[Bug middle-end/34971] New: bitfield rotates are folded and expanded wrong

[rguenth at gcc dot gnu dot org]

struct foo
{
  unsigned long long b:40;
} x;

extern void abort (void);

void test1(unsigned long long res)
{
  /* Build a rotate expression on a 40 bit argument.  */
  if ((x.b<<8) + (x.b>>32) != res)
    abort ();
}

int main()
{
  x.b = 0x0100000001;
  test1(0x0000000101);
  x.b = 0x0100000000;
  test1(0x0000000001);
  return 0;
}

Patch to fix the most obvious problems:

http://gcc.gnu.org/ml/gcc-patches/2008-01/msg01224.html

the (maybe better) alternative is to not allow ROTATE_EXPRs that
operate on entities whose precision doesn't match their modes bitsize.


-- 
           Summary: bitfield rotates are folded and expanded wrong
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34971