diff --git a/include/llvm/Analysis/LazyCallGraph.h b/include/llvm/Analysis/LazyCallGraph.h
index b53e77b4f76..2ed3cd0d13b 100644
--- a/include/llvm/Analysis/LazyCallGraph.h
+++ b/include/llvm/Analysis/LazyCallGraph.h
@@ -370,12 +370,15 @@ private:
/// These are all of the SCCs which have no children.
SmallVector<SCC *, 4> LeafSCCs;
- /// \brief Stack of nodes not-yet-processed into SCCs.
+ /// \brief Stack of nodes in the DFS walk.
SmallVector<std::pair<Node *, iterator>, 4> DFSStack;
/// \brief Set of entry nodes not-yet-processed into SCCs.
SmallSetVector<Function *, 4> SCCEntryNodes;
+ /// \brief Stack of nodes the DFS has walked but not yet put into a SCC.
+ SmallVector<Node *, 4> PendingSCCStack;
+
/// \brief Counter for the next DFS number to assign.
int NextDFSNumber;
@@ -388,9 +391,7 @@ private:
/// \brief Helper to form a new SCC out of the top of a DFSStack-like
/// structure.
- SCC *formSCCFromDFSStack(
- SmallVectorImpl<std::pair<Node *, Node::iterator>> &DFSStack,
- SmallVectorImpl<std::pair<Node *, Node::iterator>>::iterator SCCBegin);
+ SCC *formSCC(Node *RootN, SmallVectorImpl<Node *> &NodeStack);
/// \brief Retrieve the next node in the post-order SCC walk of the call graph.
SCC *getNextSCCInPostOrder();
diff --git a/lib/Analysis/LazyCallGraph.cpp b/lib/Analysis/LazyCallGraph.cpp
index 6678aa2621b..3b727a5ee69 100644
--- a/lib/Analysis/LazyCallGraph.cpp
+++ b/lib/Analysis/LazyCallGraph.cpp
@@ -185,6 +185,7 @@ LazyCallGraph::SCC::removeInternalEdge(LazyCallGraph &G, Node &Caller,
// We're going to do a full mini-Tarjan's walk using a local stack here.
int NextDFSNumber;
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.
@@ -213,18 +214,20 @@ LazyCallGraph::SCC::removeInternalEdge(LazyCallGraph &G, Node &Caller,
N->LowLink = N->DFSNumber = 1;
NextDFSNumber = 2;
DFSStack.push_back(std::make_pair(N, N->begin()));
+ assert(PendingSCCStack.empty() && "Cannot start a fresh DFS walk with "
+ "pending nodes from a prior walk.");
}
- Node *N = DFSStack.back().first;
+ // We simulate recursion by popping out of all the nested loops and
+ // continuing.
+ bool Recurse = false;
+ do {
+ Node *N = DFSStack.back().first;
assert(N->DFSNumber != 0 && "We should always assign a DFS number "
"before placing a node onto the stack.");
- auto SI = DFSStack.rbegin();
- bool PushedChildNode = false;
- do {
- N = SI->first;
- for (auto I = SI->second, E = N->end(); I != E; ++I) {
+ for (auto I = DFSStack.back().second, E = N->end(); I != E; ++I) {
Node &ChildN = *I;
// If this child isn't currently in this SCC, no need to process it.
// However, we do need to remove this SCC from its SCC's parent set.
@@ -237,22 +240,25 @@ LazyCallGraph::SCC::removeInternalEdge(LazyCallGraph &G, Node &Caller,
// Check if we have reached a node in the new (known connected) set. If
// so, the entire stack is necessarily in that set and we can re-start.
if (NewNodes.count(&ChildN)) {
+ while (!PendingSCCStack.empty())
+ NewNodes.insert(PendingSCCStack.pop_back_val());
while (!DFSStack.empty())
NewNodes.insert(DFSStack.pop_back_val().first);
- continue;
+ Recurse = true;
+ break;
}
if (ChildN.DFSNumber == 0) {
// Mark that we should start at this child when next this node is the
// top of the stack. We don't start at the next child to ensure this
// child's lowlink is reflected.
- SI->second = I;
+ DFSStack.back().second = I;
// 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()));
- PushedChildNode = true;
+ Recurse = true;
break;
}
@@ -263,21 +269,28 @@ LazyCallGraph::SCC::removeInternalEdge(LazyCallGraph &G, Node &Caller,
if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
N->LowLink = ChildN.LowLink;
}
- if (!PushedChildNode)
- // No more children to process for this stack entry.
- SI->second = N->end();
+ if (Recurse)
+ break;
- ++SI;
- // If nothing is new on the stack and this isn't the SCC root, walk
- // upward.
- } while (!PushedChildNode && N->LowLink != N->DFSNumber &&
- SI != DFSStack.rend());
+ // No more children to process, pop it off the core DFS stack.
+ DFSStack.pop_back();
- if (DFSStack.empty() || PushedChildNode)
- continue;
+ if (N->LowLink == N->DFSNumber) {
+ ResultSCCs.push_back(G.formSCC(N, PendingSCCStack));
+ break;
+ }
- // Form the new SCC out of the top of the DFS stack.
- ResultSCCs.push_back(G.formSCCFromDFSStack(DFSStack, SI.base()));
+ assert(!DFSStack.empty() && "We shouldn't have an empty stack!");
+
+ // At this point we know that N cannot ever be an SCC root. Its low-link
+ // is not its dfs-number, and we've processed all of its children. It is
+ // just sitting here waiting until some node further down the stack gets
+ // low-link == dfs-number and pops it off as well. Move it to the pending
+ // stack which is pulled into the next SCC to be formed.
+ PendingSCCStack.push_back(N);
+ } while (!DFSStack.empty());
+
+ // We reach here when we're going to "recurse".
}
// Replace this SCC with the NewNodes we collected above.
@@ -377,23 +390,26 @@ void LazyCallGraph::updateGraphPtrs() {
}
}
-LazyCallGraph::SCC *LazyCallGraph::formSCCFromDFSStack(
- SmallVectorImpl<std::pair<Node *, Node::iterator>> &DFSStack,
- SmallVectorImpl<std::pair<Node *, Node::iterator>>::iterator SCCBegin) {
+LazyCallGraph::SCC *LazyCallGraph::formSCC(Node *RootN,
+ SmallVectorImpl<Node *> &NodeStack) {
// The tail of the stack is the new SCC. Allocate the SCC and pop the stack
// into it.
SCC *NewSCC = new (SCCBPA.Allocate()) SCC();
- for (auto I = SCCBegin, E = DFSStack.end(); I != E; ++I) {
- Node *SCCN = I->first;
- assert(SCCN->LowLink >= SCCBegin->first->LowLink &&
+ SCCMap[RootN] = NewSCC;
+ NewSCC->Nodes.push_back(RootN);
+
+ while (!NodeStack.empty() && NodeStack.back()->DFSNumber > RootN->DFSNumber) {
+ Node *SCCN = NodeStack.pop_back_val();
+ assert(SCCN->LowLink >= RootN->LowLink &&
"We cannot have a low link in an SCC lower than its root on the "
"stack!");
+ SCCN->DFSNumber = SCCN->LowLink = -1;
SCCMap[SCCN] = NewSCC;
NewSCC->Nodes.push_back(SCCN);
}
- DFSStack.erase(SCCBegin, DFSStack.end());
+ RootN->DFSNumber = RootN->LowLink = -1;
// A final pass over all edges in the SCC (this remains linear as we only
// do this once when we build the SCC) to connect it to the parent sets of
@@ -428,19 +444,18 @@ LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
DFSStack.push_back(std::make_pair(&N, N.begin()));
}
- auto SI = DFSStack.rbegin();
- assert(SI->first->DFSNumber != 0 && "We should always assign a DFS number "
- "before placing a node onto the stack.");
-
do {
- Node *N = SI->first;
- for (auto I = SI->second, E = N->end(); I != E; ++I) {
+ Node *N = DFSStack.back().first;
+ assert(N->DFSNumber != 0 && "We should always assign a DFS number "
+ "before placing a node onto the stack.");
+
+ for (auto I = DFSStack.back().second, E = N->end(); I != E; ++I) {
Node &ChildN = *I;
if (ChildN.DFSNumber == 0) {
// Mark that we should start at this child when next this node is the
// top of the stack. We don't start at the next child to ensure this
// child's lowlink is reflected.
- SI->second = I;
+ DFSStack.back().second = I;
// Recurse onto this node via a tail call.
assert(!SCCMap.count(&ChildN) &&
@@ -457,15 +472,20 @@ LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
N->LowLink = ChildN.LowLink;
}
- // No more children to process for this stack entry.
- SI->second = N->end();
+ // No more children to process here, pop the node off the stack.
+ DFSStack.pop_back();
if (N->LowLink == N->DFSNumber)
// Form the new SCC out of the top of the DFS stack.
- return formSCCFromDFSStack(DFSStack, std::prev(SI.base()));
+ return formSCC(N, PendingSCCStack);
- ++SI;
- } while (SI != DFSStack.rend());
+ // At this point we know that N cannot ever be an SCC root. Its low-link
+ // is not its dfs-number, and we've processed all of its children. It is
+ // just sitting here waiting until some node further down the stack gets
+ // low-link == dfs-number and pops it off as well. Move it to the pending
+ // stack which is pulled into the next SCC to be formed.
+ PendingSCCStack.push_back(N);
+ } while (!DFSStack.empty());
llvm_unreachable(
"We cannot reach the bottom of the stack without popping an SCC.");