MathExtras: Make some templates constexpr NFC (#145522)

so that they can be evaluated at compiler time (we can see these values
in hover via clangd).

Author: hokein

llvm/include/llvm/Support/MathExtras.h

@@ -79,7 +79,7 @@ constexpr float ef          = 0x1.5bf0a8P+1F, // (2.71828183) https://oeis.org/A
 
 /// Create a bitmask with the N right-most bits set to 1, and all other
 /// bits set to 0.  Only unsigned types are allowed.
-template <typename T> T maskTrailingOnes(unsigned N) {
+template <typename T> constexpr T maskTrailingOnes(unsigned N) {
   static_assert(std::is_unsigned_v<T>, "Invalid type!");
   const unsigned Bits = CHAR_BIT * sizeof(T);
   assert(N <= Bits && "Invalid bit index");
@@ -90,19 +90,19 @@ template <typename T> T maskTrailingOnes(unsigned N) {
 
 /// Create a bitmask with the N left-most bits set to 1, and all other
 /// bits set to 0.  Only unsigned types are allowed.
-template <typename T> T maskLeadingOnes(unsigned N) {
+template <typename T> constexpr T maskLeadingOnes(unsigned N) {
   return ~maskTrailingOnes<T>(CHAR_BIT * sizeof(T) - N);
 }
 
 /// Create a bitmask with the N right-most bits set to 0, and all other
 /// bits set to 1.  Only unsigned types are allowed.
-template <typename T> T maskTrailingZeros(unsigned N) {
+template <typename T> constexpr T maskTrailingZeros(unsigned N) {
   return maskLeadingOnes<T>(CHAR_BIT * sizeof(T) - N);
 }
 
 /// Create a bitmask with the N left-most bits set to 0, and all other
 /// bits set to 1.  Only unsigned types are allowed.
-template <typename T> T maskLeadingZeros(unsigned N) {
+template <typename T> constexpr T maskLeadingZeros(unsigned N) {
   return maskTrailingOnes<T>(CHAR_BIT * sizeof(T) - N);
 }
 
@@ -120,7 +120,7 @@ static const unsigned char BitReverseTable256[256] = {
 };
 
 /// Reverse the bits in \p Val.
-template <typename T> T reverseBits(T Val) {
+template <typename T> constexpr T reverseBits(T Val) {
 #if __has_builtin(__builtin_bitreverse8)
   if constexpr (std::is_same_v<T, uint8_t>)
     return __builtin_bitreverse8(Val);
@@ -217,7 +217,7 @@ constexpr bool isShiftedUInt(uint64_t x) {
 }
 
 /// Gets the maximum value for a N-bit unsigned integer.
-inline uint64_t maxUIntN(uint64_t N) {
+inline constexpr uint64_t maxUIntN(uint64_t N) {
   assert(N <= 64 && "integer width out of range");
 
   // uint64_t(1) << 64 is undefined behavior, so we can't do
@@ -233,7 +233,7 @@ inline uint64_t maxUIntN(uint64_t N) {
 }
 
 /// Gets the minimum value for a N-bit signed integer.
-inline int64_t minIntN(int64_t N) {
+inline constexpr int64_t minIntN(int64_t N) {
   assert(N <= 64 && "integer width out of range");
 
   if (N == 0)
@@ -242,7 +242,7 @@ inline int64_t minIntN(int64_t N) {
 }
 
 /// Gets the maximum value for a N-bit signed integer.
-inline int64_t maxIntN(int64_t N) {
+inline constexpr int64_t maxIntN(int64_t N) {
   assert(N <= 64 && "integer width out of range");
 
   // This relies on two's complement wraparound when N == 64, so we convert to
@@ -253,12 +253,12 @@ inline int64_t maxIntN(int64_t N) {
 }
 
 /// Checks if an unsigned integer fits into the given (dynamic) bit width.
-inline bool isUIntN(unsigned N, uint64_t x) {
+inline constexpr bool isUIntN(unsigned N, uint64_t x) {
   return N >= 64 || x <= maxUIntN(N);
 }
 
 /// Checks if an signed integer fits into the given (dynamic) bit width.
-inline bool isIntN(unsigned N, int64_t x) {
+inline constexpr bool isIntN(unsigned N, int64_t x) {
   return N >= 64 || (minIntN(N) <= x && x <= maxIntN(N));
 }