Subzero: Allow delaying Phi lowering until after register allocation.

src/IceTargetLowering.cpp

 //===- subzero/src/IceTargetLowering.cpp - Basic lowering 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 skeleton of the TargetLowering class,
@@ skipping 26 matching lines @@
     "max-nops-per-instruction",
     cl::desc("Max number of nops to insert per instruction"), cl::init(1));
 
 cl::opt<int> NopProbabilityAsPercentage(
     "nop-insertion-percentage",
     cl::desc("Nop insertion probability as percentage"), cl::init(10));
 } // end of anonymous namespace
 
 void LoweringContext::init(CfgNode *N) {
   Node = N;
-  Begin = getNode()->getInsts().begin();
-  Cur = Begin;
   End = getNode()->getInsts().end();
-  skipDeleted(Cur);
-  Next = Cur;
+  rewind();
   advanceForward(Next);
 }
 
+void LoweringContext::rewind() {
+  Begin = getNode()->getInsts().begin();
+  Cur = Begin;
+  skipDeleted(Cur);
+  Next = Cur;
+}
+
 void LoweringContext::insert(Inst *Inst) {
   getNode()->getInsts().insert(Next, Inst);
   LastInserted = Inst;
 }
 
 void LoweringContext::skipDeleted(InstList::iterator &I) const {
   while (I != End && (*I)->isDeleted())
     ++I;
 }
 
@@ skipping 184 matching lines @@
   if (Target == Target_ARM64)
     return IceTargetGlobalInitARM64::create(Ctx);
 #endif
   llvm_unreachable("Unsupported target");
   return NULL;
 }
 
 TargetGlobalInitLowering::~TargetGlobalInitLowering() {}
 
 } // end of namespace Ice