[LCG] Hoist the main DFS loop out of the edge removal function. This
makes working through the worklist much cleaner, and makes it possible
to avoid the 'bool-to-continue-the-outer-loop' hack. Not a huge
difference, but I think this is approaching as polished as I can make
it.
llvm-svn: 207310
diff --git a/llvm/lib/Analysis/LazyCallGraph.cpp b/llvm/lib/Analysis/LazyCallGraph.cpp
index 45d289b..1e7f796 100644
--- a/llvm/lib/Analysis/LazyCallGraph.cpp
+++ b/llvm/lib/Analysis/LazyCallGraph.cpp
@@ -180,6 +180,86 @@
G.LeafSCCs.push_back(this);
}
+void LazyCallGraph::SCC::internalDFS(
+ LazyCallGraph &G,
+ SmallVectorImpl<std::pair<Node *, Node::iterator>> &DFSStack,
+ SmallVectorImpl<Node *> &PendingSCCStack, Node *N,
+ SmallVectorImpl<SCC *> &ResultSCCs) {
+ Node::iterator I = N->begin();
+ N->LowLink = N->DFSNumber = 1;
+ int NextDFSNumber = 2;
+ for (;;) {
+ assert(N->DFSNumber != 0 && "We should always assign a DFS number "
+ "before processing a node.");
+
+ // We simulate recursion by popping out of the nested loop and continuing.
+ Node::iterator E = N->end();
+ while (I != E) {
+ Node &ChildN = *I;
+ if (SCC *ChildSCC = G.SCCMap.lookup(&ChildN)) {
+ // Check if we have reached a node in the new (known connected) set of
+ // this SCC. If so, the entire stack is necessarily in that set and we
+ // can re-start.
+ if (ChildSCC == this) {
+ insert(G, *N);
+ while (!PendingSCCStack.empty())
+ insert(G, *PendingSCCStack.pop_back_val());
+ while (!DFSStack.empty())
+ insert(G, *DFSStack.pop_back_val().first);
+ return;
+ }
+
+ // 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.
+ ChildSCC->ParentSCCs.erase(this);
+ ++I;
+ continue;
+ }
+
+ 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.
+ DFSStack.push_back(std::make_pair(N, I));
+
+ // Continue, resetting to the child node.
+ ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
+ N = &ChildN;
+ I = ChildN.begin();
+ E = ChildN.end();
+ continue;
+ }
+
+ // Track the lowest link of the childen, if any are still in the stack.
+ // Any child not on the stack will have a LowLink of -1.
+ assert(ChildN.LowLink != 0 &&
+ "Low-link must not be zero with a non-zero DFS number.");
+ if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
+ N->LowLink = ChildN.LowLink;
+ ++I;
+ }
+
+ if (N->LowLink == N->DFSNumber) {
+ ResultSCCs.push_back(G.formSCC(N, PendingSCCStack));
+ if (DFSStack.empty())
+ return;
+ } else {
+ // 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);
+
+ assert(!DFSStack.empty() && "We shouldn't have an empty stack!");
+ }
+
+ N = DFSStack.back().first;
+ I = DFSStack.back().second;
+ DFSStack.pop_back();
+ }
+}
+
SmallVector<LazyCallGraph::SCC *, 1>
LazyCallGraph::SCC::removeInternalEdge(LazyCallGraph &G, Node &Caller,
Node &Callee) {
@@ -192,11 +272,6 @@
if (&Caller == &Callee)
return ResultSCCs;
- // 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.
SmallVector<Node *, 1> Worklist;
Worklist.swap(Nodes);
@@ -217,96 +292,17 @@
// walk.
insert(G, Callee);
- Node *N = nullptr;
- Node::iterator ChildI;
- for (;;) {
- if (!N) {
- if (!DFSStack.empty()) {
- N = DFSStack.back().first;
- ChildI = DFSStack.back().second;
- DFSStack.pop_back();
- } else {
- // 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;
- N = Worklist.pop_back_val();
- N->LowLink = N->DFSNumber = 1;
- NextDFSNumber = 2;
- ChildI = N->begin();
- assert(PendingSCCStack.empty() && "Cannot start a fresh DFS walk with "
- "pending nodes from a prior walk.");
- }
- }
- assert(N->DFSNumber != 0 && "We should always assign a DFS number "
- "before processing a node.");
+ // We're going to do a full mini-Tarjan's walk using a local stack here.
+ SmallVector<std::pair<Node *, Node::iterator>, 4> DFSStack;
+ SmallVector<Node *, 4> PendingSCCStack;
+ do {
+ Node *N = Worklist.pop_back_val();
+ if (N->DFSNumber == 0)
+ internalDFS(G, DFSStack, PendingSCCStack, N, ResultSCCs);
- // We simulate recursion by popping out of the nested loop and continuing.
- bool Recurse = false;
- for (auto I = ChildI, E = N->end(); I != E; ++I) {
- Node &ChildN = *I;
- if (SCC *ChildSCC = G.SCCMap.lookup(&ChildN)) {
- // Check if we have reached a node in the new (known connected) set of
- // this SCC. If so, the entire stack is necessarily in that set and we
- // can re-start.
- if (ChildSCC == this) {
- insert(G, *N);
- while (!PendingSCCStack.empty())
- insert(G, *PendingSCCStack.pop_back_val());
- while (!DFSStack.empty())
- insert(G, *DFSStack.pop_back_val().first);
- N = nullptr;
- Recurse = true;
- break;
- }
-
- // 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.
- ChildSCC->ParentSCCs.erase(this);
- continue;
- }
-
- 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.
- DFSStack.push_back(std::make_pair(N, I));
-
- // Recurse onto this node via a tail call.
- ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
- N = &ChildN;
- ChildI = ChildN.begin();
- Recurse = true;
- break;
- }
-
- // Track the lowest link of the childen, if any are still in the stack.
- // Any child not on the stack will have a LowLink of -1.
- assert(ChildN.LowLink != 0 &&
- "Low-link must not be zero with a non-zero DFS number.");
- if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
- N->LowLink = ChildN.LowLink;
- }
- if (Recurse)
- continue;
-
- if (N->LowLink != N->DFSNumber) {
- // 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);
-
- assert(!DFSStack.empty() && "We shouldn't have an empty stack!");
- N = nullptr;
- continue;
- }
-
- ResultSCCs.push_back(G.formSCC(N, PendingSCCStack));
- N = nullptr;
- }
+ assert(DFSStack.empty() && "Didn't flush the entire DFS stack!");
+ assert(PendingSCCStack.empty() && "Didn't flush all pending SCC nodes!");
+ } while (!Worklist.empty());
// Now we need to reconnect the current SCC to the graph.
bool IsLeafSCC = true;