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

src/IceTargetLowering.h

 //===- subzero/src/IceTargetLowering.h - Lowering interface -----*- 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 TargetLowering and LoweringContext
@@ skipping 130 matching lines @@
   };
   typedef uint32_t RegSetMask;
 
   virtual llvm::SmallBitVector getRegisterSet(RegSetMask Include,
                                               RegSetMask Exclude) const = 0;
   virtual const llvm::SmallBitVector &getRegisterSetForType(Type Ty) const = 0;
   void regAlloc();
 
   virtual void emitVariable(const Variable *Var, const Cfg *Func) const = 0;
 
+  // Performs target-specific argument lowering.
+  virtual void lowerArguments() = 0;
+
   virtual void addProlog(CfgNode *Node) = 0;
   virtual void addEpilog(CfgNode *Node) = 0;
 
   virtual void emitConstants() const = 0;
 
   virtual ~TargetLowering() {}
 
 protected:
   TargetLowering(Cfg *Func)
       : Func(Func), Ctx(Func->getContext()), HasComputedFrame(false),
@@ skipping 57 matching lines @@
 private:
   TargetGlobalInitLowering(const TargetGlobalInitLowering &)
   LLVM_DELETED_FUNCTION;
   TargetGlobalInitLowering &
   operator=(const TargetGlobalInitLowering &) LLVM_DELETED_FUNCTION;
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICETARGETLOWERING_H