[llvm] [LangRef] Require that vscale be a power of two (PR #145098)

[Nikita Popov via llvm-commits]

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@@ -4660,7 +4660,6 @@ bool SelectionDAG::isKnownToBeAPowerOfTwo(SDValue Val, unsigned Depth) const {
 
   // vscale(power-of-two) is a power-of-two for some targets
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nikic wrote:

```suggestion
  // vscale(power-of-two) is a power-of-two
```

https://github.com/llvm/llvm-project/pull/145098