[LCG] Rather than doing a linear time SmallSetVector removal of each

child from the worklist, wait until we actually need to pop another
element off of the worklist and skip over any that were already visited
by the DFS. This also enables swapping the nodes of the SCC into the
worklist. No functionality changed.

llvm-svn: 207212

1 files changed, 7 insertions, 6 deletions

diff --git a/llvm/lib/Analysis/LazyCallGraph.cpp b/llvm/lib/Analysis/LazyCallGraph.cpp
index 871787154b4..bcefd4f24d5 100644
--- a/llvm/lib/Analysis/LazyCallGraph.cpp
+++ b/llvm/lib/Analysis/LazyCallGraph.cpp
@@ -187,14 +187,13 @@ LazyCallGraph::SCC::removeInternalEdge(LazyCallGraph &G, Node &Caller,
   SmallVector<std::pair<Node *, Node::iterator>, 4> DFSStack;
   SmallVector<Node *, 4> PendingSCCStack;
 
-  // The worklist is every node in the original SCC. FIXME: switch the SCC to
-  // use a SmallSetVector and swap here.
-  SmallSetVector<Node *, 1> Worklist;
-  for (Node *N : Nodes) {
+  // The worklist is every node in the original SCC.
+  SmallVector<Node *, 1> Worklist;
+  Worklist.swap(Nodes);
+  for (Node *N : Worklist) {
     // Clear these to 0 while we re-run Tarjan's over the SCC.
     N->DFSNumber = 0;
     N->LowLink = 0;
-    Worklist.insert(N);
   }
 
   // The callee can already reach every node in this SCC (by definition). It is
@@ -208,6 +207,9 @@ LazyCallGraph::SCC::removeInternalEdge(LazyCallGraph &G, Node &Caller,
 
   for (;;) {
     if (DFSStack.empty()) {
+      // Clear off any nodes which have already been visited in the DFS.
+      while (!Worklist.empty() && Worklist.back()->DFSNumber != 0)
+        Worklist.pop_back();
       if (Worklist.empty())
         break;
       Node *N = Worklist.pop_back_val();
@@ -253,7 +255,6 @@ LazyCallGraph::SCC::removeInternalEdge(LazyCallGraph &G, Node &Caller,
 
         // Recurse onto this node via a tail call.
         ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
-        Worklist.remove(&ChildN);
         DFSStack.push_back(std::make_pair(&ChildN, ChildN.begin()));
         Recurse = true;
         break;