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[LCG] Hoist the main DFS loop out of the edge removal function. This

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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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207310 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2014-04-26 09:06:53 +00:00
parent b79f1fe084
commit 8495669112
2 changed files with 96 additions and 94 deletions
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6
include/llvm/Analysis/LazyCallGraph.h
View File

@ -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);

184
lib/Analysis/LazyCallGraph.cpp
View File

@ -180,6 +180,86 @@ void LazyCallGraph::SCC::removeEdge(LazyCallGraph &G, Function &Caller,
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 @@ LazyCallGraph::SCC::removeInternalEdge(LazyCallGraph &G, Node &Caller,
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 @@ LazyCallGraph::SCC::removeInternalEdge(LazyCallGraph &G, Node &Caller,
// 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;