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

src/IceOperand.cpp

 //===- subzero/src/IceOperand.cpp - High-level operand implementation -----===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the Operand class and its target-independent
@@ skipping 141 matching lines @@
   DefInst = Inst;
   if (Node != DefNode)
     DefNode = NULL;
 }
 
 void Variable::replaceDefinition(Inst *Inst, const CfgNode *Node) {
   DefInst = NULL;
   setDefinition(Inst, Node);
 }
 
-void Variable::setIsArg(Cfg *Func) {
-  IsArgument = true;
-  if (DefNode == NULL)
-    return;
-  CfgNode *Entry = Func->getEntryNode();
-  if (DefNode == Entry)
-    return;
-  DefNode = NULL;
+void Variable::setIsArg(Cfg *Func, bool IsArg) {
+  if (IsArg) {
+    IsArgument = true;
+    if (DefNode == NULL)
+      return;
+    CfgNode *Entry = Func->getEntryNode();
+    if (DefNode == Entry)
+      return;
+    DefNode = NULL;
+  } else {
+    IsArgument = false;
+  }
 }
 
 IceString Variable::getName() const {
   if (!Name.empty())
     return Name;
   char buf[30];
   snprintf(buf, llvm::array_lengthof(buf), "__%u", getIndex());
   return buf;
 }
 
@@ skipping 74 matching lines @@
 
 Ostream &operator<<(Ostream &Str, const RegWeight &W) {
   if (W.getWeight() == RegWeight::Inf)
     Str << "Inf";
   else
     Str << W.getWeight();
   return Str;
 }
 
 } // end of namespace Ice