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

src/IceCfg.cpp

 //===- subzero/src/IceCfg.cpp - Control flow graph 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 Cfg class, including constant pool
@@ skipping 99 matching lines @@
   }
 }
 
 void Cfg::doAddressOpt() {
   for (NodeList::iterator I = Nodes.begin(), E = Nodes.end(); I != E; ++I) {
     (*I)->doAddressOpt();
   }
 }
 
 void Cfg::genCode() {
+  getTarget()->lowerArguments();
   for (NodeList::iterator I = Nodes.begin(), E = Nodes.end(); I != E; ++I) {
     (*I)->genCode();
   }
 }
 
 // Compute the stack frame layout.
 void Cfg::genFrame() {
   getTarget()->addProlog(Entry);
   // TODO: Consider folding epilog generation into the final
   // emission/assembly pass to avoid an extra iteration over the node
@@ skipping 218 matching lines @@
   for (NodeList::const_iterator I = Nodes.begin(), E = Nodes.end(); I != E;
        ++I) {
     (*I)->dump(this);
   }
   if (getContext()->isVerbose(IceV_Instructions)) {
     Str << "}\n";
   }
 }
 
 } // end of namespace Ice