[llvm] [ADT] Add llvm::countr_zero_constexpr (PR #164188)

[Jakub Kuderski via llvm-commits]

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@@ -177,6 +178,22 @@ template <typename T> [[nodiscard]] inline int popcount(T Value) noexcept {
   }
 }
 
+/// Count number of 0's from the least significant bit to the most
+///   stopping at the first 1.
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kuhar wrote:

This indentation looks weird

https://github.com/llvm/llvm-project/pull/164188