Subzero: Speed up VariablesMetadata initialization.

src/IceCfg.cpp

Index: src/IceCfg.cpp
diff --git a/src/IceCfg.cpp b/src/IceCfg.cpp
index c30e02a28ccdef113dc0f99122f6beeaf77584c7..72ad29b1d6de0970d84f78051ed7fee8745acbcc 100644
--- a/src/IceCfg.cpp
+++ b/src/IceCfg.cpp
@@ -168,7 +168,7 @@ void Cfg::genFrame() {
 // 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();
 }
@@ -176,7 +176,7 @@ void Cfg::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);