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

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


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Comment at: llvm/include/llvm/Support/MathExtras.h:192
     unsigned long Index;
     _BitScanReverse(&Index, Val);
     return Index ^ 31;
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gAlfonso-bit wrote:
> craig.topper wrote:
> > gAlfonso-bit wrote:
> > > 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
> > I tried it on godbolt and it didn't seem to work. Am I doing something wrong? https://godbolt.org/z/MnEY763E4
> Not sure, but so far LLVM compiles on Windows without a hitch, and the testbot is not having issues either
Maybe that just means llvm never uses it in a context where it needs to be evaluated as a constexpr since your patch didn't add any new usages. So it might fail if someone tries to use the constexpr capability?


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D107240/new/

https://reviews.llvm.org/D107240