[PATCH] D110620: [SCEV] Infer ranges for SCC consisting of cycled Phis

Wed Jul 13 02:02:22 PDT 2022

mkazantsev added a comment.

In D110620#3361521 <https://reviews.llvm.org/D110620#3361521>, @aeubanks wrote:

> I'm seeing a miscompile caused by assuming the entire SCC has the same range. One phi in the SCC has a corresponding `llvm.assume` limiting its range, but that assume doesn't apply to another phi in the SCC.
>
> I apologize for the fairly large repro (at least it's only one function!).
> `$ opt -passes=indvars test.ll -S`
> You'll see that the `br` condition right before the `invoke i32 @wobble.7` becomes `false`. That's because `%tmp951` has a corresponding assume that it's non-negative. However, `%tmp298`, which is in the same phi SCC, is not under that assumption, but this patch still updates its range to be non-negative.
>
> F22331869: test.ll <https://reviews.llvm.org/F22331869>

Taking a look...

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  https://reviews.llvm.org/D110620/new/

https://reviews.llvm.org/D110620