[Support] Simplify reverseBits with constexpr if (NFC)

Differential Revision: https://reviews.llvm.org/D132814

diff --git a/llvm/include/llvm/Support/MathExtras.h b/llvm/include/llvm/Support/MathExtras.h
index 2b2c47e..b72d483 100644 (file)
--- a/llvm/include/llvm/Support/MathExtras.h
+++ b/llvm/include/llvm/Support/MathExtras.h
@@ -296,45 +296,33 @@ static const unsigned char BitReverseTable256[256] = {
 };
 
 /// Reverse the bits in \p Val.
-template <typename T>
-T reverseBits(T Val) {
-  unsigned char in[sizeof(Val)];
-  unsigned char out[sizeof(Val)];
-  std::memcpy(in, &Val, sizeof(Val));
-  for (unsigned i = 0; i < sizeof(Val); ++i)
-    out[(sizeof(Val) - i) - 1] = BitReverseTable256[in[i]];
-  std::memcpy(&Val, out, sizeof(Val));
-  return Val;
-}
-
+template <typename T> T reverseBits(T Val) {
 #if __has_builtin(__builtin_bitreverse8)
-template<>
-inline uint8_t reverseBits<uint8_t>(uint8_t Val) {
-  return __builtin_bitreverse8(Val);
-}
+  if constexpr (std::is_same_v<T, uint8_t>)
+    return __builtin_bitreverse8(Val);
 #endif
-
 #if __has_builtin(__builtin_bitreverse16)
-template<>
-inline uint16_t reverseBits<uint16_t>(uint16_t Val) {
-  return __builtin_bitreverse16(Val);
-}
+  if constexpr (std::is_same_v<T, uint16_t>)
+    return __builtin_bitreverse16(Val);
 #endif
-
 #if __has_builtin(__builtin_bitreverse32)
-template<>
-inline uint32_t reverseBits<uint32_t>(uint32_t Val) {
-  return __builtin_bitreverse32(Val);
-}
+  if constexpr (std::is_same_v<T, uint32_t>)
+    return __builtin_bitreverse32(Val);
 #endif
-
 #if __has_builtin(__builtin_bitreverse64)
-template<>
-inline uint64_t reverseBits<uint64_t>(uint64_t Val) {
-  return __builtin_bitreverse64(Val);
-}
+  if constexpr (std::is_same_v<T, uint64_t>)
+    return __builtin_bitreverse64(Val);
 #endif
 
+  unsigned char in[sizeof(Val)];
+  unsigned char out[sizeof(Val)];
+  std::memcpy(in, &Val, sizeof(Val));
+  for (unsigned i = 0; i < sizeof(Val); ++i)
+    out[(sizeof(Val) - i) - 1] = BitReverseTable256[in[i]];
+  std::memcpy(&Val, out, sizeof(Val));
+  return Val;
+}
+
 // 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.