Add support for passing and returning vectors in accordance with the x86 calling convention.

src/IceOperand.h

 //===- subzero/src/IceOperand.h - High-level operands -----------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file declares the Operand class and its target-independent
@@ skipping 321 matching lines @@
 
   Inst *getDefinition() const { return DefInst; }
   void setDefinition(Inst *Inst, const CfgNode *Node);
   void replaceDefinition(Inst *Inst, const CfgNode *Node);
 
   const CfgNode *getLocalUseNode() const { return DefNode; }
   bool isMultiblockLife() const { return (DefNode == NULL); }
   void setUse(const Inst *Inst, const CfgNode *Node);
 
   bool getIsArg() const { return IsArgument; }
-  void setIsArg(Cfg *Func);
+  void setIsArg(Cfg *Func, bool IsArg = true);
 
   int32_t getStackOffset() const { return StackOffset; }
   void setStackOffset(int32_t Offset) { StackOffset = Offset; }
 
   static const int32_t NoRegister = -1;
   bool hasReg() const { return getRegNum() != NoRegister; }
   int32_t getRegNum() const { return RegNum; }
   void setRegNum(int32_t NewRegNum) {
     // Regnum shouldn't be set more than once.
     assert(!hasReg() || RegNum == NewRegNum);
@@ skipping 110 matching lines @@
   Variable *LoVar;
   Variable *HiVar;
   // VarsReal (and Operand::Vars) are set up such that Vars[0] ==
   // this.
   Variable *VarsReal[1];
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEOPERAND_H