[libc-commits] [libc] [libc][support][bit] use new type generic builtins (PR #86746)

[Nick Desaulniers via libc-commits]

https://github.com/nickdesaulniers updated https://github.com/llvm/llvm-project/pull/86746

>From a23d6d445b699be666a781f22673e36ca465fe77 Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers at google.com>
Date: Mon, 25 Mar 2024 11:28:35 -0700
Subject: [PATCH 1/2] [libc][support][bit] use new type generic builtins

These are new in clang-19+, gcc-14+.
---
 libc/src/__support/CPP/bit.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/libc/src/__support/CPP/bit.h b/libc/src/__support/CPP/bit.h
index 80f50fd221efa7..68b4acf8bc5f5e 100644
--- a/libc/src/__support/CPP/bit.h
+++ b/libc/src/__support/CPP/bit.h
@@ -72,6 +72,14 @@ has_single_bit(T value) {
 /// Only unsigned integral types are allowed.
 ///
 /// Returns cpp::numeric_limits<T>::digits on an input of 0.
+// clang-19+, gcc-14+
+#if __has_builtin(__builtin_ctzg)
+template <typename T>
+[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
+countr_zero(T value) {
+  return __builtin_ctzg(value, cpp::numeric_limits<T>::digits);
+}
+#else
 template <typename T>
 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
 countr_zero(T value) {
@@ -99,6 +107,7 @@ ADD_SPECIALIZATION(countr_zero, unsigned short, __builtin_ctzs)
 ADD_SPECIALIZATION(countr_zero, unsigned int, __builtin_ctz)
 ADD_SPECIALIZATION(countr_zero, unsigned long, __builtin_ctzl)
 ADD_SPECIALIZATION(countr_zero, unsigned long long, __builtin_ctzll)
+#endif // __has_builtin(__builtin_ctzg)
 
 /// Count number of 0's from the most significant bit to the least
 ///   stopping at the first 1.
@@ -106,9 +115,17 @@ ADD_SPECIALIZATION(countr_zero, unsigned long long, __builtin_ctzll)
 /// Only unsigned integral types are allowed.
 ///
 /// Returns cpp::numeric_limits<T>::digits on an input of 0.
+// clang-19+, gcc-14+
+#if __has_builtin(__builtin_clzg)
 template <typename T>
 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
 countl_zero(T value) {
+  return __builtin_clzg(value, cpp::numeric_limits<T>::digits);
+}
+#else
+template <typename T [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<
+    cpp::is_unsigned_v<T>, int>
+              countl_zero(T value) {
   if (!value)
     return cpp::numeric_limits<T>::digits;
   // Bisection method.
@@ -129,6 +146,7 @@ ADD_SPECIALIZATION(countl_zero, unsigned short, __builtin_clzs)
 ADD_SPECIALIZATION(countl_zero, unsigned int, __builtin_clz)
 ADD_SPECIALIZATION(countl_zero, unsigned long, __builtin_clzl)
 ADD_SPECIALIZATION(countl_zero, unsigned long long, __builtin_clzll)
+#endif // __has_builtin(__builtin_clzg)
 
 #undef ADD_SPECIALIZATION
 

>From a692e2ca3883ded2dcbce73313200730d5c796dc Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers at google.com>
Date: Fri, 5 Apr 2024 10:01:20 -0700
Subject: [PATCH 2/2] fix typo, missed a closing angle bracket

---
 libc/src/__support/CPP/bit.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/libc/src/__support/CPP/bit.h b/libc/src/__support/CPP/bit.h
index 68b4acf8bc5f5e..8a8951a18bfa1b 100644
--- a/libc/src/__support/CPP/bit.h
+++ b/libc/src/__support/CPP/bit.h
@@ -123,9 +123,9 @@ countl_zero(T value) {
   return __builtin_clzg(value, cpp::numeric_limits<T>::digits);
 }
 #else
-template <typename T [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<
-    cpp::is_unsigned_v<T>, int>
-              countl_zero(T value) {
+template <typename T>
+[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
+countl_zero(T value) {
   if (!value)
     return cpp::numeric_limits<T>::digits;
   // Bisection method.