[PATCH] D136158: [AArch64] Adjust operand sequence for Add+Sub to combine more inline shift

Mon Oct 24 14:05:28 PDT 2022

dmgreen added a comment.

In D136158#3878631 <https://reviews.llvm.org/D136158#3878631>, @bcl5980 wrote:

> In D136158#3878602 <https://reviews.llvm.org/D136158#3878602>, @dmgreen wrote:
>
>> Have you tried testing this? I think it will get stuck in DAG combines.
>>
>> Otherwise the idea sounds good. Have you considered doing it for GlobalISel, or in a way that GlobalISel would also benefit?
>
> I haven't found any stuck in DAG combine local and it looks all of the premerge test is also passed:
> https://reviews.llvm.org/harbormaster/build/291788/
>
> Which combination do you think will cause the dead loop in DAG combine with this patch? I can try to create a test for that.

Yes - the llvm regression tests are very much a subset of all the patterns that can come up in practice. I'm not sure what this is running into. Perhaps try and bootstrap or compiling the llvm-test-suite?

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  https://reviews.llvm.org/D136158/new/

https://reviews.llvm.org/D136158