[Bug c/17564] New: [4.0 Regression] New treatment of function pointers when used with equality operators

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

As a GCC extension, GCC allows the comparison of a function pointer and
a void pointer.  Previous versions of GCC didn't canonicalize the function
pointer when it was compared with a void pointer.  Unfortunately, there
doesn't appear to be any documentation on when canonicalization is
performed.

Now GCC canonicalizes the function pointer when compared with a void
pointer.  It even does so when the function pointer is cast to a void
pointer.  The following program demonstrates the problem:

void *f (void) __attribute__ ((__noinline__));
void *
f (void)
{
  return f;
}
int
main (void)
{
  if (f () != f)
    abort ();
  exit (0);
}

000105b4 <main>:
   105b4:       6b c2 3f d9     stw rp,-14(,sp)
   105b8:       e8 5f 1f d5     b,l 105a8 <f>,rp
   105bc:       6f c4 01 00     stw,ma r4,80(,sp)
   105c0:       08 1c 02 44     copy ret0,r4
   105c4:       23 88 10 00     ldil 10800,ret0
   105c8:       e8 40 00 60     b,l 10600 <__canonicalize_funcptr_for_compare>,r
p
   105cc:       4b 9a 02 b0     ldw 158(,ret0),r26
   105d0:       80 9c 20 0a     cmpb,=,n ret0,r4,105dc <main+0x28>
   105d4:       e8 5f 1d 5d     b,l 10488 <_end_init+0x24>,rp


The address of the function descriptor for f is passed to
__canonicalize_funcptr_for_compare for canonicalization whereas the pointer
passed back from f as a void pointer is not canonicalized.  The causes
the program to abort with the current 4.0 CVS source.

The change in function pointer canonicalization causes the testcase
for PR17377 to fail.

-- 
           Summary: [4.0 Regression] New treatment of function pointers when
                    used with equality operators
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: danglin at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: hppa-unknown-linux-gnu
  GCC host triplet: hppa-unknown-linux-gnu
GCC target triplet: hppa-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17564