[libc][__support][bit] remove compiler has builtin checks

[nickdesaulniers]

We only support building llvmlibc with modern compilers.
https://libc.llvm.org/compiler_support.html#minimum-supported-versions

All versions of the these compilers support these builtins; GCC does not
support the short variants.

[llvmbot]

@llvm/pr-subscribers-libc

Author: Nick Desaulniers (nickdesaulniers)

Changes

We only support building llvmlibc with modern compilers.
https://libc.llvm.org/compiler_support.html#minimum-supported-versions

All versions of the these compilers support these builtins; GCC does not
support the short variants.

---

Full diff: https://github.com/llvm/llvm-project/pull/81679.diff

1 Files Affected:

• (modified) libc/src/__support/CPP/bit.h (-18)

diff --git a/libc/src/__support/CPP/bit.h b/libc/src/__support/CPP/bit.h
index 392fbe248138ae..a8bf75a9a2efac 100644
--- a/libc/src/__support/CPP/bit.h
+++ b/libc/src/__support/CPP/bit.h
@@ -93,15 +93,9 @@ template <typename T, typename = cpp::enable_if_t<cpp::is_unsigned_v<T>>>
 #if LIBC_HAS_BUILTIN(__builtin_ctzs)
 ADD_SPECIALIZATION(countr_zero, unsigned short, __builtin_ctzs)
 #endif
-#if LIBC_HAS_BUILTIN(__builtin_ctz)
 ADD_SPECIALIZATION(countr_zero, unsigned int, __builtin_ctz)
-#endif
-#if LIBC_HAS_BUILTIN(__builtin_ctzl)
 ADD_SPECIALIZATION(countr_zero, unsigned long, __builtin_ctzl)
-#endif
-#if LIBC_HAS_BUILTIN(__builtin_ctzll)
 ADD_SPECIALIZATION(countr_zero, unsigned long long, __builtin_ctzll)
-#endif
 
 /// Count number of 0's from the most significant bit to the least
 ///   stopping at the first 1.
@@ -128,15 +122,9 @@ template <typename T, typename = cpp::enable_if_t<cpp::is_unsigned_v<T>>>
 #if LIBC_HAS_BUILTIN(__builtin_clzs)
 ADD_SPECIALIZATION(countl_zero, unsigned short, __builtin_clzs)
 #endif
-#if LIBC_HAS_BUILTIN(__builtin_clz)
 ADD_SPECIALIZATION(countl_zero, unsigned int, __builtin_clz)
-#endif
-#if LIBC_HAS_BUILTIN(__builtin_clzl)
 ADD_SPECIALIZATION(countl_zero, unsigned long, __builtin_clzl)
-#endif
-#if LIBC_HAS_BUILTIN(__builtin_clzll)
 ADD_SPECIALIZATION(countl_zero, unsigned long long, __builtin_clzll)
-#endif
 
 #undef ADD_SPECIALIZATION
 
@@ -256,15 +244,9 @@ template <typename T, typename = cpp::enable_if_t<cpp::is_unsigned_v<T>>>
 #if LIBC_HAS_BUILTIN(__builtin_clzs)
 SPECIALIZE_FLZ(first_leading_zero, unsigned short, __builtin_clzs)
 #endif
-#if LIBC_HAS_BUILTIN(__builtin_clz)
 SPECIALIZE_FLZ(first_leading_zero, unsigned int, __builtin_clz)
-#endif
-#if LIBC_HAS_BUILTIN(__builtin_clzl)
 SPECIALIZE_FLZ(first_leading_zero, unsigned long, __builtin_clzl)
-#endif
-#if LIBC_HAS_BUILTIN(__builtin_clzll)
 SPECIALIZE_FLZ(first_leading_zero, unsigned long long, __builtin_clzll)
-#endif
 
 #undef SPECIALIZE_FLZ
 

[michaelrj-google]

I'm fine with doing this conceptually, but have you tested it on arm and risc-v? Sometimes the compilers for those are missing builtins unexpectedly

[gchatelet]

It seems to be OK for all the compilers and environments we support.
https://godbolt.org/z/Ez3jaxKqz