Subzero: Speed up VariablesMetadata initialization.

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 150 matching lines @@
     if (Node->getHasReturn())
       getTarget()->addEpilog(Node);
 }
 
 // This is a lightweight version of live-range-end calculation.  Marks
 // the last use of only those variables whose definition and uses are
 // completely with a single block.  It is a quick single pass and
 // doesn't need to iterate until convergence.
 void Cfg::livenessLightweight() {
   TimerMarker T(TimerStack::TT_livenessLightweight, this);
-  getVMetadata()->init();
+  getVMetadata()->init(VMK_Uses);
   for (CfgNode *Node : Nodes)
     Node->livenessLightweight();
 }
 
 void Cfg::liveness(LivenessMode Mode) {
   TimerMarker T(TimerStack::TT_liveness, this);
   Live.reset(new Liveness(this, Mode));
-  getVMetadata()->init();
+  getVMetadata()->init(VMK_Uses);
   Live->init();
   // Initialize with all nodes needing to be processed.
   llvm::BitVector NeedToProcess(Nodes.size(), true);
   while (NeedToProcess.any()) {
     // Iterate in reverse topological order to speed up convergence.
     // TODO(stichnot): Use llvm::make_range with LLVM 3.5.
     for (auto I = Nodes.rbegin(), E = Nodes.rend(); I != E; ++I) {
       CfgNode *Node = *I;
       if (NeedToProcess[Node->getIndex()]) {
         NeedToProcess[Node->getIndex()] = false;
@@ skipping 198 matching lines @@
     }
   }
   // Print each basic block
   for (CfgNode *Node : Nodes)
     Node->dump(this);
   if (getContext()->isVerbose(IceV_Instructions))
     Str << "}\n";
 }
 
 } // end of namespace Ice