[Bug c/40757] gcc 4.4.0 miscompiles mpfr-2.4.1

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

------- Comment #17 from jakub at gcc dot gnu dot org  2009-07-17 07:49 -------
Try:
typedef __SIZE_TYPE__ size_t;
extern void *memset (void *, const void *, size_t);
extern void abort (void);
volatile size_t i = 0x80000000U, j = 0x80000000U;
char buf[16];

int main (void)
{
  if (sizeof (size_t) != 4)
    return 0;
  buf[0] = 6;
  memset (buf, 0, i + j);
  if (buf[0] != 6)
    abort ();
  return 0;
}
In 32-bit code, size_t is 32-bit, memset is called with buf, 0, 0 arguments,
but the %o2 register passed to it doesn't contain 0, but 0x100000000.  That is
fine, this is 32-bit code, so the uppermost bits are always undefined.  But
when 32-bit memset uses brnz %o2, ... instruction, it needs to first
zero-extend it to 64-bits, as brnz operates on all 64 bits only.  Or not use
brnz, but compare and be %icc, ...


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40757