[PATCH] D107240: [LLVM][NFC] Make multiple bitwise MathExtras functions constexpr

Alf via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Wed Aug 4 16:15:59 PDT 2021


gAlfonso-bit marked an inline comment as done.
gAlfonso-bit added inline comments.


================
Comment at: llvm/include/llvm/Support/MathExtras.h:192
     unsigned long Index;
     _BitScanReverse(&Index, Val);
     return Index ^ 31;
----------------
craig.topper wrote:
> Does _BitScanReverse work in a constexpr in MSVC? The implementation in clang-cl doesn't work in constexpr, but clang-cl would use __builtin_clz.
Yes it does. This is one of those exceptions where you can pass a reference because you don't read Index, but only write to it, and Index is in a constexpr anyway


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