[llvm] [SCEV] Use power of two facts involving vscale when inferring wrap flags (PR #101380)

[Nikita Popov via llvm-commits]

================
@@ -12775,8 +12792,7 @@ ScalarEvolution::howManyLessThans(const SCEV *LHS, const SCEV *RHS,
     if (!isLoopInvariant(RHS, L))
       return false;
 
-    auto *StrideC = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*this));
-    if (!StrideC || !StrideC->getAPInt().isPowerOf2())
+    if (!isKnownToBeAPowerOfTwo(AR->getStepRecurrence(*this), true))
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nikic wrote:

```suggestion
    if (!isKnownToBeAPowerOfTwo(AR->getStepRecurrence(*this), /*OrZero=*/true))
```

https://github.com/llvm/llvm-project/pull/101380