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[LCG] Hoist the logic for forming a new SCC from the top of the DFSStack

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into a helper function. I plan to re-use it for doing incremental
DFS-based updates to the SCCs when we mutate the call graph.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206948 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2014-04-23 06:09:03 +00:00
parent b3112f6acc
commit b001573515
2 changed files with 52 additions and 41 deletions
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5
include/llvm/Analysis/LazyCallGraph.h
View File

@ -364,6 +364,11 @@ private:
/// \brief Helper to update pointers back to the graph object during moves.
void updateGraphPtrs();
/// \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);
/// \brief Retrieve the next node in the post-order SCC walk of the call graph.
SCC *getNextSCCInPostOrder();
};

88
lib/Analysis/LazyCallGraph.cpp
View File

@ -151,6 +151,51 @@ void LazyCallGraph::updateGraphPtrs() {
}
}
LazyCallGraph::SCC *LazyCallGraph::formSCCFromDFSStack(
SmallVectorImpl<std::pair<Node *, Node::iterator>> &DFSStack) {
// The tail of the stack is the new SCC. Allocate the SCC and pop the stack
// into it.
SCC *NewSCC = new (SCCBPA.Allocate()) SCC();
// Because we don't follow the strict Tarjan recursive formulation, walk
// from the top of the stack down, propagating the lowest link and stopping
// when the DFS number is the lowest link.
int LowestLink = DFSStack.back().first->LowLink;
do {
Node *SCCN = DFSStack.pop_back_val().first;
SCCMap[&SCCN->getFunction()] = NewSCC;
NewSCC->Nodes.push_back(SCCN);
LowestLink = std::min(LowestLink, SCCN->LowLink);
bool Inserted =
NewSCC->NodeSet.insert(&SCCN->getFunction());
(void)Inserted;
assert(Inserted && "Cannot have duplicates in the DFSStack!");
} while (!DFSStack.empty() && LowestLink <= DFSStack.back().first->DFSNumber);
assert(LowestLink == NewSCC->Nodes.back()->DFSNumber &&
"Cannot stop with a DFS number greater than the lowest link!");
// 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
// its children.
bool IsLeafSCC = true;
for (Node *SCCN : NewSCC->Nodes)
for (Node *SCCChildN : *SCCN) {
if (NewSCC->NodeSet.count(&SCCChildN->getFunction()))
continue;
SCC *ChildSCC = SCCMap.lookup(&SCCChildN->getFunction());
assert(ChildSCC &&
"Must have all child SCCs processed when building a new SCC!");
ChildSCC->ParentSCCs.insert(NewSCC);
IsLeafSCC = false;
}
// For the SCCs where we fine no child SCCs, add them to the leaf list.
if (IsLeafSCC)
LeafSCCs.push_back(NewSCC);
return NewSCC;
}
LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
// When the stack is empty, there are no more SCCs to walk in this graph.
if (DFSStack.empty()) {
@ -190,47 +235,8 @@ LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
N->LowLink = ChildN->LowLink;
}
// The tail of the stack is the new SCC. Allocate the SCC and pop the stack
// into it.
SCC *NewSCC = new (SCCBPA.Allocate()) SCC();
// Because we don't follow the strict Tarjan recursive formulation, walk
// from the top of the stack down, propagating the lowest link and stopping
// when the DFS number is the lowest link.
int LowestLink = N->LowLink;
do {
Node *SCCN = DFSStack.pop_back_val().first;
SCCMap.insert(std::make_pair(&SCCN->getFunction(), NewSCC));
NewSCC->Nodes.push_back(SCCN);
LowestLink = std::min(LowestLink, SCCN->LowLink);
bool Inserted =
NewSCC->NodeSet.insert(&SCCN->getFunction());
(void)Inserted;
assert(Inserted && "Cannot have duplicates in the DFSStack!");
} while (!DFSStack.empty() && LowestLink <= DFSStack.back().first->DFSNumber);
assert(LowestLink == NewSCC->Nodes.back()->DFSNumber &&
"Cannot stop with a DFS number greater than the lowest link!");
// 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
// its children.
bool IsLeafSCC = true;
for (Node *SCCN : NewSCC->Nodes)
for (Node *SCCChildN : *SCCN) {
if (NewSCC->NodeSet.count(&SCCChildN->getFunction()))
continue;
SCC *ChildSCC = SCCMap.lookup(&SCCChildN->getFunction());
assert(ChildSCC &&
"Must have all child SCCs processed when building a new SCC!");
ChildSCC->ParentSCCs.insert(NewSCC);
IsLeafSCC = false;
}
// For the SCCs where we fine no child SCCs, add them to the leaf list.
if (IsLeafSCC)
LeafSCCs.push_back(NewSCC);
return NewSCC;
// Form the new SCC out of the top of the DFS stack.
return formSCCFromDFSStack(DFSStack);
}
char LazyCallGraphAnalysis::PassID;