https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78685
Eric Gallager <egallager at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |egallager at gcc dot gnu.org
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=54200
--- Comment #9 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Tom de Vries from comment #8)
> Created attachment 44333 [details]
> proof of concept patch
>
> I ran into the same problem with guality test-case pr54200.c, which fails
> for Og.
>
> The relevant part of the test-case is:
> ...
> int __attribute__((noinline,noclone))
> foo (int z, int x, int b)
> {
> if (x == 1)
> {
> bar ();
> return z;
> }
> else
> {
> int a = (x + z) + b;
> return a; /* { dg-final { gdb-test 20 "z" "3" } } */
> }
> }
> ...
>
> The problem is that the '(x + z) + b' calculation has a temporary register
> which gets allocated the register that holds 'z', so when we get to the
> gdb-test line, z is no longer available.
>
> Using this patch I managed to print the correct value of z at the gdb-test
> line.
>
> The patch uses clobbers in gimple to mark the out-of-scope point, purely
> because that's similar to what was already done for local array variables,
> and I thought that was the fastest path to getting a proof of concept
> working. It's more accurate to model this as some sort of use in gimple, and
> doing so may prevent gimple optimizations which wreck debug info, but
> perhaps that's not necessary, I suppose that depends on which optimizations
> are enabled in Og.
>
> Anyway, at expand we emit a use for the clobber which seems to do the trick.
Please submit the patch to the gcc-patches mailing list for review! Thanks.
