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From: "gabravier at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/96271] New: Failure to optimize memcmp of
 doubles to avoid going through memory
Date: Tue, 21 Jul 2020 16:41:40 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 11.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96271

            Bug ID: 96271
           Summary: Failure to optimize memcmp of doubles to avoid going
                    through memory
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

bool f(double a, double b)
{
   return memcmp(&a, &b, sizeof(double)) =3D=3D 0;
}

With -O3, LLVM outputs this :

f(double, double):
  movq rax, xmm0
  movq rcx, xmm1
  cmp rax, rcx
  sete al
  ret

GCC outputs this:

f(double, double):
  movsd QWORD PTR [rsp-8], xmm0
  movsd QWORD PTR [rsp-16], xmm1
  mov rax, QWORD PTR [rsp-16]
  cmp QWORD PTR [rsp-8], rax
  sete al
  ret=