Subzero: Slight improvement to phi lowering.

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.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 255 matching lines @@
     // The following code does an in-place update of liveness and live ranges as
     // a result of adding the new phi edge split nodes.
     getLiveness()->initPhiEdgeSplits(Nodes.begin() + NumNodes,
                                      Variables.begin() + NumVars);
     TimerMarker TTT(TimerStack::TT_liveness, this);
     // Iterate over the newly added nodes to add their liveness info.
     for (auto I = Nodes.begin() + NumNodes, E = Nodes.end(); I != E; ++I) {
       InstNumberT FirstInstNum = getNextInstNumber();
       (*I)->renumberInstructions();
       InstNumberT LastInstNum = getNextInstNumber() - 1;
-      // TODO(stichnot): May be able to speed up liveness and live range
-      // calculation by having it consider only pre-colored or infinite-weight
-      // variables.  Could also simplify LinearScan::initForInfOnly() that way.
       (*I)->liveness(getLiveness());
       (*I)->livenessAddIntervals(getLiveness(), FirstInstNum, LastInstNum);
     }
   } else {
     // The following code does a brute-force recalculation of live ranges as a
     // result of adding the new phi edge split nodes.  The liveness calculation
     // is particularly expensive because the new nodes are not yet in a proper
     // topological order and so convergence is slower.
     //
     // This code is kept here for reference and can be temporarily enabled in
@@ skipping 471 matching lines @@
     }
   }
   // Print each basic block
   for (CfgNode *Node : Nodes)
     Node->dump(this);
   if (isVerbose(IceV_Instructions))
     Str << "}\n";
 }
 
 } // end of namespace Ice