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SCCIterator: Merge MinVisitNumStack and VisitStack

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This patch merges MinVisitNumStack with VisitStack using a StackElement
struct.

Patch by Mehdi Amini!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201353 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan P. N. Exon Smith 2014-02-13 18:26:15 +00:00
parent 62356fc694
commit efe40a5a1d
1 changed files with 38 additions and 23 deletions
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61
include/llvm/ADT/SCCIterator.h
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@ -47,6 +47,22 @@ class scc_iterator
typedef typename super::reference reference;
typedef typename super::pointer pointer;
// Element of VisitStack during DFS.
struct StackElement {
NodeType *Node; ///< The current node pointer.
ChildItTy NextChild; ///< The next child, modified inplace during DFS.
unsigned MinVisited; ///< Minimum uplink value of all children of Node.
StackElement(NodeType *Node, const ChildItTy &Child, unsigned Min)
: Node(Node), NextChild(Child), MinVisited(Min) {}
bool operator==(const StackElement &Other) const {
return Node == Other.Node &&
NextChild == Other.NextChild &&
MinVisited == Other.MinVisited;
}
};
// The visit counters used to detect when a complete SCC is on the stack.
// visitNum is the global counter.
// nodeVisitNumbers are per-node visit numbers, also used as DFS flags.
@ -59,22 +75,17 @@ class scc_iterator
// The current SCC, retrieved using operator*().
SccTy CurrentSCC;
// Used to maintain the ordering. The top is the current block, the first
// element is basic block pointer, second is the 'next child' to visit.
std::vector<std::pair<NodeType *, ChildItTy> > VisitStack;
// Stack holding the "min" values for each node in the DFS. This is used to
// track the minimum uplink values for all children of the corresponding node
// on the VisitStack.
std::vector<unsigned> MinVisitNumStack;
// DFS stack, Used to maintain the ordering. The top contains the current
// node, the next child to visit, and the minimum uplink value of all child
std::vector<StackElement> VisitStack;
// A single "visit" within the non-recursive DFS traversal.
void DFSVisitOne(NodeType *N) {
++visitNum;
nodeVisitNumbers[N] = visitNum;
SCCNodeStack.push_back(N);
MinVisitNumStack.push_back(visitNum);
VisitStack.push_back(std::make_pair(N, GT::child_begin(N)));
VisitStack.push_back(StackElement(N, GT::child_begin(N), visitNum));
#if 0 // Enable if needed when debugging.
dbgs() << "TarjanSCC: Node " << N <<
" : visitNum = " << visitNum << "\n";
@ -84,35 +95,39 @@ class scc_iterator
// The stack-based DFS traversal; defined below.
void DFSVisitChildren() {
assert(!VisitStack.empty());
while (VisitStack.back().second != GT::child_end(VisitStack.back().first)) {
while (VisitStack.back().NextChild !=
GT::child_end(VisitStack.back().Node)) {
// TOS has at least one more child so continue DFS
NodeType *childN = *VisitStack.back().second++;
if (!nodeVisitNumbers.count(childN)) {
NodeType *childN = *VisitStack.back().NextChild++;
typename DenseMap<NodeType *, unsigned>::iterator Visited =
nodeVisitNumbers.find(childN);
if (Visited == nodeVisitNumbers.end()) {
// this node has never been seen.
DFSVisitOne(childN);
continue;
}
unsigned childNum = nodeVisitNumbers[childN];
if (MinVisitNumStack.back() > childNum)
MinVisitNumStack.back() = childNum;
unsigned childNum = Visited->second;
if (VisitStack.back().MinVisited > childNum)
VisitStack.back().MinVisited = childNum;
}
}
// Compute the next SCC using the DFS traversal.
void GetNextSCC() {
assert(VisitStack.size() == MinVisitNumStack.size());
CurrentSCC.clear(); // Prepare to compute the next SCC
while (!VisitStack.empty()) {
DFSVisitChildren();
assert(VisitStack.back().second ==
GT::child_end(VisitStack.back().first));
NodeType *visitingN = VisitStack.back().first;
unsigned minVisitNum = MinVisitNumStack.back();
// Pop the leaf on top of the VisitStack.
NodeType *visitingN = VisitStack.back().Node;
unsigned minVisitNum = VisitStack.back().MinVisited;
assert(VisitStack.back().NextChild == GT::child_end(visitingN));
VisitStack.pop_back();
MinVisitNumStack.pop_back();
if (!MinVisitNumStack.empty() && MinVisitNumStack.back() > minVisitNum)
MinVisitNumStack.back() = minVisitNum;
// Propagate MinVisitNum to parent so we can detect the SCC starting node.
if (!VisitStack.empty() && VisitStack.back().MinVisited > minVisitNum)
VisitStack.back().MinVisited = minVisitNum;
#if 0 // Enable if needed when debugging.
dbgs() << "TarjanSCC: Popped node " << visitingN <<