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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/63989] tree-ssa-strlen.c doesn't handle constant pointer plus and array refs if constant offset is smaller than known constant string length
Date: Thu, 20 Nov 2014 09:44:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63989

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-11-20
     Ever confirmed|0                           |1

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So, we are talking here about e.g.

int
f1 (char *p)
{
  __builtin_strcpy (p, "foobar");
  return __builtin_strlen (p + 2);
}

int
f2 (char *p)
{
  __builtin_strcpy (p, "foobar");
  p[2] = '\0';
  return __builtin_strlen (p);
}

int
f3 (char *p)
{
  __builtin_strcpy (p, "foobar");
  p[2] = '\0';
  return __builtin_strlen (p + 3);
}

int
f4 (char *p)
{
  __builtin_strcpy (p, "foobar");
  p[2] = 'z';
  return __builtin_strlen (p);
}

and then also determining using get_string_length (if constant) whether a
character pointer dereference is known to be zero or known to be non-zero.