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SCEV tries to constant-fold arguments of trunc operands in SCEVAddExpr, and when it does that, it passes wrong flags into the recursion. It is only valid to pass flags that are proved for narrow type into a computation in wider type if we can prove that trunc instruction doesn't actually change the value. If it did lose some meaningful bits, we may end up proving wrong no-wrap flags for sum of arguments of trunc. In the provided test we end up with `nuw` where it shouldn't be because of this bug. The solution is to conservatively pass `SCEV::FlagAnyWrap` which is always a valid thing to do. Reviewed By: sanjoy Differential Revision: https://reviews.llvm.org/D49471 llvm-svn: 337435
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