Subzero: Improve the use of NodeList objects.

src/IceCfg.cpp

@@ -148,7 +148,7 @@ void Cfg::reorderNodes() {
         continue;
       }
       Node->setNeedsPlacement(false);
-      if (Node != getEntryNode() && Node->getInEdges().size() == 0) {
+      if (Node != getEntryNode() && Node->getInEdges().empty()) {
         // The node has essentially been deleted since it is not a
         // successor of any other node.
         Unreachable.push_back(Node);
@@ -164,7 +164,7 @@ void Cfg::reorderNodes() {
 
       // If it's a (non-critical) edge where the successor has a single
       // in-edge, then place it before the successor.
-      CfgNode *Succ = Node->getOutEdges()[0];
+      CfgNode *Succ = Node->getOutEdges().front();
       if (Succ->getInEdges().size() == 1 &&
           PlaceIndex[Succ->getIndex()] != NoPlace) {
         Placed.insert(PlaceIndex[Succ->getIndex()], Node);
@@ -173,7 +173,7 @@ void Cfg::reorderNodes() {
       }
 
       // Otherwise, place it after the (first) predecessor.
-      CfgNode *Pred = Node->getInEdges()[0];
+      CfgNode *Pred = Node->getInEdges().front();
       auto PredPosition = PlaceIndex[Pred->getIndex()];
       // It shouldn't be the case that PredPosition==NoPlace, but if
       // that somehow turns out to be true, we just insert Node before
@@ -189,12 +189,14 @@ void Cfg::reorderNodes() {
   }
 
   // Reorder Nodes according to the built-up lists.
-  SizeT Cur = 0;
+  SizeT OldSize = Nodes.size();
+  (void)OldSize;
+  Nodes.clear();
   for (CfgNode *Node : Placed)
-    Nodes[Cur++] = Node;
+    Nodes.push_back(Node);
   for (CfgNode *Node : Unreachable)
-    Nodes[Cur++] = Node;
-  assert(Cur == Nodes.size());
+    Nodes.push_back(Node);
+  assert(Nodes.size() == OldSize);
 }
 
 void Cfg::doArgLowering() {

src/IceCfgNode.cpp

@@ -750,7 +750,7 @@ void CfgNode::livenessPostprocess(LivenessMode Mode, Liveness *Liveness) {
 // unconditional branch, contract the node by repointing all its
 // in-edges to its successor.
 void CfgNode::contractIfEmpty() {
-  if (InEdges.size() == 0)
+  if (InEdges.empty())
     return;
   Inst *Branch = NULL;
   for (Inst *I : Insts) {
@@ -763,18 +763,23 @@ void CfgNode::contractIfEmpty() {
   }
   Branch->setDeleted();
   assert(OutEdges.size() == 1);
-  // Repoint all this node's in-edges to this node's successor.
-  for (CfgNode *Pred : InEdges) {
-    for (auto I = Pred->OutEdges.begin(), E = Pred->OutEdges.end(); I != E;
-         ++I) {
-      if (*I == this) {
-        *I = OutEdges[0];
-        OutEdges[0]->InEdges.push_back(Pred);
+  // Repoint all this node's in-edges to this node's successor, unless
+  // this node's successor is actually itself (in which case the
+  // statement "OutEdges.front()->InEdges.push_back(Pred)" could
+  // invalidate the iterator over this->InEdges).
+  if (OutEdges.front() != this) {
+    for (CfgNode *Pred : InEdges) {
+      for (auto I = Pred->OutEdges.begin(), E = Pred->OutEdges.end(); I != E;
+           ++I) {
+        if (*I == this) {
+          *I = OutEdges.front();
+          OutEdges.front()->InEdges.push_back(Pred);
+        }
+      }
+      for (Inst *I : Pred->getInsts()) {
+        if (!I->isDeleted())
+          I->repointEdge(this, OutEdges.front());
       }
-    }
-    for (Inst *I : Pred->getInsts()) {
-      if (!I->isDeleted())
-        I->repointEdge(this, OutEdges[0]);
     }
   }
   InEdges.clear();

src/IceTargetLoweringX8632.cpp

@@ -4184,7 +4184,7 @@ void TargetX8632::lowerPhiAssignments(CfgNode *Node,
   assert(Node->getOutEdges().size() == 1);
   assert(Node->getInsts().empty());
   assert(Node->getPhis().empty());
-  CfgNode *Succ = Node->getOutEdges()[0];
+  CfgNode *Succ = Node->getOutEdges().front();
   getContext().init(Node);
   // Register set setup similar to regAlloc() and postLower().
   RegSetMask RegInclude = RegSet_All;

src/PNaClTranslator.cpp

@@ -1637,7 +1637,7 @@ void FunctionParser::ExitBlock() {
   // insert unreachable. This shouldn't happen, but be safe.
   unsigned Index = 0;
   for (Ice::CfgNode *Node : Func->getNodes()) {
-    if (Node->getInsts().size() == 0) {
+    if (Node->getInsts().empty()) {
       std::string Buffer;
       raw_string_ostream StrBuf(Buffer);
       StrBuf << "Basic block " << Index << " contains no instructions";
@@ -1908,7 +1908,7 @@ void FunctionParser::ProcessRecord() {
     // RET: [opval?]
     if (!isValidRecordSizeInRange(0, 1, "function block ret"))
       return;
-    if (Values.size() == 0) {
+    if (Values.empty()) {
       CurrentNode->appendInst(Ice::InstRet::create(Func));
     } else {
       CurrentNode->appendInst(