[llvm] r207310 - [LCG] Hoist the main DFS loop out of the edge removal function. This
Chandler Carruth
chandlerc at gmail.com
Sat Apr 26 02:06:56 PDT 2014
Author: chandlerc
Date: Sat Apr 26 04:06:53 2014
New Revision: 207310
URL: http://llvm.org/viewvc/llvm-project?rev=207310&view=rev
Log:
[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.
Modified:
llvm/trunk/include/llvm/Analysis/LazyCallGraph.h
llvm/trunk/lib/Analysis/LazyCallGraph.cpp
Modified: llvm/trunk/include/llvm/Analysis/LazyCallGraph.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/LazyCallGraph.h?rev=207310&r1=207309&r2=207310&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/LazyCallGraph.h (original)
+++ llvm/trunk/include/llvm/Analysis/LazyCallGraph.h Sat Apr 26 04:06:53 2014
@@ -227,6 +227,12 @@ public:
void removeEdge(LazyCallGraph &G, Function &Caller, Function &Callee,
SCC &CalleeC);
+ void
+ internalDFS(LazyCallGraph &G,
+ SmallVectorImpl<std::pair<Node *, Node::iterator>> &DFSStack,
+ SmallVectorImpl<Node *> &PendingSCCStack, Node *N,
+ SmallVectorImpl<SCC *> &ResultSCCs);
+
SmallVector<LazyCallGraph::SCC *, 1>
removeInternalEdge(LazyCallGraph &G, Node &Caller, Node &Callee);
Modified: llvm/trunk/lib/Analysis/LazyCallGraph.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/LazyCallGraph.cpp?rev=207310&r1=207309&r2=207310&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/LazyCallGraph.cpp (original)
+++ llvm/trunk/lib/Analysis/LazyCallGraph.cpp Sat Apr 26 04:06:53 2014
@@ -180,71 +180,21 @@ void LazyCallGraph::SCC::removeEdge(Lazy
G.LeafSCCs.push_back(this);
}
-SmallVector<LazyCallGraph::SCC *, 1>
-LazyCallGraph::SCC::removeInternalEdge(LazyCallGraph &G, Node &Caller,
- Node &Callee) {
- // We return a list of the resulting SCCs, where 'this' is always the first
- // element.
- SmallVector<SCC *, 1> ResultSCCs;
- ResultSCCs.push_back(this);
-
- // Direct recursion doesn't impact the SCC graph at all.
- 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);
- for (Node *N : Worklist) {
- // The nodes formerly in this SCC are no longer in any SCC.
- N->DFSNumber = 0;
- N->LowLink = 0;
- G.SCCMap.erase(N);
- }
- assert(Worklist.size() > 1 && "We have to have at least two nodes to have an "
- "edge between them that is within the SCC.");
-
- // The callee can already reach every node in this SCC (by definition). It is
- // the only node we know will stay inside this SCC. Everything which
- // transitively reaches Callee will also remain in the SCC. To model this we
- // incrementally add any chain of nodes which reaches something in the new
- // node set to the new node set. This short circuits one side of the Tarjan's
- // walk.
- insert(G, Callee);
-
- Node *N = nullptr;
- Node::iterator ChildI;
+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 (;;) {
- 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 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::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
@@ -256,14 +206,13 @@ LazyCallGraph::SCC::removeInternalEdge(L
insert(G, *PendingSCCStack.pop_back_val());
while (!DFSStack.empty())
insert(G, *DFSStack.pop_back_val().first);
- N = nullptr;
- Recurse = true;
- break;
+ 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;
}
@@ -273,12 +222,12 @@ LazyCallGraph::SCC::removeInternalEdge(L
// child's lowlink is reflected.
DFSStack.push_back(std::make_pair(N, I));
- // Recurse onto this node via a tail call.
+ // Continue, resetting to the child node.
ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
N = &ChildN;
- ChildI = ChildN.begin();
- Recurse = true;
- break;
+ I = ChildN.begin();
+ E = ChildN.end();
+ continue;
}
// Track the lowest link of the childen, if any are still in the stack.
@@ -287,11 +236,14 @@ LazyCallGraph::SCC::removeInternalEdge(L
"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 (Recurse)
- continue;
- if (N->LowLink != N->DFSNumber) {
+ 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
@@ -300,13 +252,57 @@ LazyCallGraph::SCC::removeInternalEdge(L
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;
+ N = DFSStack.back().first;
+ I = DFSStack.back().second;
+ DFSStack.pop_back();
+ }
+}
+
+SmallVector<LazyCallGraph::SCC *, 1>
+LazyCallGraph::SCC::removeInternalEdge(LazyCallGraph &G, Node &Caller,
+ Node &Callee) {
+ // We return a list of the resulting SCCs, where 'this' is always the first
+ // element.
+ SmallVector<SCC *, 1> ResultSCCs;
+ ResultSCCs.push_back(this);
+
+ // Direct recursion doesn't impact the SCC graph at all.
+ if (&Caller == &Callee)
+ return ResultSCCs;
+
+ // The worklist is every node in the original SCC.
+ SmallVector<Node *, 1> Worklist;
+ Worklist.swap(Nodes);
+ for (Node *N : Worklist) {
+ // The nodes formerly in this SCC are no longer in any SCC.
+ N->DFSNumber = 0;
+ N->LowLink = 0;
+ G.SCCMap.erase(N);
}
+ assert(Worklist.size() > 1 && "We have to have at least two nodes to have an "
+ "edge between them that is within the SCC.");
+
+ // The callee can already reach every node in this SCC (by definition). It is
+ // the only node we know will stay inside this SCC. Everything which
+ // transitively reaches Callee will also remain in the SCC. To model this we
+ // incrementally add any chain of nodes which reaches something in the new
+ // node set to the new node set. This short circuits one side of the Tarjan's
+ // walk.
+ insert(G, Callee);
+
+ // 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);
+
+ 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;
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