On Fri, Dec 10, 2021 at 2:30 AM Roger Sayle <ro...@nextmovesoftware.com> wrote:
>
>
> This patch fixes PR ipa/103061 which is P1 regression that shows up as
> an ICE in ipa-modref-tree.c's insert_kill when compiling the CSiBE
> benchmark. I believe the underlying cause is that the new kill tracking
> functionality wasn't anticipating memory accesses that are zero bits
> wide!?. The failing source code (test case) contains the unusual lines:
> typedef struct { } spinlock_t;
> and
> q->lock = (spinlock_t) { };
> Making spinlock_t larger, or removing the assignment work around the issue.
zero sized accesses (load and stores) should have been removed during
gimplification. Why was it not?
Thanks,
Andrew
>
> The one line patch below to useful_for_kill_p teaches IPA that a memory
> write is only useful as a "kill" if it is more than zero bits wide.
> In theory, the existing known_size_p (size) test is now redundant, as
> poly_int64 currently uses the value -1 for unknown size values,
> but the proposed change makes the semantics clear, and defends against
> possible future changes in representation [but I'm happy to change this].
>
> This patch has been tested on x86_64-pc-linux-gnu with a make bootstrap
> and make -k check with no new failures. Ok for mainline?
>
>
> 2021-12-10 Roger Sayle <ro...@nextmovesoftware.com>
>
> gcc/ChangeLog
> PR ipa/103601
> * ipa-modref-tree.h (useful_for_kill_p): Zero width accesses aren't
> useful for kill tracking.
>
> gcc/testsuite/ChangeLog
> PR ipa/103601
> * gcc.dg/ipa/pr103601.c: New test case.
>
> Thanks in advance,
> Roger
> --
>
