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Request LLVM to implement _CountLeadingZeros and _CountLeadingZeros64 when targeting ARM/ARM64 #1586

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cbezault opened this issue Jan 24, 2021 · 5 comments · Fixed by #4947
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Request LLVM to implement _CountLeadingZeros and _CountLeadingZeros64 when targeting ARM/ARM64 #1586

cbezault opened this issue Jan 24, 2021 · 5 comments · Fixed by #4947
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ARM Related to the 32-bit ARM architecture ARM64 Related to the ARM64 architecture enhancement Something can be improved fixed Something works now, yay!

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@cbezault
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Currently LLVM does not define the MSVC builtins _CountLeadingZeros and _CountLeadingZeros64 when targeting ARM/ARM64. This forces us to maintain a parallel code path in <bit> for LLVM targeting ARM.

We should make a bug/feature request asking the LLVM devs to implement these builtins when targeting ARM/ARM64.
@cbezault cbezault added enhancement Something can be improved ARM Related to the 32-bit ARM architecture ARM64 Related to the ARM64 architecture labels Jan 24, 2021
@AraHaan
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AraHaan commented Feb 9, 2021

Why not request it now?

@AlexGuteniev
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Can you use __builtin_clz / __builtin_clzll?

https://godbolt.org/z/G4cdsz

@AlexGuteniev
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Ah, you use them already, but want to get rid of this separation

@AraHaan
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AraHaan commented Feb 16, 2021

Why not alias those as _ClountLeadingZeros and _CountLeadingZeros64 on clang when using ARM / ARM64 instead?

@frederick-vs-ja
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LLVM-66554 added these intrinsics to Clang 18.

@StephanTLavavej StephanTLavavej mentioned this issue Feb 21, 2024
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@StephanTLavavej StephanTLavavej mentioned this issue Sep 11, 2024
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@StephanTLavavej StephanTLavavej added the fixed Something works now, yay! label Sep 12, 2024
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ARM Related to the 32-bit ARM architecture ARM64 Related to the ARM64 architecture enhancement Something can be improved fixed Something works now, yay!
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Toolset update: VS 2022 17.12 Preview 2, Clang 18.1.8 StephanTLavavej/STL
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@cbezault @AlexGuteniev @StephanTLavavej @AraHaan @frederick-vs-ja