Subzero: Improve performance of liveness analysis and live range construction.

src/IceOperand.cpp

Index: src/IceOperand.cpp
diff --git a/src/IceOperand.cpp b/src/IceOperand.cpp
index 9ecfd317d3872d5bf1d1223f5c35bdea535d9492..f75f1171da4408bc3a591f3bea2c971b83804fbc 100644
--- a/src/IceOperand.cpp
+++ b/src/IceOperand.cpp
@@ -184,6 +184,8 @@ Variable Variable::asType(Type Ty) {
 
 void VariableTracking::markUse(const Inst *Instr, const CfgNode *Node,
                                bool IsFromDef, bool IsImplicit) {
+  if (MultiBlock == MBS_MultiBlock)
+    return;
   // TODO(stichnot): If the use occurs as a source operand in the
   // first instruction of the block, and its definition is in this
   // block's only predecessor, we might consider not marking this as a
@@ -301,9 +303,7 @@ void VariablesMetadata::init() {
     Metadata[Var->getIndex()].markUse(NoInst, EntryNode, IsFromDef, IsImplicit);
   }
 
-  SizeT NumNodes = Func->getNumNodes();
-  for (SizeT N = 0; N < NumNodes; ++N) {
-    CfgNode *Node = Func->getNodes()[N];
+  for (CfgNode *Node : Func->getNodes()) {
     for (Inst *I : Node->getInsts()) {
       if (I->isDeleted())
         continue;