Index: lib/Target/X86/Disassembler/X86Disassembler.cpp
===================================================================
--- lib/Target/X86/Disassembler/X86Disassembler.cpp
+++ lib/Target/X86/Disassembler/X86Disassembler.cpp
@@ -96,25 +96,17 @@
   }
 }
 
-struct Region {
-  ArrayRef<uint8_t> Bytes;
-  uint64_t Base;
-  Region(ArrayRef<uint8_t> Bytes, uint64_t Base) : Bytes(Bytes), Base(Base) {}
-};
-
-/// A callback function that wraps the readByte method from Region.
+/// A callback function that wraps the readByte method from an ArrayRef<uint8_t>
 ///
 /// @param Arg      - The generic callback parameter.  In this case, this should
-///                   be a pointer to a Region.
+///                   be a pointer to a ArrayRef<uint8_t>.
 /// @param Byte     - A pointer to the byte to be read.
 /// @param Address  - The address to be read.
 static int regionReader(const void *Arg, uint8_t *Byte, uint64_t Address) {
-  auto *R = static_cast<const Region *>(Arg);
-  ArrayRef<uint8_t> Bytes = R->Bytes;
-  unsigned Index = Address - R->Base;
-  if (Bytes.size() <= Index)
+  const ArrayRef<uint8_t> *Bytes = static_cast<const ArrayRef<uint8_t> *>(Arg);
+  if (Bytes->size() <= Address)
     return -1;
-  *Byte = Bytes[Index];
+  *Byte = Bytes->data()[Address];
   return 0;
 }
 
@@ -147,9 +139,7 @@
   if (&VStream == &nulls())
     LoggerFn = nullptr; // Disable logging completely if it's going to nulls().
 
-  Region R(Bytes, Address);
-
-  int Ret = decodeInstruction(&InternalInstr, regionReader, (const void *)&R,
+  int Ret = decodeInstruction(&InternalInstr, regionReader, (const void *)&Bytes,
                               LoggerFn, (void *)&VStream,
                               (const void *)MII.get(), Address, fMode);