Support: Add specializations for reverseBits to use builtin

llvm/include/llvm/Support/MathExtras.h

@@ -313,6 +313,34 @@ T reverseBits(T Val) {
   return Val;
 }
 
+#if __has_builtin(__builtin_bitreverse8)
+template<>
+inline uint8_t reverseBits<uint8_t>(uint8_t Val) {
+  return __builtin_bitreverse8(Val);
+}
+#endif
+
+#if __has_builtin(__builtin_bitreverse16)
+template<>
+inline uint16_t reverseBits<uint16_t>(uint16_t Val) {
+  return __builtin_bitreverse16(Val);
+}
+#endif
+
+#if __has_builtin(__builtin_bitreverse32)
+template<>
+inline uint32_t reverseBits<uint32_t>(uint32_t Val) {
+  return __builtin_bitreverse32(Val);
+}
+#endif
+
+#if __has_builtin(__builtin_bitreverse64)
+template<>
+inline uint64_t reverseBits<uint64_t>(uint64_t Val) {
+  return __builtin_bitreverse64(Val);
+}
+#endif
+
 // NOTE: The following support functions use the _32/_64 extensions instead of
 // type overloading so that signed and unsigned integers can be used without
 // ambiguity.