[Bug target/77687] frame access after release without redzone on powerpc

segher at gcc dot gnu.org gcc-bugzilla@gcc.gnu.org
Mon Nov 20 20:11:00 GMT 2017


--- Comment #8 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Author: segher
Date: Mon Nov 20 20:10:28 2017
New Revision: 254968

URL: https://gcc.gnu.org/viewcvs?rev=254968&root=gcc&view=rev
rs6000: Don't touch below the stack pointer (PR77687)

With the 32-bit SVR4 ABI we don't have a red zone, so we have to restore
the callee-saved registers before we restore the stack pointer.

The previous fix for this PR failed in two ways, for huge frames: first,
we use a negative offset from r11 in that case, so the (mem:BLK 11) access
does no good; second, sched does not handle accesses to mem:BLK correctly
in this case (does not make dependencies).

This patch fixes it by doing a store to (mem:BLK (scratch)) instead.
This means no unrelated (not to stack) loads/stores can be moved over the
stack restore either, but so be it.

        PR target/77687
        * config/rs6000/rs6000.md (stack_restore_tie): Store to a scratch
        address instead of to r1 and r11.

        PR target/77687
        * gcc.target/powerpc/pr77687.c: New testcase.


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