Index: lib/CodeGen/MIRParser/MILexer.h
===================================================================
--- lib/CodeGen/MIRParser/MILexer.h
+++ lib/CodeGen/MIRParser/MILexer.h
@@ -91,26 +91,38 @@
 
 private:
   TokenKind Kind;
-  unsigned StringOffset;
-  bool HasStringValue;
   StringRef Range;
-  std::string StringValue;
+  StringRef StringValue;
+  std::string StringValueStorage;
   APSInt IntVal;
 
 public:
   MIToken(TokenKind Kind, StringRef Range, unsigned StringOffset = 0)
-      : Kind(Kind), StringOffset(StringOffset), HasStringValue(false),
-        Range(Range) {}
+      : Kind(Kind), Range(Range), StringValue(Range.drop_front(StringOffset)) {}
 
-  MIToken(TokenKind Kind, StringRef Range, std::string StringValue,
-          unsigned StringOffset = 0)
-      : Kind(Kind), StringOffset(StringOffset), HasStringValue(true),
-        Range(Range), StringValue(std::move(StringValue)) {}
+  MIToken(TokenKind Kind, StringRef Range, std::string StrVal)
+      : Kind(Kind), Range(Range), StringValueStorage(std::move(StrVal)) {
+    StringValue = StringValueStorage;
+  }
 
   MIToken(TokenKind Kind, StringRef Range, const APSInt &IntVal,
           unsigned StringOffset = 0)
-      : Kind(Kind), StringOffset(StringOffset), HasStringValue(false),
-        Range(Range), IntVal(IntVal) {}
+      : Kind(Kind), Range(Range), StringValue(Range.drop_front(StringOffset)),
+        IntVal(IntVal) {}
+
+  MIToken &operator=(MIToken &&Other) {
+    Kind = Other.Kind;
+    Range = std::move(Other.Range);
+    StringValueStorage = std::move(Other.StringValueStorage);
+    if (StringValueStorage.empty())
+      StringValue = std::move(Other.StringValue);
+    else {
+      StringValue = StringValueStorage;
+      Other.StringValue = "";
+    }
+    IntVal = std::move(Other.IntVal);
+    return *this;
+  }
 
   TokenKind kind() const { return Kind; }
 
@@ -135,17 +147,10 @@
 
   StringRef::iterator location() const { return Range.begin(); }
 
-  /// Return the token's raw string value.
-  ///
-  /// If the string value is quoted, this method returns that quoted string as
-  /// it is, without unescaping the string value.
-  StringRef rawStringValue() const { return Range.drop_front(StringOffset); }
+  StringRef range() const { return Range; }
 
   /// Return the token's string value.
-  StringRef stringValue() const {
-    return HasStringValue ? StringRef(StringValue)
-                          : Range.drop_front(StringOffset);
-  }
+  StringRef stringValue() const { return StringValue; }
 
   const APSInt &integerValue() const { return IntVal; }
 
Index: lib/CodeGen/MIRParser/MILexer.cpp
===================================================================
--- lib/CodeGen/MIRParser/MILexer.cpp
+++ lib/CodeGen/MIRParser/MILexer.cpp
@@ -125,8 +125,7 @@
     if (Cursor R = lexStringConstant(C, ErrorCallback)) {
       StringRef String = Range.upto(R);
       Token = MIToken(Type, String,
-                      unescapeQuotedString(String.drop_front(PrefixLength)),
-                      PrefixLength);
+                      unescapeQuotedString(String.drop_front(PrefixLength)));
       return R;
     }
     Token = MIToken(MIToken::Error, Range.remaining());
Index: lib/CodeGen/MIRParser/MIParser.cpp
===================================================================
--- lib/CodeGen/MIRParser/MIParser.cpp
+++ lib/CodeGen/MIRParser/MIParser.cpp
@@ -670,8 +670,8 @@
     const Module *M = MF.getFunction()->getParent();
     GV = M->getNamedValue(Token.stringValue());
     if (!GV)
-      return error(Twine("use of undefined global value '@") +
-                   Token.rawStringValue() + "'");
+      return error(Twine("use of undefined global value '") + Token.range() +
+                   "'");
     break;
   }
   case MIToken::GlobalValue: {
@@ -844,8 +844,7 @@
     BB = dyn_cast_or_null<BasicBlock>(
         F.getValueSymbolTable().lookup(Token.stringValue()));
     if (!BB)
-      return error(Twine("use of undefined IR block '%ir-block.") +
-                   Token.rawStringValue() + "'");
+      return error(Twine("use of undefined IR block '") + Token.range() + "'");
     break;
   }
   case MIToken::IRBlock: {
@@ -1005,8 +1004,7 @@
   case MIToken::NamedIRValue: {
     V = MF.getFunction()->getValueSymbolTable().lookup(Token.stringValue());
     if (!V)
-      return error(Twine("use of undefined IR value '%ir.") +
-                   Token.rawStringValue() + "'");
+      return error(Twine("use of undefined IR value '") + Token.range() + "'");
     break;
   }
   // TODO: Parse unnamed IR value references.