From 9a1fab37c72e134bfca980bd69a58a593a7bc148 Mon Sep 17 00:00:00 2001
From: Chandler Carruth <chandlerc@gmail.com>
Date: Sat, 26 Apr 2014 09:45:55 +0000
Subject: [PATCH] [LCG] Rather than removing nodes from the SCC entry set when
 we process them, just skip over any DFS-numbered nodes when finding the next
 root of a DFS. This allows the entry set to just be a vector as we populate
 it from a uniqued source. It also removes the possibility for a linear scan
 of the entry set to actually do the removal which can make things go
 quadratic if we get unlucky.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207312 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Analysis/LazyCallGraph.h |  2 +-
 lib/Analysis/LazyCallGraph.cpp        | 13 +++++++------
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/include/llvm/Analysis/LazyCallGraph.h b/include/llvm/Analysis/LazyCallGraph.h
index d4b2d354f18..07ba0004bd8 100644
--- a/include/llvm/Analysis/LazyCallGraph.h
+++ b/include/llvm/Analysis/LazyCallGraph.h
@@ -384,7 +384,7 @@ private:
   SmallVector<std::pair<Node *, iterator>, 4> DFSStack;
 
   /// \brief Set of entry nodes not-yet-processed into SCCs.
-  SmallSetVector<Function *, 4> SCCEntryNodes;
+  SmallVector<Function *, 4> SCCEntryNodes;
 
   /// \brief Stack of nodes the DFS has walked but not yet put into a SCC.
   SmallVector<Node *, 4> PendingSCCStack;
diff --git a/lib/Analysis/LazyCallGraph.cpp b/lib/Analysis/LazyCallGraph.cpp
index 50accb3a753..196003430a4 100644
--- a/lib/Analysis/LazyCallGraph.cpp
+++ b/lib/Analysis/LazyCallGraph.cpp
@@ -100,9 +100,9 @@ LazyCallGraph::LazyCallGraph(Module &M) : NextDFSNumber(0) {
 
   for (auto &Entry : EntryNodes)
     if (Function *F = Entry.dyn_cast<Function *>())
-      SCCEntryNodes.insert(F);
+      SCCEntryNodes.push_back(F);
     else
-      SCCEntryNodes.insert(&Entry.get<Node *>()->getFunction());
+      SCCEntryNodes.push_back(&Entry.get<Node *>()->getFunction());
 }
 
 LazyCallGraph::LazyCallGraph(LazyCallGraph &&G)
@@ -437,10 +437,12 @@ LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
     DFSStack.pop_back();
   } else {
     // If we've handled all candidate entry nodes to the SCC forest, we're done.
-    if (SCCEntryNodes.empty())
-      return nullptr;
+    do {
+      if (SCCEntryNodes.empty())
+        return nullptr;
 
-    N = &get(*SCCEntryNodes.pop_back_val());
+      N = &get(*SCCEntryNodes.pop_back_val());
+    } while (N->DFSNumber != 0);
     I = N->begin();
     N->LowLink = N->DFSNumber = 1;
     NextDFSNumber = 2;
@@ -463,7 +465,6 @@ LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
         assert(!SCCMap.count(&ChildN) &&
                "Found a node with 0 DFS number but already in an SCC!");
         ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
-        SCCEntryNodes.remove(&ChildN.getFunction());
         N = &ChildN;
         I = ChildN.begin();
         E = ChildN.end();