[llvm] [IR] Add initial support for the byte type (PR #178666)

[Nikita Popov via llvm-commits]

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@@ -100,6 +100,59 @@ unsigned Type::getIntegerBitWidth() const {
   return cast<IntegerType>(this)->getBitWidth();
 }
 
+/// Class to represent byte types.
+class ByteType : public Type {
+  friend class LLVMContextImpl;
+
+protected:
+  explicit ByteType(LLVMContext &C, unsigned NumBits) : Type(C, ByteTyID) {
+    setSubclassData(NumBits);
+  }
+
+public:
+  /// This enum is just used to hold constants we need for ByteType.
+  enum {
+    MIN_BYTE_BITS = 1, ///< Minimum number of bits that can be specified
+    MAX_BYTE_BITS =
+        (1 << 23) ///< Maximum number of bits that can be specified
+                  ///< Note that bit width is stored in the Type classes
+                  ///< SubclassData field which has 24 bits. SelectionDAG type
+                  ///< legalization can require a power of 2 ByteType, so limit
+                  ///< to the largest representable power of 2, 8388608.
+  };
+
+  /// This static method is the primary way of constructing a ByteType.
+  /// If a ByteType with the same NumBits value was previously instantiated,
+  /// that instance will be returned. Otherwise a new one will be created. Only
+  /// one instance with a given NumBits value is ever created.
+  /// Get or create a ByteType instance.
+  LLVM_ABI static ByteType *get(LLVMContext &C, unsigned NumBits);
+
+  /// Returns type twice as wide the input type.
+  ByteType *getExtendedType() const {
+    return Type::getByteNTy(getContext(), 2 * getScalarSizeInBits());
+  }
+
+  /// Get the number of bits in this ByteType
+  unsigned getBitWidth() const { return getSubclassData(); }
+
+  /// Return a bitmask with ones set for all of the bits. This is 0xFF for i8,
+  /// 0xFFFF for i16, etc.
+  uint64_t getBitMask() const { return ~uint64_t(0UL) >> (64 - getBitWidth()); }
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nikic wrote:

I'd omit this unless/until we find it is useful.

getExtendedType() also looks kind of dubious in this context.

https://github.com/llvm/llvm-project/pull/178666