to this :=20

_mm_move_epi64(long __vector(2)): # @_mm_move_epi64(long __vector(2))
  movq xmm0, xmm0 # xmm0 =3D xmm0[0],zero
  ret

GCC gives :

_mm_move_epi64(long __vector(2)):
  xor eax, eax
  pinsrq xmm0, rax, 1
  ret

GCC's output seems like it would naturally be much slower, so unless there =
is
something seriously messed up with x86 chips that I've missed, LLVM's versi=
on
should be faster=