Mips assembler: Enable handling of nested expressions

This patch allows the Mips assembler to parse and emit nested 
expressions as instruction operands. It also extends the 
expansion of memory instructions when an offset is given as 
an expression. 

Contributer: Vladimir Medic



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179657 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 263 insertions, 133 deletions

diff --git a/lib/Target/Mips/AsmParser/MipsAsmParser.cpp b/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
index e8319f100f9..d06877f9453 100644
--- a/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
+++ b/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
@@ -127,9 +127,12 @@ class MipsAsmParser : public MCTargetAsmParser {
                      bool isLoad,bool isImmOpnd);
   bool reportParseError(StringRef ErrorMsg);
 
-  bool parseMemOffset(const MCExpr *&Res);
+  bool parseMemOffset(const MCExpr *&Res, bool isParenExpr);
   bool parseRelocOperand(const MCExpr *&Res);
 
+  const MCExpr* evaluateRelocExpr(const MCExpr *Expr, StringRef RelocStr);
+
+  bool isEvaluated(const MCExpr *Expr);
   bool parseDirectiveSet();
 
   bool parseSetAtDirective();
@@ -409,7 +412,7 @@ static const MCInstrDesc &getInstDesc(unsigned Opcode) {
 }
 
 bool MipsAsmParser::processInstruction(MCInst &Inst, SMLoc IDLoc,
-                        SmallVectorImpl<MCInst> &Instructions) {
+                                       SmallVectorImpl<MCInst> &Instructions) {
   const MCInstrDesc &MCID = getInstDesc(Inst.getOpcode());
   Inst.setLoc(IDLoc);
   if (MCID.mayLoad() || MCID.mayStore()) {
@@ -431,17 +434,20 @@ bool MipsAsmParser::processInstruction(MCInst &Inst, SMLoc IDLoc,
           const MCExpr *Expr = Op.getExpr();
           if (Expr->getKind() == MCExpr::SymbolRef){
             const MCSymbolRefExpr *SR =
-                    static_cast<const MCSymbolRefExpr*>(Expr);
+                static_cast<const MCSymbolRefExpr*>(Expr);
             if (SR->getKind() == MCSymbolRefExpr::VK_None) {
               // Expand symbol
               expandMemInst(Inst,IDLoc,Instructions,MCID.mayLoad(),false);
               return false;
             }
+          } else if (!isEvaluated(Expr)) {
+            expandMemInst(Inst,IDLoc,Instructions,MCID.mayLoad(),false);
+            return false;
           }
         }
       }
-    }
-  }
+    }// For
+  }// If load/store
 
   if (needsExpansion(Inst))
     expandInstruction(Inst, IDLoc, Instructions);
@@ -644,20 +650,23 @@ void MipsAsmParser::expandMemInst(MCInst &Inst, SMLoc IDLoc,
                                         MCSymbolRefExpr::VK_Mips_ABS_HI,
                                         getContext());
       TempInst.addOperand(MCOperand::CreateExpr(HiExpr));
+    } else {
+      const MCExpr *HiExpr = evaluateRelocExpr(ExprOffset,"hi");
+      TempInst.addOperand(MCOperand::CreateExpr(HiExpr));
     }
   }
   // Add the instruction to the list
   Instructions.push_back(TempInst);
-  // and prepare TempInst for next instruction
+  // And prepare TempInst for next instruction
   TempInst.clear();
-  // which is add temp register to base
+  // Which is add temp register to base
   TempInst.setOpcode(Mips::ADDu);
   TempInst.addOperand(MCOperand::CreateReg(TmpRegNum));
   TempInst.addOperand(MCOperand::CreateReg(TmpRegNum));
   TempInst.addOperand(MCOperand::CreateReg(BaseRegNum));
   Instructions.push_back(TempInst);
   TempInst.clear();
-  // and finaly, create original instruction with low part
+  // And finaly, create original instruction with low part
   // of offset and new base
   TempInst.setOpcode(Inst.getOpcode());
   TempInst.addOperand(MCOperand::CreateReg(RegOpNum));
@@ -671,6 +680,9 @@ void MipsAsmParser::expandMemInst(MCInst &Inst, SMLoc IDLoc,
                                       MCSymbolRefExpr::VK_Mips_ABS_LO,
                                       getContext());
       TempInst.addOperand(MCOperand::CreateExpr(LoExpr));
+    } else {
+      const MCExpr *LoExpr = evaluateRelocExpr(ExprOffset,"lo");
+      TempInst.addOperand(MCOperand::CreateExpr(LoExpr));
     }
   }
   Instructions.push_back(TempInst);
@@ -960,13 +972,13 @@ bool MipsAsmParser::ParseOperand(SmallVectorImpl<MCParsedAsmOperand*>&Operands,
     // we need to assigne the propper RegisterKind
    if (searchSymbolAlias(Operands,MipsOperand::Kind_None))
      return false;
-    //else drop to expression parsing
+    // Else drop to expression parsing
   case AsmToken::LParen:
   case AsmToken::Minus:
   case AsmToken::Plus:
   case AsmToken::Integer:
   case AsmToken::String: {
-     // quoted label names
+     // Quoted label names
     const MCExpr *IdVal;
     SMLoc S = Parser.getTok().getLoc();
     if (getParser().parseExpression(IdVal))
@@ -976,9 +988,9 @@ bool MipsAsmParser::ParseOperand(SmallVectorImpl<MCParsedAsmOperand*>&Operands,
     return false;
   }
   case AsmToken::Percent: {
-    // it is a symbol reference or constant expression
+    // It is a symbol reference or constant expression
     const MCExpr *IdVal;
-    SMLoc S = Parser.getTok().getLoc(); // start location of the operand
+    SMLoc S = Parser.getTok().getLoc(); // Start location of the operand
     if (parseRelocOperand(IdVal))
       return true;
 
@@ -991,31 +1003,100 @@ bool MipsAsmParser::ParseOperand(SmallVectorImpl<MCParsedAsmOperand*>&Operands,
   return true;
 }
 
+const MCExpr* MipsAsmParser::evaluateRelocExpr(const MCExpr *Expr,
+                                               StringRef RelocStr) {
+
+  const MCExpr *Res;
+  // Check the type of the expression
+  if (const MCConstantExpr *MCE = dyn_cast<MCConstantExpr>(Expr)) {
+    // It's a constant, evaluate lo or hi value
+    if (RelocStr == "lo") {
+      short Val = MCE->getValue();
+      Res = MCConstantExpr::Create(Val, getContext());
+    } else if (RelocStr == "hi") {
+      int Val = MCE->getValue();
+      int LoSign = Val & 0x8000;
+      Val = (Val & 0xffff0000) >> 16;
+      // Lower part is treated as a signed int, so if it is negative
+      // we must add 1 to the hi part to compensate
+      if (LoSign)
+        Val++;
+      Res = MCConstantExpr::Create(Val, getContext());
+    }
+   return Res;
+  }
+
+  if (const MCSymbolRefExpr *MSRE = dyn_cast<MCSymbolRefExpr>(Expr)) {
+    // It's a symbol, create symbolic expression from symbol
+    StringRef Symbol = MSRE->getSymbol().getName();
+    MCSymbolRefExpr::VariantKind VK = getVariantKind(RelocStr);
+    Res = MCSymbolRefExpr::Create(Symbol,VK,getContext());
+    return Res;
+  }
+
+  if (const MCBinaryExpr *BE = dyn_cast<MCBinaryExpr>(Expr)) {
+    const MCExpr *LExp = evaluateRelocExpr(BE->getLHS(),RelocStr);
+    const MCExpr *RExp = evaluateRelocExpr(BE->getRHS(),RelocStr);
+    Res = MCBinaryExpr::Create(BE->getOpcode(), LExp, RExp, getContext());
+    return Res;
+  }
+
+  if (const MCUnaryExpr *UN = dyn_cast<MCUnaryExpr>(Expr)) {
+    const MCExpr *UnExp = evaluateRelocExpr(UN->getSubExpr(),RelocStr);
+  Res = MCUnaryExpr::Create(UN->getOpcode(), UnExp, getContext());
+  return Res;
+  }
+  // Just return the original expr
+  return Expr;
+}
+
+bool MipsAsmParser::isEvaluated(const MCExpr *Expr) {
+
+  switch (Expr->getKind()) {
+  case MCExpr::Constant:
+    return true;
+  case MCExpr::SymbolRef:
+    return (cast<MCSymbolRefExpr>(Expr)->getKind() != MCSymbolRefExpr::VK_None);
+  case MCExpr::Binary:
+    if (const MCBinaryExpr *BE = dyn_cast<MCBinaryExpr>(Expr)) {
+      if (!isEvaluated(BE->getLHS()))
+        return false;
+      return isEvaluated(BE->getRHS());
+    }
+  case MCExpr::Unary:
+    return isEvaluated(cast<MCUnaryExpr>(Expr)->getSubExpr());
+  default:
+    return false;
+  }
+  return false;
+
+}
 bool MipsAsmParser::parseRelocOperand(const MCExpr *&Res) {
 
-  Parser.Lex(); // eat % token
-  const AsmToken &Tok = Parser.getTok(); // get next token, operation
+
+  Parser.Lex(); // Eat % token
+  const AsmToken &Tok = Parser.getTok(); // Get next token, operation
   if (Tok.isNot(AsmToken::Identifier))
     return true;
 
   std::string Str = Tok.getIdentifier().str();
 
-  Parser.Lex(); // eat identifier
-  // now make expression from the rest of the operand
+  Parser.Lex(); // Eat identifier
+  // Now make expression from the rest of the operand
   const MCExpr *IdVal;
   SMLoc EndLoc;
 
   if (getLexer().getKind() == AsmToken::LParen) {
     while (1) {
-      Parser.Lex(); // eat '(' token
+      Parser.Lex(); // Eat '(' token
       if (getLexer().getKind() == AsmToken::Percent) {
-        Parser.Lex(); // eat % token
+        Parser.Lex(); // Eat % token
         const AsmToken &nextTok = Parser.getTok();
         if (nextTok.isNot(AsmToken::Identifier))
           return true;
         Str += "(%";
         Str += nextTok.getIdentifier();
-        Parser.Lex(); // eat identifier
+        Parser.Lex(); // Eat identifier
         if (getLexer().getKind() != AsmToken::LParen)
           return true;
       } else
@@ -1025,38 +1106,13 @@ bool MipsAsmParser::parseRelocOperand(const MCExpr *&Res) {
       return true;
 
     while (getLexer().getKind() == AsmToken::RParen)
-      Parser.Lex(); // eat ')' token
+      Parser.Lex(); // Eat ')' token
 
   } else
-    return true; // parenthesis must follow reloc operand
+    return true; // Parenthesis must follow reloc operand
 
-  // Check the type of the expression
-  if (const MCConstantExpr *MCE = dyn_cast<MCConstantExpr>(IdVal)) {
-    // It's a constant, evaluate lo or hi value
-    if (Str == "lo") {
-      short Val = MCE->getValue();
-      Res = MCConstantExpr::Create(Val, getContext());
-    } else if (Str == "hi") {
-      int Val = MCE->getValue();
-      int LoSign = Val & 0x8000;
-      Val = (Val & 0xffff0000) >> 16;
-      // Lower part is treated as a signed int, so if it is negative
-      // we must add 1 to the hi part to compensate
-      if (LoSign)
-        Val++;
-      Res = MCConstantExpr::Create(Val, getContext());
-    }
-    return false;
-  }
-
-  if (const MCSymbolRefExpr *MSRE = dyn_cast<MCSymbolRefExpr>(IdVal)) {
-    // It's a symbol, create symbolic expression from symbol
-    StringRef Symbol = MSRE->getSymbol().getName();
-    MCSymbolRefExpr::VariantKind VK = getVariantKind(Str);
-    Res = MCSymbolRefExpr::Create(Symbol,VK,getContext());
-    return false;
-  }
-  return true;
+  Res = evaluateRelocExpr(IdVal,Str);
+  return false;
 }
 
 bool MipsAsmParser::ParseRegister(unsigned &RegNo, SMLoc &StartLoc,
@@ -1068,24 +1124,33 @@ bool MipsAsmParser::ParseRegister(unsigned &RegNo, SMLoc &StartLoc,
   return (RegNo == (unsigned)-1);
 }
 
-bool MipsAsmParser::parseMemOffset(const MCExpr *&Res) {
+bool MipsAsmParser::parseMemOffset(const MCExpr *&Res, bool isParenExpr) {
 
   SMLoc S;
+  bool Result = true;
+
+  while (getLexer().getKind() == AsmToken::LParen)
+    Parser.Lex();
 
   switch(getLexer().getKind()) {
   default:
     return true;
   case AsmToken::Identifier:
+  case AsmToken::LParen:
   case AsmToken::Integer:
   case AsmToken::Minus:
   case AsmToken::Plus:
-    return (getParser().parseExpression(Res));
+    if (isParenExpr)
+      Result =  getParser().parseParenExpression(Res,S);
+    else
+      Result = (getParser().parseExpression(Res));
+  while (getLexer().getKind() == AsmToken::RParen)
+      Parser.Lex();
+   break;
   case AsmToken::Percent:
-    return parseRelocOperand(Res);
-  case AsmToken::LParen:
-    return false;  // it's probably assuming 0
+    Result = parseRelocOperand(Res);
   }
-  return true;
+  return Result;
 }
 
 MipsAsmParser::OperandMatchResultTy MipsAsmParser::parseMemOperand(
@@ -1093,27 +1158,46 @@ MipsAsmParser::OperandMatchResultTy MipsAsmParser::parseMemOperand(
 
   const MCExpr *IdVal = 0;
   SMLoc S;
-  // first operand is the offset
+  bool isParenExpr = false;
+  // First operand is the offset
   S = Parser.getTok().getLoc();
 
-  if (parseMemOffset(IdVal))
-    return MatchOperand_ParseFail;
+  if (getLexer().getKind() == AsmToken::LParen) {
+    Parser.Lex();
+    isParenExpr = true;
+  }
 
-  const AsmToken &Tok = Parser.getTok(); // get next token
-  if (Tok.isNot(AsmToken::LParen)) {
-    MipsOperand *Mnemonic = static_cast<MipsOperand*>(Operands[0]);
-    if (Mnemonic->getToken() == "la") {
-      SMLoc E = SMLoc::getFromPointer(Parser.getTok().getLoc().getPointer() -1);
-      Operands.push_back(MipsOperand::CreateImm(IdVal, S, E));
-      return MatchOperand_Success;
+  if (getLexer().getKind() != AsmToken::Dollar) {
+    if (parseMemOffset(IdVal,isParenExpr))
+      return MatchOperand_ParseFail;
+
+    const AsmToken &Tok = Parser.getTok(); // Get next token
+    if (Tok.isNot(AsmToken::LParen)) {
+      MipsOperand *Mnemonic = static_cast<MipsOperand*>(Operands[0]);
+      if (Mnemonic->getToken() == "la") {
+        SMLoc E = SMLoc::getFromPointer(
+            Parser.getTok().getLoc().getPointer() -1);
+        Operands.push_back(MipsOperand::CreateImm(IdVal, S, E));
+        return MatchOperand_Success;
+      }
+      if (Tok.is(AsmToken::EndOfStatement)) {
+        SMLoc E = SMLoc::getFromPointer(
+            Parser.getTok().getLoc().getPointer() -1);
+
+        // Zero register assumed, add memory operand with ZERO as base
+        Operands.push_back(MipsOperand::CreateMem(isMips64()?
+                                                  Mips::ZERO_64:Mips::ZERO,
+                                                  IdVal, S, E));
+        return MatchOperand_Success;
+      }
+      Error(Parser.getTok().getLoc(), "'(' expected");
+      return MatchOperand_ParseFail;
     }
-    Error(Parser.getTok().getLoc(), "'(' expected");
-    return MatchOperand_ParseFail;
-  }
 
-  Parser.Lex(); // Eat '(' token.
+    Parser.Lex(); // Eat '(' token.
+  }
 
-  const AsmToken &Tok1 = Parser.getTok(); // get next token
+  const AsmToken &Tok1 = Parser.getTok(); // Get next token
   if (Tok1.is(AsmToken::Dollar)) {
     Parser.Lex(); // Eat '$' token.
     if (tryParseRegisterOperand(Operands, isMips64())) {
@@ -1126,7 +1210,7 @@ MipsAsmParser::OperandMatchResultTy MipsAsmParser::parseMemOperand(
     return MatchOperand_ParseFail;
   }
 
-  const AsmToken &Tok2 = Parser.getTok(); // get next token
+  const AsmToken &Tok2 = Parser.getTok(); // Get next token
   if (Tok2.isNot(AsmToken::RParen)) {
     Error(Parser.getTok().getLoc(), "')' expected");
     return MatchOperand_ParseFail;
@@ -1139,12 +1223,21 @@ MipsAsmParser::OperandMatchResultTy MipsAsmParser::parseMemOperand(
   if (IdVal == 0)
     IdVal = MCConstantExpr::Create(0, getContext());
 
-  // now replace register operand with the mem operand
+  // Now replace register operand with the mem operand
   MipsOperand* op = static_cast<MipsOperand*>(Operands.back());
   int RegNo = op->getReg();
-  // remove register from operands
+  // Remove register from operands
   Operands.pop_back();
-  // and add memory operand
+  // And add memory operand
+  if (const MCBinaryExpr *BE = dyn_cast<MCBinaryExpr>(IdVal)) {
+    int64_t Imm;
+    if (IdVal->EvaluateAsAbsolute(Imm))
+      IdVal = MCConstantExpr::Create(Imm, getContext());
+    else if (BE->getLHS()->getKind() != MCExpr::SymbolRef)
+      IdVal = MCBinaryExpr::Create(BE->getOpcode(), BE->getRHS(), BE->getLHS(),
+                                   getContext());
+  }
+
   Operands.push_back(MipsOperand::CreateMem(RegNo, IdVal, S, E));
   delete op;
   return MatchOperand_Success;
@@ -1160,13 +1253,13 @@ MipsAsmParser::parseCPU64Regs(SmallVectorImpl<MCParsedAsmOperand*> &Operands) {
       return MatchOperand_Success;
     return MatchOperand_NoMatch;
   }
-  // if the first token is not '$' we have an error
+  // If the first token is not '$' we have an error
   if (Parser.getTok().isNot(AsmToken::Dollar))
     return MatchOperand_NoMatch;
 
   Parser.Lex(); // Eat $
   if(!tryParseRegisterOperand(Operands, true)) {
-    // set the proper register kind
+    // Set the proper register kind
     MipsOperand* op = static_cast<MipsOperand*>(Operands.back());
     op->setRegKind(MipsOperand::Kind_CPU64Regs);
     return MatchOperand_Success;
@@ -1220,13 +1313,13 @@ MipsAsmParser::parseCPURegs(SmallVectorImpl<MCParsedAsmOperand*> &Operands) {
       return MatchOperand_Success;
     return MatchOperand_NoMatch;
   }
-  // if the first token is not '$' we have an error
+  // If the first token is not '$' we have an error
   if (Parser.getTok().isNot(AsmToken::Dollar))
     return MatchOperand_NoMatch;
 
   Parser.Lex(); // Eat $
   if(!tryParseRegisterOperand(Operands, false)) {
-    // set the propper register kind
+    // Set the propper register kind
     MipsOperand* op = static_cast<MipsOperand*>(Operands.back());
     op->setRegKind(MipsOperand::Kind_CPURegs);
     return MatchOperand_Success;
@@ -1240,18 +1333,18 @@ MipsAsmParser::parseHWRegs(SmallVectorImpl<MCParsedAsmOperand*> &Operands) {
   if (isMips64())
     return MatchOperand_NoMatch;
 
-  // if the first token is not '$' we have error
+  // If the first token is not '$' we have error
   if (Parser.getTok().isNot(AsmToken::Dollar))
     return MatchOperand_NoMatch;
   SMLoc S = Parser.getTok().getLoc();
   Parser.Lex(); // Eat $
 
-  const AsmToken &Tok = Parser.getTok(); // get next token
+  const AsmToken &Tok = Parser.getTok(); // Get next token
   if (Tok.isNot(AsmToken::Integer))
     return MatchOperand_NoMatch;
 
   unsigned RegNum = Tok.getIntVal();
-  // at the moment only hwreg29 is supported
+  // At the moment only hwreg29 is supported
   if (RegNum != 29)
     return MatchOperand_ParseFail;
 
@@ -1269,18 +1362,18 @@ MipsAsmParser::parseHW64Regs(SmallVectorImpl<MCParsedAsmOperand*> &Operands) {
 
   if (!isMips64())
     return MatchOperand_NoMatch;
-    //if the first token is not '$' we have error
+    // If the first token is not '$' we have error
   if (Parser.getTok().isNot(AsmToken::Dollar))
     return MatchOperand_NoMatch;
   SMLoc S = Parser.getTok().getLoc();
   Parser.Lex(); // Eat $
 
-  const AsmToken &Tok = Parser.getTok(); // get next token
+  const AsmToken &Tok = Parser.getTok(); // Get next token
   if (Tok.isNot(AsmToken::Integer))
     return MatchOperand_NoMatch;
 
   unsigned RegNum = Tok.getIntVal();
-  // at the moment only hwreg29 is supported
+  // At the moment only hwreg29 is supported
   if (RegNum != 29)
     return MatchOperand_ParseFail;
 
@@ -1296,20 +1389,20 @@ MipsAsmParser::parseHW64Regs(SmallVectorImpl<MCParsedAsmOperand*> &Operands) {
 MipsAsmParser::OperandMatchResultTy
 MipsAsmParser::parseCCRRegs(SmallVectorImpl<MCParsedAsmOperand*> &Operands) {
   unsigned RegNum;
-  //if the first token is not '$' we have error
+  // If the first token is not '$' we have error
   if (Parser.getTok().isNot(AsmToken::Dollar))
     return MatchOperand_NoMatch;
   SMLoc S = Parser.getTok().getLoc();
   Parser.Lex(); // Eat $
 
-  const AsmToken &Tok = Parser.getTok(); // get next token
+  const AsmToken &Tok = Parser.getTok(); // Get next token
   if (Tok.is(AsmToken::Integer)) {
     RegNum = Tok.getIntVal();
-    // at the moment only fcc0 is supported
+    // At the moment only fcc0 is supported
     if (RegNum != 0)
       return MatchOperand_ParseFail;
   } else if (Tok.is(AsmToken::Identifier)) {
-    // at the moment only fcc0 is supported
+    // At the moment only fcc0 is supported
     if (Tok.getIdentifier() != "fcc0")
       return MatchOperand_ParseFail;
   } else
@@ -1376,16 +1469,16 @@ static int ConvertCcString(StringRef CondString) {
 bool MipsAsmParser::
 parseMathOperation(StringRef Name, SMLoc NameLoc,
                    SmallVectorImpl<MCParsedAsmOperand*> &Operands) {
-  // split the format
+  // Split the format
   size_t Start = Name.find('.'), Next = Name.rfind('.');
   StringRef Format1 = Name.slice(Start, Next);
-  // and add the first format to the operands
+  // And add the first format to the operands
   Operands.push_back(MipsOperand::CreateToken(Format1, NameLoc));
-  // now for the second format
+  // Now for the second format
   StringRef Format2 = Name.slice(Next, StringRef::npos);
   Operands.push_back(MipsOperand::CreateToken(Format2, NameLoc));
 
-  // set the format for the first register
+  // Set the format for the first register
   setFpFormat(Format1);
 
   // Read the remaining operands.
@@ -1405,7 +1498,7 @@ parseMathOperation(StringRef Name, SMLoc NameLoc,
     }
     Parser.Lex();  // Eat the comma.
 
-    //set the format for the first register
+    // Set the format for the first register
     setFpFormat(Format2);
 
     // Parse and remember the operand.
@@ -1430,7 +1523,7 @@ bool MipsAsmParser::
 ParseInstruction(ParseInstructionInfo &Info, StringRef Name, SMLoc NameLoc,
                  SmallVectorImpl<MCParsedAsmOperand*> &Operands) {
   StringRef Mnemonic;
-  // floating point instructions: should register be treated as double?
+  // Floating point instructions: should register be treated as double?
   if (requestsDoubleOperand(Name)) {
     setFpFormat(FP_FORMAT_D);
   Operands.push_back(MipsOperand::CreateToken(Name, NameLoc));
@@ -1445,15 +1538,14 @@ ParseInstruction(ParseInstructionInfo &Info, StringRef Name, SMLoc NameLoc,
     Operands.push_back(MipsOperand::CreateToken(Mnemonic, NameLoc));
 
     if (Next != StringRef::npos) {
-      // there is a format token in mnemonic
-      // StringRef Rest = Name.slice(Next, StringRef::npos);
+      // There is a format token in mnemonic
       size_t Dot = Name.find('.', Next+1);
       StringRef Format = Name.slice(Next, Dot);
-      if (Dot == StringRef::npos) //only one '.' in a string, it's a format
+      if (Dot == StringRef::npos) // Only one '.' in a string, it's a format
         Operands.push_back(MipsOperand::CreateToken(Format, NameLoc));
       else {
         if (Name.startswith("c.")){
-          // floating point compare, add '.' and immediate represent for cc
+          // Floating point compare, add '.' and immediate represent for cc
           Operands.push_back(MipsOperand::CreateToken(".", NameLoc));
           int Cc = ConvertCcString(Format);
           if (Cc == -1) {
@@ -1640,12 +1732,12 @@ bool MipsAsmParser::parseSetAssignment() {
 
   if (getLexer().isNot(AsmToken::Comma))
     return reportParseError("unexpected token in .set directive");
-  Lex(); //eat comma
+  Lex(); // Eat comma
 
   if (Parser.parseExpression(Value))
     reportParseError("expected valid expression after comma");
 
-  // check if the Name already exists as a symbol
+  // Check if the Name already exists as a symbol
   MCSymbol *Sym = getContext().LookupSymbol(Name);
   if (Sym) {
     return reportParseError("symbol already defined");
@@ -1657,7 +1749,7 @@ bool MipsAsmParser::parseSetAssignment() {
 }
 bool MipsAsmParser::parseDirectiveSet() {
 
-  // get next token
+  // Get next token
   const AsmToken &Tok = Parser.getTok();
 
   if (Tok.getString() == "noat") {
@@ -1673,11 +1765,11 @@ bool MipsAsmParser::parseDirectiveSet() {
   } else if (Tok.getString() == "nomacro") {
     return parseSetNoMacroDirective();
   } else if (Tok.getString() == "nomips16") {
-    // ignore this directive for now
+    // Ignore this directive for now
     Parser.eatToEndOfStatement();
     return false;
   } else if (Tok.getString() == "nomicromips") {
-    // ignore this directive for now
+    // Ignore this directive for now
     Parser.eatToEndOfStatement();
     return false;
   } else {
@@ -1719,19 +1811,19 @@ bool MipsAsmParser::ParseDirective(AsmToken DirectiveID) {
   StringRef IDVal = DirectiveID.getString();
 
   if ( IDVal == ".ent") {
-    // ignore this directive for now
+    // Ignore this directive for now
     Parser.Lex();
     return false;
   }
 
   if (IDVal == ".end") {
-    // ignore this directive for now
+    // Ignore this directive for now
     Parser.Lex();
     return false;
   }
 
   if (IDVal == ".frame") {
-    // ignore this directive for now
+    // Ignore this directive for now
     Parser.eatToEndOfStatement();
     return false;
   }
@@ -1741,19 +1833,19 @@ bool MipsAsmParser::ParseDirective(AsmToken DirectiveID) {
   }
 
   if (IDVal == ".fmask") {
-    // ignore this directive for now
+    // Ignore this directive for now
     Parser.eatToEndOfStatement();
     return false;
   }
 
   if (IDVal == ".mask") {
-    // ignore this directive for now
+    // Ignore this directive for now
     Parser.eatToEndOfStatement();
     return false;
   }
 
   if (IDVal == ".gpword") {
-    // ignore this directive for now
+    // Ignore this directive for now
     Parser.eatToEndOfStatement();
     return false;
   }
diff --git a/lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.cpp b/lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.cpp
index e198a7c983f..5cdbcf4fe21 100644
--- a/lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.cpp
+++ b/lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.cpp
@@ -88,6 +88,9 @@ public:
   unsigned getSizeInsEncoding(const MCInst &MI, unsigned OpNo,
                               SmallVectorImpl<MCFixup> &Fixups) const;
 
+  unsigned
+  getExprOpValue(const MCExpr *Expr,SmallVectorImpl<MCFixup> &Fixups) const;
+
 }; // class MipsMCCodeEmitter
 }  // namespace
 
@@ -192,35 +195,24 @@ getJumpTargetOpValue(const MCInst &MI, unsigned OpNo,
   return 0;
 }
 
-/// getMachineOpValue - Return binary encoding of operand. If the machine
-/// operand requires relocation, record the relocation and return zero.
 unsigned MipsMCCodeEmitter::
-getMachineOpValue(const MCInst &MI, const MCOperand &MO,
-                  SmallVectorImpl<MCFixup> &Fixups) const {
-  if (MO.isReg()) {
-    unsigned Reg = MO.getReg();
-    unsigned RegNo = Ctx.getRegisterInfo().getEncodingValue(Reg);
-    return RegNo;
-  } else if (MO.isImm()) {
-    return static_cast<unsigned>(MO.getImm());
-  } else if (MO.isFPImm()) {
-    return static_cast<unsigned>(APFloat(MO.getFPImm())
-        .bitcastToAPInt().getHiBits(32).getLimitedValue());
-  }
+getExprOpValue(const MCExpr *Expr,SmallVectorImpl<MCFixup> &Fixups) const {
+  int64_t Res;
 
-  // MO must be an Expr.
-  assert(MO.isExpr());
+  if (Expr->EvaluateAsAbsolute(Res))
+    return Res;
 
-  const MCExpr *Expr = MO.getExpr();
   MCExpr::ExprKind Kind = Expr->getKind();
+  if (Kind == MCExpr::Constant) {
+    return cast<MCConstantExpr>(Expr)->getValue();
+  }
 
   if (Kind == MCExpr::Binary) {
-    Expr = static_cast<const MCBinaryExpr*>(Expr)->getLHS();
-    Kind = Expr->getKind();
+    unsigned Res = getExprOpValue(cast<MCBinaryExpr>(Expr)->getLHS(), Fixups);
+    Res += getExprOpValue(cast<MCBinaryExpr>(Expr)->getRHS(), Fixups);
+    return Res;
   }
-
-  assert (Kind == MCExpr::SymbolRef);
-
+  if (Kind == MCExpr::SymbolRef) {
   Mips::Fixups FixupKind = Mips::Fixups(0);
 
   switch(cast<MCSymbolRefExpr>(Expr)->getKind()) {
@@ -300,12 +292,32 @@ getMachineOpValue(const MCInst &MI, const MCOperand &MO,
     break;
   } // switch
 
-  Fixups.push_back(MCFixup::Create(0, MO.getExpr(), MCFixupKind(FixupKind)));
-
-  // All of the information is in the fixup.
+    Fixups.push_back(MCFixup::Create(0, Expr, MCFixupKind(FixupKind)));
+    return 0;
+  }
   return 0;
 }
 
+/// getMachineOpValue - Return binary encoding of operand. If the machine
+/// operand requires relocation, record the relocation and return zero.
+unsigned MipsMCCodeEmitter::
+getMachineOpValue(const MCInst &MI, const MCOperand &MO,
+                  SmallVectorImpl<MCFixup> &Fixups) const {
+  if (MO.isReg()) {
+    unsigned Reg = MO.getReg();
+    unsigned RegNo = Ctx.getRegisterInfo().getEncodingValue(Reg);
+    return RegNo;
+  } else if (MO.isImm()) {
+    return static_cast<unsigned>(MO.getImm());
+  } else if (MO.isFPImm()) {
+    return static_cast<unsigned>(APFloat(MO.getFPImm())
+        .bitcastToAPInt().getHiBits(32).getLimitedValue());
+  }
+  // MO must be an Expr.
+  assert(MO.isExpr());
+  return getExprOpValue(MO.getExpr(),Fixups);
+}
+
 /// getMemEncoding - Return binary encoding of memory related operand.
 /// If the offset operand requires relocation, record the relocation.
 unsigned
diff --git a/test/MC/Mips/expr1.s b/test/MC/Mips/expr1.s
new file mode 100644
index 00000000000..67664c1a2ae
--- /dev/null
+++ b/test/MC/Mips/expr1.s
@@ -0,0 +1,26 @@
+# RUN: llvm-mc  %s -triple=mipsel-unknown-linux -show-encoding -mcpu=mips32r2 | FileCheck %s
+# Check that the assembler can handle the expressions as operands.
+# CHECK:  .text
+# CHECK:  .globl  foo
+# CHECK:  foo:
+# CHECK:  lw   $4, %lo(foo)($4)    # encoding: [A,A,0x84,0x8c]
+# CHECK:                           #   fixup A - offset: 0, value: foo@ABS_LO, kind: fixup_Mips_LO16
+# CHECK:  lw   $4, 56($4)          # encoding: [0x38,0x00,0x84,0x8c]
+# CHECK:  lw   $4, %lo(foo+8)($4)  # encoding: [0x08'A',A,0x84,0x8c]
+# CHECK:                           #   fixup A - offset: 0, value: foo@ABS_LO, kind: fixup_Mips_LO16
+# CHECK:  lw   $4, %lo(foo+8)($4)  # encoding: [0x08'A',A,0x84,0x8c]
+# CHECK:                           #   fixup A - offset: 0, value: foo@ABS_LO, kind: fixup_Mips_LO16
+# CHECK:  lw   $4, %lo(foo+8)($4)  # encoding: [0x08'A',A,0x84,0x8c]
+# CHECK:                           #   fixup A - offset: 0, value: foo@ABS_LO, kind: fixup_Mips_LO16
+# CHECK:  .space  64
+
+  .globl  foo
+  .ent  foo
+foo:
+  lw  $4,%lo(foo)($4)
+  lw  $4,((10 + 4) * 4)($4)
+  lw  $4,%lo (2 * 4) + foo($4)
+  lw  $4,%lo((2 * 4) + foo)($4)
+  lw  $4,(((%lo ((2 * 4) + foo))))($4)
+  .space  64
+  .end  foo