[PATCH] D139275: [SimplifyCFG] `FoldBranchToCommonDest()`: deal with mismatched IV's in PHI's in common successor block

Fri Dec 16 08:59:55 PST 2022

lebedev.ri added a comment.

In D139275#4001628 <https://reviews.llvm.org/D139275#4001628>, @alexfh wrote:

> In D139275#4001603 <https://reviews.llvm.org/D139275#4001603>, @lebedev.ri wrote:
>
>> In D139275#4001601 <https://reviews.llvm.org/D139275#4001601>, @alexfh wrote:
>>
>>> I will revert this patch. Please ensure the provided test case works fine before recommitting.
>>
>> Thanks for the reproducer. Will revert in a sec.
>
> I've done that already. I had a revert prepared with conflict resolutions for the opaque pointers migration.

So. There is a problem.
Before the patch, this is what we got: https://alive2.llvm.org/ce/z/WMZXQu <-- good
With the patch, we'd get: https://alive2.llvm.org/ce/z/oBg872 <-- miscompile
BUT. If we **just** run simplifycfg on the old result, we get: https://alive2.llvm.org/ce/z/zb7bsb <-- good!
So the actual miscompile is elsewhere.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D139275/new/

https://reviews.llvm.org/D139275