Index: lib/CodeGen/MIRParser/MILexer.h
===================================================================
--- lib/CodeGen/MIRParser/MILexer.h
+++ lib/CodeGen/MIRParser/MILexer.h
@@ -94,26 +94,19 @@
 
 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) {}
+  MIToken() : Kind(Error) {}
 
-  MIToken(TokenKind Kind, StringRef Range, std::string StringValue,
-          unsigned StringOffset = 0)
-      : Kind(Kind), StringOffset(StringOffset), HasStringValue(true),
-        Range(Range), StringValue(std::move(StringValue)) {}
+  MIToken &reset(TokenKind Kind, StringRef Range);
 
-  MIToken(TokenKind Kind, StringRef Range, const APSInt &IntVal,
-          unsigned StringOffset = 0)
-      : Kind(Kind), StringOffset(StringOffset), HasStringValue(false),
-        Range(Range), IntVal(IntVal) {}
+  MIToken &setStringValue(StringRef StrVal);
+  MIToken &setOwnedStringValue(std::string StrVal);
+  MIToken &setIntegerValue(APSInt IntVal);
 
   TokenKind kind() const { return Kind; }
 
@@ -141,17 +134,10 @@
 
   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
@@ -55,6 +55,28 @@
 
 } // end anonymous namespace
 
+MIToken &MIToken::reset(TokenKind Kind, StringRef Range) {
+  this->Kind = Kind;
+  this->Range = Range;
+  return *this;
+}
+
+MIToken &MIToken::setStringValue(StringRef StrVal) {
+  StringValue = StrVal;
+  return *this;
+}
+
+MIToken &MIToken::setOwnedStringValue(std::string StrVal) {
+  StringValueStorage = std::move(StrVal);
+  StringValue = StringValueStorage;
+  return *this;
+}
+
+MIToken &MIToken::setIntegerValue(APSInt IntVal) {
+  this->IntVal = std::move(IntVal);
+  return *this;
+}
+
 /// Skip the leading whitespace characters and return the updated cursor.
 static Cursor skipWhitespace(Cursor C) {
   while (isspace(C.peek()))
@@ -124,17 +146,18 @@
   if (C.peek() == '"') {
     if (Cursor R = lexStringConstant(C, ErrorCallback)) {
       StringRef String = Range.upto(R);
-      Token = MIToken(Type, String,
-                      unescapeQuotedString(String.drop_front(PrefixLength)),
-                      PrefixLength);
+      Token.reset(Type, String)
+          .setOwnedStringValue(
+              unescapeQuotedString(String.drop_front(PrefixLength)));
       return R;
     }
-    Token = MIToken(MIToken::Error, Range.remaining());
+    Token.reset(MIToken::Error, Range.remaining());
     return Range;
   }
   while (isIdentifierChar(C.peek()))
     C.advance();
-  Token = MIToken(Type, Range.upto(C), PrefixLength);
+  Token.reset(Type, Range.upto(C))
+      .setStringValue(Range.upto(C).drop_front(PrefixLength));
   return C;
 }
 
@@ -145,7 +168,7 @@
   C.advance(); // Skip 'i'
   while (isdigit(C.peek()))
     C.advance();
-  Token = MIToken(MIToken::IntegerType, Range.upto(C));
+  Token.reset(MIToken::IntegerType, Range.upto(C));
   return C;
 }
 
@@ -187,7 +210,8 @@
   while (isIdentifierChar(C.peek()))
     C.advance();
   auto Identifier = Range.upto(C);
-  Token = MIToken(getIdentifierKind(Identifier), Identifier);
+  Token.reset(getIdentifierKind(Identifier), Identifier)
+      .setStringValue(Identifier);
   return C;
 }
 
@@ -199,7 +223,7 @@
   auto Range = C;
   C.advance(4); // Skip '%bb.'
   if (!isdigit(C.peek())) {
-    Token = MIToken(MIToken::Error, C.remaining());
+    Token.reset(MIToken::Error, C.remaining());
     ErrorCallback(C.location(), "expected a number after '%bb.'");
     return C;
   }
@@ -214,8 +238,9 @@
     while (isIdentifierChar(C.peek()))
       C.advance();
   }
-  Token = MIToken(MIToken::MachineBasicBlock, Range.upto(C), APSInt(Number),
-                  StringOffset);
+  Token.reset(MIToken::MachineBasicBlock, Range.upto(C))
+      .setIntegerValue(APSInt(Number))
+      .setStringValue(Range.upto(C).drop_front(StringOffset));
   return C;
 }
 
@@ -228,7 +253,7 @@
   auto NumberRange = C;
   while (isdigit(C.peek()))
     C.advance();
-  Token = MIToken(Kind, Range.upto(C), APSInt(NumberRange.upto(C)));
+  Token.reset(Kind, Range.upto(C)).setIntegerValue(APSInt(NumberRange.upto(C)));
   return C;
 }
 
@@ -249,7 +274,9 @@
     while (isIdentifierChar(C.peek()))
       C.advance();
   }
-  Token = MIToken(Kind, Range.upto(C), APSInt(Number), StringOffset);
+  Token.reset(Kind, Range.upto(C))
+      .setIntegerValue(APSInt(Number))
+      .setStringValue(Range.upto(C).drop_front(StringOffset));
   return C;
 }
 
@@ -295,8 +322,8 @@
   auto NumberRange = C;
   while (isdigit(C.peek()))
     C.advance();
-  Token = MIToken(MIToken::VirtualRegister, Range.upto(C),
-                  APSInt(NumberRange.upto(C)));
+  Token.reset(MIToken::VirtualRegister, Range.upto(C))
+      .setIntegerValue(APSInt(NumberRange.upto(C)));
   return C;
 }
 
@@ -309,8 +336,8 @@
   C.advance(); // Skip '%'
   while (isIdentifierChar(C.peek()))
     C.advance();
-  Token = MIToken(MIToken::NamedRegister, Range.upto(C),
-                  /*StringOffset=*/1); // Drop the '%'
+  Token.reset(MIToken::NamedRegister, Range.upto(C))
+      .setStringValue(Range.upto(C).drop_front(1)); // Drop the '%'
   return C;
 }
 
@@ -327,8 +354,8 @@
   auto NumberRange = C;
   while (isdigit(C.peek()))
     C.advance();
-  Token =
-      MIToken(MIToken::GlobalValue, Range.upto(C), APSInt(NumberRange.upto(C)));
+  Token.reset(MIToken::GlobalValue, Range.upto(C))
+      .setIntegerValue(APSInt(NumberRange.upto(C)));
   return C;
 }
 
@@ -354,7 +381,7 @@
     C.advance();
   while (isxdigit(C.peek()))
     C.advance();
-  Token = MIToken(MIToken::FloatingPointLiteral, Range.upto(C));
+  Token.reset(MIToken::FloatingPointLiteral, Range.upto(C));
   return C;
 }
 
@@ -370,7 +397,7 @@
     while (isdigit(C.peek()))
       C.advance();
   }
-  Token = MIToken(MIToken::FloatingPointLiteral, Range.upto(C));
+  Token.reset(MIToken::FloatingPointLiteral, Range.upto(C));
   return C;
 }
 
@@ -384,7 +411,7 @@
   if (C.peek() == '.')
     return lexFloatingPointLiteral(Range, C, Token);
   StringRef StrVal = Range.upto(C);
-  Token = MIToken(MIToken::IntegerLiteral, StrVal, APSInt(StrVal));
+  Token.reset(MIToken::IntegerLiteral, StrVal).setIntegerValue(APSInt(StrVal));
   return C;
 }
 
@@ -423,7 +450,7 @@
     return None;
   auto Range = C;
   C.advance(Length);
-  Token = MIToken(Kind, Range.upto(C));
+  Token.reset(Kind, Range.upto(C));
   return C;
 }
 
@@ -432,7 +459,7 @@
     function_ref<void(StringRef::iterator Loc, const Twine &)> ErrorCallback) {
   auto C = skipWhitespace(Cursor(Source));
   if (C.isEOF()) {
-    Token = MIToken(MIToken::Eof, C.remaining());
+    Token.reset(MIToken::Eof, C.remaining());
     return C.remaining();
   }
 
@@ -467,7 +494,7 @@
   if (Cursor R = maybeLexSymbol(C, Token))
     return R.remaining();
 
-  Token = MIToken(MIToken::Error, C.remaining());
+  Token.reset(MIToken::Error, C.remaining());
   ErrorCallback(C.location(),
                 Twine("unexpected character '") + Twine(C.peek()) + "'");
   return C.remaining();
Index: lib/CodeGen/MIRParser/MIParser.cpp
===================================================================
--- lib/CodeGen/MIRParser/MIParser.cpp
+++ lib/CodeGen/MIRParser/MIParser.cpp
@@ -200,7 +200,7 @@
                    StringRef Source, const PerFunctionMIParsingState &PFS,
                    const SlotMapping &IRSlots)
     : SM(SM), MF(MF), Error(Error), Source(Source), CurrentSource(Source),
-      Token(MIToken::Error, StringRef()), PFS(PFS), IRSlots(IRSlots) {}
+      PFS(PFS), IRSlots(IRSlots) {}
 
 void MIParser::lex() {
   CurrentSource = lexMIToken(
@@ -571,7 +571,7 @@
 }
 
 bool MIParser::parseIRConstant(StringRef::iterator Loc, const Constant *&C) {
-  auto Source = StringRef(Loc, Token.stringValue().end() - Loc).str();
+  auto Source = StringRef(Loc, Token.range().end() - Loc).str();
   lex();
   SMDiagnostic Err;
   C = parseConstantValue(Source.c_str(), Err, *MF.getFunction()->getParent());
@@ -681,8 +681,8 @@
     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: {
@@ -851,8 +851,7 @@
     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: {
@@ -1019,7 +1018,7 @@
 bool MIParser::parseOperandsOffset(MachineOperand &Op) {
   if (Token.isNot(MIToken::plus) && Token.isNot(MIToken::minus))
     return false;
-  StringRef Sign = Token.stringValue();
+  StringRef Sign = Token.range();
   bool IsNegative = Token.is(MIToken::minus);
   lex();
   if (Token.isNot(MIToken::IntegerLiteral))
@@ -1039,8 +1038,7 @@
   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.