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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/96572] New: Failure to optimize out branch
 when it always results in UB from dereferencing a pointer to an undefined
 value set in there
Date: Tue, 11 Aug 2020 17:07:06 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 11.0
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: gabravier at gmail dot com
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96572

            Bug ID: 96572
           Summary: Failure to optimize out branch when it always results
                    in UB from dereferencing a pointer to an undefined
                    value set in there
           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: ---

int f(int *p, bool cond)
{
  int i;
  int *q;
  if (cond)
    q =3D &i;
  else
    q =3D p;
  return *q + *p;
}

This can be optimized to `return (*p) * 2;`. This transformation is done by
LLVM, but not by GCC.=