https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66090
Richard Earnshaw <rearnsha at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |UNCONFIRMED
CC| |rguenth at gcc dot gnu.org
Resolution|INVALID |---
--- Comment #3 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> Since the pointer is wrapping to null, you need to use
> -fno-delete-null-pointer-checks to disable removing of checks of null
> pointers or rather it enables allowing pointers to wrap to become null.
> In C, once a pointer is non-null, it can't become null by adding a value to
> it. So GCC enables an optimization around that case (and
> fno-delete-null-pointer-checks disables that optimization).
>
> So no GCC bug, just wrongly assuming pointers can't become null pointers if
> they were not null pointers.
I'm inclined to disagree.
Firstly, the code does not check for a null pointer, it checks a loop iterator
variable.
Secondly, although the pointer value wraps to zero, that value is never
dereferenced; the last memory access is at 0xfffffffc.
So I think the compiler is incorrectly removing a valid termination check.
Richi, I'd like your opinion on this one.
