MIR Serialization: Serialize the null register operands.

This commit serializes the null register machine operands.
It uses the '_' keyword to represent them, but the parser
also allows the '%noreg' named register syntax.

Reviewers: Duncan P. N. Exon Smith

Differential Revision: http://reviews.llvm.org/D10580


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240558 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/MIRParser/MILexer.cpp

@@ -64,7 +64,9 @@ static Cursor lexIdentifier(Cursor C, MIToken &Token) {
   auto Range = C;
   while (isIdentifierChar(C.peek()))
     C.advance();
-  Token = MIToken(MIToken::Identifier, Range.upto(C));
+  auto Identifier = Range.upto(C);
+  Token = MIToken(Identifier == "_" ? MIToken::underscore : MIToken::Identifier,
+                  Identifier);
   return C;
 }