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

Fri Mar 4 19:54:02 PST 2022

aeubanks added a comment.
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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>

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Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:6693-6698
+    if (I == Cache.end())
+      setRange(PNSCEV, SignHint, ConservativeResult);
+    else {
+      auto SharpenedRange =
+          I->second.intersectWith(ConservativeResult, RangeType);
+      setRange(PNSCEV, SignHint, SharpenedRange);
----------------
Here

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

https://reviews.llvm.org/D110620