4 files changed, 16 insertions, 4 deletions
diff --git a/llvm/lib/CodeGen/MIRParser/MILexer.cpp b/llvm/lib/CodeGen/MIRParser/MILexer.cpp
index 0933ae138f2..3383d1f5cf5 100644
--- a/llvm/lib/CodeGen/MIRParser/MILexer.cpp
+++ b/llvm/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;
 }
 
diff --git a/llvm/lib/CodeGen/MIRParser/MILexer.h b/llvm/lib/CodeGen/MIRParser/MILexer.h
index df8b6cb2026..f9cc97cb34e 100644
--- a/llvm/lib/CodeGen/MIRParser/MILexer.h
+++ b/llvm/lib/CodeGen/MIRParser/MILexer.h
@@ -34,6 +34,7 @@ struct MIToken {
     // Tokens with no info.
     comma,
     equal,
+    underscore,
 
     // Identifier tokens
     Identifier,
@@ -58,7 +59,9 @@ public:
 
   bool isError() const { return Kind == Error; }
 
-  bool isRegister() const { return Kind == NamedRegister; }
+  bool isRegister() const {
+    return Kind == NamedRegister || Kind == underscore;
+  }
 
   bool is(TokenKind K) const { return Kind == K; }
 
diff --git a/llvm/lib/CodeGen/MIRParser/MIParser.cpp b/llvm/lib/CodeGen/MIRParser/MIParser.cpp
index 33f306945cb..07aac674ffb 100644
--- a/llvm/lib/CodeGen/MIRParser/MIParser.cpp
+++ b/llvm/lib/CodeGen/MIRParser/MIParser.cpp
@@ -174,6 +174,9 @@ bool MIParser::parseInstruction(unsigned &OpCode) {
 
 bool MIParser::parseRegister(unsigned &Reg) {
   switch (Token.kind()) {
+  case MIToken::underscore:
+    Reg = 0;
+    break;
   case MIToken::NamedRegister: {
     StringRef Name = Token.stringValue().drop_front(1); // Drop the '%'
     if (getRegisterByName(Name, Reg))
@@ -211,6 +214,7 @@ bool MIParser::parseImmediateOperand(MachineOperand &Dest) {
 
 bool MIParser::parseMachineOperand(MachineOperand &Dest) {
   switch (Token.kind()) {
+  case MIToken::underscore:
   case MIToken::NamedRegister:
     return parseRegisterOperand(Dest);
   case MIToken::IntegerLiteral:
@@ -245,6 +249,8 @@ bool MIParser::parseInstrName(StringRef InstrName, unsigned &OpCode) {
 void MIParser::initNames2Regs() {
   if (!Names2Regs.empty())
     return;
+  // The '%noreg' register is the register 0.
+  Names2Regs.insert(std::make_pair("noreg", 0));
   const auto *TRI = MF.getSubtarget().getRegisterInfo();
   assert(TRI && "Expected target register info");
   for (unsigned I = 0, E = TRI->getNumRegs(); I < E; ++I) {
diff --git a/llvm/lib/CodeGen/MIRPrinter.cpp b/llvm/lib/CodeGen/MIRPrinter.cpp
index 6d62b0ad85b..801f6c25ac5 100644
--- a/llvm/lib/CodeGen/MIRPrinter.cpp
+++ b/llvm/lib/CodeGen/MIRPrinter.cpp
@@ -144,9 +144,10 @@ void MIPrinter::print(const MachineInstr &MI) {
 static void printReg(unsigned Reg, raw_ostream &OS,
                      const TargetRegisterInfo *TRI) {
   // TODO: Print Stack Slots.
-  // TODO: Print no register.
   // TODO: Print virtual registers.
-  if (Reg < TRI->getNumRegs())
+  if (!Reg)
+    OS << '_';
+  else if (Reg < TRI->getNumRegs())
     OS << '%' << StringRef(TRI->getName(Reg)).lower();
   else
     llvm_unreachable("Can't print this kind of register yet");