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Optimize SelectionDAG's topological sort to use one pass instead

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of two, and to not need a scratch std::vector. Also, use the
SelectionDAG's topological sort in LegalizeDAG instead of having
a separate implementation.

llvm-svn: 55389
This commit is contained in:
Dan Gohman 2008-08-26 21:42:18 +00:00
parent 57b5f9b931
commit 3e50c6348a
2 changed files with 12 additions and 56 deletions
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49
lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
View File

@ -270,45 +270,6 @@ SelectionDAGLegalize::SelectionDAGLegalize(SelectionDAG &dag)
"Too many value types for ValueTypeActions to hold!");
}
/// ComputeTopDownOrdering - Compute a top-down ordering of the dag, where Order
/// contains all of a nodes operands before it contains the node.
static void ComputeTopDownOrdering(SelectionDAG &DAG,
SmallVector<SDNode*, 64> &Order) {
DenseMap<SDNode*, unsigned> Visited;
std::vector<SDNode*> Worklist;
Worklist.reserve(128);
// Compute ordering from all of the leaves in the graphs, those (like the
// entry node) that have no operands.
for (SelectionDAG::allnodes_iterator I = DAG.allnodes_begin(),
E = DAG.allnodes_end(); I != E; ++I) {
if (I->getNumOperands() == 0) {
Visited[I] = 0 - 1U;
Worklist.push_back(I);
}
}
while (!Worklist.empty()) {
SDNode *N = Worklist.back();
Worklist.pop_back();
if (++Visited[N] != N->getNumOperands())
continue; // Haven't visited all operands yet
Order.push_back(N);
// Now that we have N in, add anything that uses it if all of their operands
// are now done.
Worklist.insert(Worklist.end(), N->use_begin(), N->use_end());
}
assert(Order.size() == Visited.size() &&
Order.size() == DAG.allnodes_size() &&
"Error: DAG is cyclic!");
}
void SelectionDAGLegalize::LegalizeDAG() {
LastCALLSEQ_END = DAG.getEntryNode();
IsLegalizingCall = false;
@ -319,11 +280,11 @@ void SelectionDAGLegalize::LegalizeDAG() {
// practice however, this causes us to run out of stack space on large basic
// blocks. To avoid this problem, compute an ordering of the nodes where each
// node is only legalized after all of its operands are legalized.
SmallVector<SDNode*, 64> Order;
ComputeTopDownOrdering(DAG, Order);
for (unsigned i = 0, e = Order.size(); i != e; ++i)
HandleOp(SDValue(Order[i], 0));
std::vector<SDNode *> TopOrder;
unsigned N = DAG.AssignTopologicalOrder(TopOrder);
for (unsigned i = N; i != 0; --i)
HandleOp(SDValue(TopOrder[i-1], 0));
TopOrder.clear();
// Finally, it's possible the root changed. Get the new root.
SDValue OldRoot = DAG.getRoot();

19
lib/CodeGen/SelectionDAG/SelectionDAG.cpp
View File

@ -4427,40 +4427,35 @@ void SelectionDAG::ReplaceAllUsesOfValuesWith(const SDValue *From,
/// of the SDNodes* in assigned order by reference.
unsigned SelectionDAG::AssignTopologicalOrder(std::vector<SDNode*> &TopOrder) {
unsigned DAGSize = AllNodes.size();
std::vector<unsigned> InDegree(DAGSize);
std::vector<SDNode*> Sources;
// Use a two pass approach to avoid using a std::map which is slow.
unsigned Id = 0;
for (allnodes_iterator I = allnodes_begin(),E = allnodes_end(); I != E; ++I){
SDNode *N = I;
N->setNodeId(Id++);
unsigned Degree = N->use_size();
InDegree[N->getNodeId()] = Degree;
// Temporarily use the Node Id as scratch space for the degree count.
N->setNodeId(Degree);
if (Degree == 0)
Sources.push_back(N);
}
TopOrder.clear();
TopOrder.reserve(DAGSize);
int Id = 0;
while (!Sources.empty()) {
SDNode *N = Sources.back();
Sources.pop_back();
TopOrder.push_back(N);
N->setNodeId(Id++);
for (SDNode::op_iterator I = N->op_begin(), E = N->op_end(); I != E; ++I) {
SDNode *P = I->getVal();
unsigned Degree = --InDegree[P->getNodeId()];
unsigned Degree = P->getNodeId();
--Degree;
P->setNodeId(Degree);
if (Degree == 0)
Sources.push_back(P);
}
}
// Second pass, assign the actual topological order as node ids.
Id = 0;
for (std::vector<SDNode*>::iterator TI = TopOrder.begin(),TE = TopOrder.end();
TI != TE; ++TI)
(*TI)->setNodeId(Id++);
return Id;
}