[Support] Remove findFirstSet and findLastSet

[kazu]

Summary

This patch removes findFirstSet and findLastSet as there are no uses
left in LLVM.

I am not aware of any uses of findFirstSet and findLastSet in the
open-source world outside LLVM, so I am skipping the deprecation step.

[dblaikie]

SGTM

llvm/include/llvm/Support/MathExtras.h

 #include <climits>
 #include <cstdint>
 #include <cstring>
 #include <limits>
 #include <type_traits>
 
 namespace llvm {
 
-/// The behavior an operation has on an input of 0.
-enum ZeroBehavior {
-  /// The returned value is undefined.
-  ZB_Undefined,
-  /// The returned value is numeric_limits<T>::max()
-  ZB_Max
-};
-
 /// Mathematical constants.
 namespace numbers {
 // TODO: Track C++20 std::numbers.
 // TODO: Favor using the hexadecimal FP constants (requires C++17).
 constexpr double e          = 2.7182818284590452354, // (0x1.5bf0a8b145749P+1) https://oeis.org/A001113
                  egamma     = .57721566490153286061, // (0x1.2788cfc6fb619P-1) https://oeis.org/A001620
                  ln2        = .69314718055994530942, // (0x1.62e42fefa39efP-1) https://oeis.org/A002162
                  ln10       = 2.3025850929940456840, // (0x1.24bb1bbb55516P+1) https://oeis.org/A002392

 ///
 /// Returns std::numeric_limits<T>::digits on an input of 0.
 template <typename T> unsigned countLeadingZeros(T Val) {
   static_assert(std::is_unsigned_v<T>,
                 "Only unsigned integral types are allowed.");
   return llvm::countl_zero(Val);
 }
 
-/// Get the index of the first set bit starting from the least
-///   significant bit.
-///
-/// Only unsigned integral types are allowed.
-///
-/// \param ZB the behavior on an input of 0.
-template <typename T> T findFirstSet(T Val, ZeroBehavior ZB = ZB_Max) {
-  if (ZB == ZB_Max && Val == 0)
-    return std::numeric_limits<T>::max();
-
-  return llvm::countr_zero(Val);
-}
-
 /// 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) {
   static_assert(std::is_unsigned<T>::value, "Invalid type!");
   const unsigned Bits = CHAR_BIT * sizeof(T);
   assert(N <= Bits && "Invalid bit index");
   return N == 0 ? 0 : (T(-1) >> (Bits - 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) {
   return maskTrailingOnes<T>(CHAR_BIT * sizeof(T) - N);
 }
 
-/// Get the index of the last set bit starting from the least
-///   significant bit.
-///
-/// Only unsigned integral types are allowed.
-///
-/// \param ZB the behavior on an input of 0.
-template <typename T> T findLastSet(T Val, ZeroBehavior ZB = ZB_Max) {
-  if (ZB == ZB_Max && Val == 0)
-    return std::numeric_limits<T>::max();
-
-  // Use ^ instead of - because both gcc and llvm can remove the associated ^
-  // in the __builtin_clz intrinsic on x86.
-  return llvm::countl_zero(Val) ^ (std::numeric_limits<T>::digits - 1);
-}
-
 /// Macro compressed bit reversal table for 256 bits.
 ///
 /// http://graphics.stanford.edu/~seander/bithacks.html#BitReverseTable
 static const unsigned char BitReverseTable256[256] = {
 #define R2(n) n, n + 2 * 64, n + 1 * 64, n + 3 * 64
 #define R4(n) R2(n), R2(n + 2 * 16), R2(n + 1 * 16), R2(n + 3 * 16)
 #define R6(n) R4(n), R4(n + 2 * 4), R4(n + 1 * 4), R4(n + 3 * 4)
   R6(0), R6(2), R6(1), R6(3)

llvm/unittests/Support/MathExtrasTest.cpp

TEST(MathExtras, onesMask) {
   EXPECT_EQ(0xFFFFFFFFU, maskLeadingOnes<uint32_t>(32U));
   EXPECT_EQ(0xFFFFFFFFFFFFFFFFULL, maskTrailingOnes<uint64_t>(64U));
   EXPECT_EQ(0xFFFFFFFFFFFFFFFFULL, maskLeadingOnes<uint64_t>(64U));
 
   EXPECT_EQ(0x0000FFFFFFFFFFFFULL, maskTrailingOnes<uint64_t>(48U));
   EXPECT_EQ(0xFFFFFFFFFFFF0000ULL, maskLeadingOnes<uint64_t>(48U));
 }
 
-TEST(MathExtras, findFirstSet) {
-  uint8_t Z8 = 0;
-  uint16_t Z16 = 0;
-  uint32_t Z32 = 0;
-  uint64_t Z64 = 0;
-  EXPECT_EQ(0xFFULL, findFirstSet(Z8));
-  EXPECT_EQ(0xFFFFULL, findFirstSet(Z16));
-  EXPECT_EQ(0xFFFFFFFFULL, findFirstSet(Z32));
-  EXPECT_EQ(0xFFFFFFFFFFFFFFFFULL, findFirstSet(Z64));
-
-  uint8_t NZ8 = 42;
-  uint16_t NZ16 = 42;
-  uint32_t NZ32 = 42;
-  uint64_t NZ64 = 42;
-  EXPECT_EQ(1u, findFirstSet(NZ8));
-  EXPECT_EQ(1u, findFirstSet(NZ16));
-  EXPECT_EQ(1u, findFirstSet(NZ32));
-  EXPECT_EQ(1u, findFirstSet(NZ64));
-}
-
-TEST(MathExtras, findLastSet) {
-  uint8_t Z8 = 0;
-  uint16_t Z16 = 0;
-  uint32_t Z32 = 0;
-  uint64_t Z64 = 0;
-  EXPECT_EQ(0xFFULL, findLastSet(Z8));
-  EXPECT_EQ(0xFFFFULL, findLastSet(Z16));
-  EXPECT_EQ(0xFFFFFFFFULL, findLastSet(Z32));
-  EXPECT_EQ(0xFFFFFFFFFFFFFFFFULL, findLastSet(Z64));
-
-  uint8_t NZ8 = 42;
-  uint16_t NZ16 = 42;
-  uint32_t NZ32 = 42;
-  uint64_t NZ64 = 42;
-  EXPECT_EQ(5u, findLastSet(NZ8));
-  EXPECT_EQ(5u, findLastSet(NZ16));
-  EXPECT_EQ(5u, findLastSet(NZ32));
-  EXPECT_EQ(5u, findLastSet(NZ64));
-}
-
 TEST(MathExtras, isIntN) {
   EXPECT_TRUE(isIntN(16, 32767));
   EXPECT_FALSE(isIntN(16, 32768));
 }
 
 TEST(MathExtras, isUIntN) {
   EXPECT_TRUE(isUIntN(16, 65535));
   EXPECT_FALSE(isUIntN(16, 65536));