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Date: Thu, 27 Jan 2005 19:59:00 -0000
From: "kazu at cs dot umass dot edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20050127195923.19659.kazu@cs.umass.edu>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug tree-optimization/19659] New: GCC does remove an "if" statement that never triggers.
X-Bugzilla-Reason: CC
X-SW-Source: 2005-01/txt/msg04076.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

extern void abort (void) __attribute__ ((__noreturn__));

/* Count up to *LENGTHP and then return 0.  */

int
foo (unsigned *lengthp)
{
  unsigned index;

  for (index = 0; index != *lengthp; index++)
    {
      const unsigned *lengthp2 = lengthp;

      /* Note that this condition is never true.  */
      if (index >= *lengthp2)
	abort ();
    }

  return 0;
}

GCC does not remove the "if" statement even though it never triggers.

Interestingly, if you remove "const" from the testcase above, GCC does
remove the "if" statement.

If you feed the testcase with "const" into GCC, CSE removes it.
Hey, but isn't this a machine-independent optimization?

-- 
           Summary: GCC does remove an "if" statement that never triggers.
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Keywords: missed-optimization, TREE
          Severity: enhancement
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazu at cs dot umass dot edu
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19659