[llvm] MathExtras: rewrite some methods to never overflow (PR #95556)

[Jay Foad via llvm-commits]

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@@ -385,6 +385,8 @@ inline uint64_t PowerOf2Ceil(uint64_t A) {
 ///   alignTo(~0LL, 8) = 0
 ///   alignTo(321, 255) = 510
 /// \endcode
+///
+/// May overflow.
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jayfoad wrote:

Sure. It is a pre-existing problem. No need to fix it right now.

https://github.com/llvm/llvm-project/pull/95556