Fix off by one error in Bitfields

[courbet]

Can you add a unit test for this ?

[gchatelet]

In D83192#2135019, @courbet wrote:

Can you add a unit test for this ?

I'll add the following test as a separate commit if it LGTY.
Note: I can't use EXPECT_EQ because it takes the arguments by const & and the properties are static constexpr, the compiler complains about undefined reference.

TEST(BitfieldsTest, Properties) {
  using A = Bitfield::Element<bool, 0, 1>;
  EXPECT_TRUE(A::FirstBit == 0U);
  EXPECT_TRUE(A::LastBit == 0U);
  EXPECT_TRUE(A::Shift == 0U);
  EXPECT_TRUE(A::Bits == 1U);

  using B = Bitfield::Element<unsigned, 3, 4>;
  EXPECT_TRUE(B::FirstBit == 3U);
  EXPECT_TRUE(B::LastBit == 6U);
  EXPECT_TRUE(B::Shift == 3U);
  EXPECT_TRUE(B::Bits == 4U);
}

[courbet]

In D83192#2135079, @gchatelet wrote:

In D83192#2135019, @courbet wrote:

Can you add a unit test for this ?

I'll add the following test as a separate commit if it LGTY.
Note: I can't use EXPECT_EQ because it takes the arguments by const & and the properties are static constexpr, the compiler complains about undefined reference.

TEST(BitfieldsTest, Properties) {
  using A = Bitfield::Element<bool, 0, 1>;
  EXPECT_TRUE(A::FirstBit == 0U);
  EXPECT_TRUE(A::LastBit == 0U);
  EXPECT_TRUE(A::Shift == 0U);
  EXPECT_TRUE(A::Bits == 1U);

  using B = Bitfield::Element<unsigned, 3, 4>;
  EXPECT_TRUE(B::FirstBit == 3U);
  EXPECT_TRUE(B::LastBit == 6U);
  EXPECT_TRUE(B::Shift == 3U);
  EXPECT_TRUE(B::Bits == 4U);
}

SG

llvm/include/llvm/ADT/Bitfields.h

template <typename T, unsigned Offset, unsigned Size,
                              : std::numeric_limits<T>::max()>
   struct Element {
     using Type = T;
     using IntegerType =
         typename bitfields_details::ResolveUnderlyingType<T>::type;
     static constexpr unsigned Shift = Offset;
     static constexpr unsigned Bits = Size;
     static constexpr unsigned FirstBit = Offset;
-    static constexpr unsigned LastBit = Shift + Bits;
+    static constexpr unsigned LastBit = Shift + Bits - 1;
 
   private:
     template <typename, typename> friend struct bitfields_details::Impl;
 
     static_assert(Bits > 0, "Bits must be non zero");
     static constexpr size_t TypeBits = sizeof(IntegerType) * CHAR_BIT;
     static_assert(Bits <= TypeBits, "Bits may not be greater than T size");
     static_assert(!std::is_enum<T>::value || MaxValue != T(0),
struct Bitfield {
   template <typename Bitfield, typename StorageType>
   static void set(StorageType &Packed, typename Bitfield::Type Value) {
     using I = bitfields_details::Impl<Bitfield, StorageType>;
     I::update(Packed, static_cast<typename Bitfield::IntegerType>(Value));
   }
 
   /// Returns whether the two bitfields share common bits.
   template <typename A, typename B> static constexpr bool isOverlapping() {
-    return A::LastBit > B::FirstBit && B::LastBit > A::FirstBit;
+    return A::LastBit >= B::FirstBit && B::LastBit >= A::FirstBit;
   }
 };
 
 } // namespace llvm
 
 #endif // LLVM_ADT_BITFIELDS_H