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From: "nok.raven at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/96166] New: [10/11 Regression]
 -O3/-ftree-slp-vectorize turns ROL into a mess
Date: Sat, 11 Jul 2020 16:01:41 +0000
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X-Bugzilla-Component: tree-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96166

            Bug ID: 96166
           Summary: [10/11 Regression] -O3/-ftree-slp-vectorize turns ROL
                    into a mess
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nok.raven at gmail dot com
  Target Milestone: ---

inline void swap(int &x, int &y)
{
  int tmp =3D x;
  x =3D y;
  y =3D tmp;
}

void bar(int (&x)[2])
{
  int y[2];
  __builtin_memcpy(&y, &x, sizeof x);
  swap(y[0], y[1]);
  __builtin_memcpy(&x, &y, sizeof x);
}


GCC 9 (-Os/O2/O3) produces:
  rolq $32, (%rdi)

GCC 10/trunk (-O3/-ftree-slp-vectorize) produces:
  movq (%rdi), %rax
  movd (%rdi), %xmm1
  sarq $32, %rax
  movq %rax, %xmm0
  punpckldq %xmm1, %xmm0
  movq %xmm0, (%rdi)


https://godbolt.org/z/5h3bW8=