[Bug tree-optimization/51683] New: [4.7 Regression] __builtin_memcpy etc. with constant first argument optimized away by ccp

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51683

             Bug #: 51683
           Summary: [4.7 Regression] __builtin_memcpy etc. with constant
                    first argument optimized away by ccp
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: jakub@gcc.gnu.org
        ReportedBy: jakub@gcc.gnu.org


static inline void *
bar (void *p, void *q, int r)
{
  return __builtin_memcpy (p, q, r);
}

void *
foo (void *p)
{
  return bar ((void *) 0x12345000, p, 256);
}

at -O2 starting with http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=175290
is optimized away.  While the return value from memcpy is known to be constant
and we know that constant, we ignore the other side-effects of the call.