[Bug rtl-optimization/125728] [16/17 Regression] M68k: m68k-elf-gcc generates code that raises address error exception in certain circumstances

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125728

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=120329

--- Comment #4 from Drea Pinski <pinskia at gcc dot gnu.org> ---
There is code in validate_subreg which is designed to reject some of this BUT
it looks like misses the issue with big-endian needing a negative offset for
big-endian which causes the alignment check to be not be good enough:

```
  /* Do not allow normal SUBREG with stricter alignment than the inner MEM.

     PR120329: Combine can create paradoxical mem subregs even for
     strict-alignment targets.  Allow it until combine is fixed.  */
  else if (reg && MEM_P (reg) && STRICT_ALIGNMENT
           && MEM_ALIGN (reg) < GET_MODE_ALIGNMENT (omode)
           && known_le (osize, isize))
    return false;
```