[Bug target/107403] New: uint64_t bitfield operation is mishandled

[Bug target/107403] New: uint64_t bitfield operation is mishandled

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107403

            Bug ID: 107403
           Summary: uint64_t bitfield operation is mishandled
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hjl.tools at gmail dot com
  Target Milestone: ---
            Target: x84

[hjl@gnu-cfl-1 tmp]$ cat foo.c
#include <stdint.h>
#include <stdio.h>

#define VAL (1ULL << 48)

struct foo
{
  uint64_t x : 8;
  uint64_t y : 56;
};

__attribute__ ((noinline))
uint64_t
func (struct foo i)
{
  return i.y << 8ULL;
}

int
main ()
{
  struct foo i;
  i.x = 0;
  i.y = VAL;
  uint64_t x = func (i);
  printf ("0x%llx\n", x);
  printf ("0x%llx\n", VAL);
  if (x != (VAL << 8ULL))
    __builtin_abort ();
}
[hjl@gnu-cfl-1 tmp]$ gcc foo.c
[hjl@gnu-cfl-1 tmp]$ ./a.out 
0x0
0x1000000000000
Aborted (core dumped)
[hjl@gnu-cfl-1 tmp]$

[Bug target/107403] uint64_t bitfield operation is mishandled

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107403

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
No this is correct.
i.y << 8ULL
Is all done in 56bit type as the type is greater than the size of int.

Note c allows this behavior while c++ does not.

[Bug target/107403] uint64_t bitfield operation is mishandled

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107403

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note gcc and clang have different implementation defined behavior here too.

[Bug target/107403] uint64_t bitfield operation is mishandled

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107403

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=92684
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup of bug 94631.

*** This bug has been marked as a duplicate of bug 94631 ***

[Bug target/107403] uint64_t bitfield operation is mishandled

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107403

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
See https://gcc.gnu.org/legacy-ml/gcc/2017-10/msg00192.html