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[libc++] Replace uses of __libcpp_ctz by __countr_zero #131179

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ldionne opened this issue Mar 13, 2025 · 0 comments · Fixed by #133920
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[libc++] Replace uses of __libcpp_ctz by __countr_zero #131179

ldionne opened this issue Mar 13, 2025 · 0 comments · Fixed by #133920
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libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi.

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ldionne commented Mar 13, 2025 •
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For a follow-up patch, we should replace uses of __libcpp_ctz in the codebase by calls to __countr_zero (there's only a few). This will eventually allow us to clean up __libcpp_ctz altogether.

Originally posted by @ldionne in #122641 (comment)
@llvmbot llvmbot added the libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. label Mar 13, 2025
@PaulXiCao PaulXiCao mentioned this issue Mar 23, 2025
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@winner245 winner245 mentioned this issue Apr 1, 2025
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IanWood1 pushed a commit to IanWood1/llvm-project that referenced this issue May 6, 2025
@winner245 @IanWood1
[libc++] Replace __libcpp_{ctz, clz} with __builtin_{ctzg, clzg} (llv…
293a7d7 
…m#133920)

`__libcpp_{ctz, clz}` were previously used as fallbacks for `__builtin_{ctzg, clzg}` to ensure compatibility with older compilers (Clang 18 and earlier), as `__builtin_{ctzg, clzg}` became available in Clang 19. Now that support for Clang 18 has been officially dropped in llvm#130142, we can now safely  replace all instances of `__libcpp_{ctz, clz}` with `__count{l,r}_zero` (which internally call `__builtin_{ctzg, clzg}` and eliminate the fallback logic.

Closes llvm#131179.
IanWood1 pushed a commit to IanWood1/llvm-project that referenced this issue May 6, 2025
@winner245 @IanWood1
[libc++] Replace __libcpp_{ctz, clz} with __builtin_{ctzg, clzg} (llv…
df3b550 
…m#133920)

`__libcpp_{ctz, clz}` were previously used as fallbacks for `__builtin_{ctzg, clzg}` to ensure compatibility with older compilers (Clang 18 and earlier), as `__builtin_{ctzg, clzg}` became available in Clang 19. Now that support for Clang 18 has been officially dropped in llvm#130142, we can now safely  replace all instances of `__libcpp_{ctz, clz}` with `__count{l,r}_zero` (which internally call `__builtin_{ctzg, clzg}` and eliminate the fallback logic.

Closes llvm#131179.
IanWood1 pushed a commit to IanWood1/llvm-project that referenced this issue May 6, 2025
@winner245 @IanWood1
[libc++] Replace __libcpp_{ctz, clz} with __builtin_{ctzg, clzg} (llv…
f827de6 
…m#133920)

`__libcpp_{ctz, clz}` were previously used as fallbacks for `__builtin_{ctzg, clzg}` to ensure compatibility with older compilers (Clang 18 and earlier), as `__builtin_{ctzg, clzg}` became available in Clang 19. Now that support for Clang 18 has been officially dropped in llvm#130142, we can now safely  replace all instances of `__libcpp_{ctz, clz}` with `__count{l,r}_zero` (which internally call `__builtin_{ctzg, clzg}` and eliminate the fallback logic.

Closes llvm#131179.
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