[Bug tree-optimization/83311] Unable to optimize alloc calls with casts and string builtins

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83311

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2017-12-07
            Version|unknown                     |8.0
         Depends on|                            |82991
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
While I could special-case this it really depends on PR82991.  The issue is we
see

  <bb 2> :
  s_5 = __builtin_alloca (1);
  _1 = __builtin_memcpy (s_5, "a", 1);
  _2 = MEM[(char *)_1];
  _7 = (int) _2;
  return _7;

thus we read from _1 but we memcpy to s_5.  One might consider it a duplicate
of that PR even.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82991
[Bug 82991] memcpy and strcpy return value can be assumed to be equal to first
argument