[libcxx-commits] [libcxx] [libcxx] Use generic builtins for popcount, clz and ctz (PR #86563)

[Nick Desaulniers via libcxx-commits]

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@@ -47,8 +59,13 @@ inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(__uint128_t __x)
   // - Any bits set:
   //   - The number of leading zeros of the input is the number of leading
   //     zeros in the high 64-bits.
+#  if __has_builtin(__builtin_clzg)
+  return ((__x >> 64) == 0) ? (64 + __builtin_clzg(static_cast<unsigned long long>(__x)))
+                            : __builtin_clzg(static_cast<unsigned long long>(__x >> 64));
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nickdesaulniers wrote:

`__builtin_clzg` can handle `__uint128_t` I suspect.  No need to do any of this.

https://github.com/llvm/llvm-project/pull/86563