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From: "glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/25290] PHI-OPT could be rewritten so that is uses fold
Date: Sun, 19 May 2013 09:43:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25290

Marc Glisse <glisse at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |glisse at gcc dot gnu.org

--- Comment #6 from Marc Glisse <glisse at gcc dot gnu.org> ---
I assume it would help with this?

int f(int a,int b){
  return (a<0)&(b<0);
}
int g(int a,int b){
  return (a<0)?(b<0):0;
}
int h(int a,int b){
  if (a<0) return (b<0);
  return 0;
}

where (on x86) we turn g into f, but we don't notice that h is the same. In
asm, that is:

    movl    %esi, %eax
    andl    %edi, %eax
    shrl    $31, %eax

((a<0)&(b<0) is later optimized to (a&b)<0)

vs

    shrl    $31, %esi
    xorl    %eax, %eax
    testl    %edi, %edi
    cmovs    %esi, %eax