From cea05a55a24ff34de7e550dd55e0149310d0db7f Mon Sep 17 00:00:00 2001
From: Chandler Carruth <chandlerc@gmail.com>
Date: Fri, 25 Apr 2014 09:08:05 +0000
Subject: [PATCH] [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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207212 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/LazyCallGraph.cpp | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/lib/Analysis/LazyCallGraph.cpp b/lib/Analysis/LazyCallGraph.cpp
index 871787154b4..bcefd4f24d5 100644
--- a/lib/Analysis/LazyCallGraph.cpp
+++ b/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;