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Some improvements related to the computation of heights, depths of SUnits.

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The basic idea is that all these algorithms are computing the longest paths from the root node or to the exit node. Therefore the existing implementation that uses and iterative and potentially
exponential algorithm was changed to a well-known graph algorithm based on dynamic programming. It has a linear run-time.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47884 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Roman Levenstein 2008-03-04 11:19:43 +00:00
parent ef12057737
commit d86449e774
1 changed files with 93 additions and 21 deletions
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114
lib/CodeGen/SelectionDAG/ScheduleDAG.cpp
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@ -232,39 +232,111 @@ void ScheduleDAG::ComputeLatency(SUnit *SU) {
}
}
/// CalculateDepths - compute depths using algorithms for the longest
/// paths in the DAG
void ScheduleDAG::CalculateDepths() {
std::vector<std::pair<SUnit*, unsigned> > WorkList;
for (unsigned i = 0, e = SUnits.size(); i != e; ++i)
if (SUnits[i].Preds.empty())
WorkList.push_back(std::make_pair(&SUnits[i], 0U));
unsigned DAGSize = SUnits.size();
std::vector<unsigned> InDegree(DAGSize);
std::vector<SUnit*> WorkList;
WorkList.reserve(DAGSize);
// Initialize the data structures
for (unsigned i = 0, e = DAGSize; i != e; ++i) {
SUnit *SU = &SUnits[i];
int NodeNum = SU->NodeNum;
unsigned Degree = SU->Preds.size();
InDegree[NodeNum] = Degree;
SU->Depth = 0;
// Is it a node without dependencies?
if (Degree == 0) {
assert(SU->Preds.empty() && "SUnit should have no predecessors");
// Collect leaf nodes
WorkList.push_back(SU);
}
}
// Process nodes in the topological order
while (!WorkList.empty()) {
SUnit *SU = WorkList.back().first;
unsigned Depth = WorkList.back().second;
SUnit *SU = WorkList.back();
WorkList.pop_back();
if (SU->Depth == 0 || Depth > SU->Depth) {
SU->Depth = Depth;
for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
I != E; ++I)
WorkList.push_back(std::make_pair(I->Dep, Depth+1));
unsigned &SUDepth = SU->Depth;
// Use dynamic programming:
// When current node is being processed, all of its dependencies
// are already processed.
// So, just iterate over all predecessors and take the longest path
for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
I != E; ++I) {
unsigned PredDepth = I->Dep->Depth;
if (PredDepth+1 > SUDepth) {
SUDepth = PredDepth + 1;
}
}
// Update InDegrees of all nodes depending on current SUnit
for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
I != E; ++I) {
SUnit *SU = I->Dep;
if (!--InDegree[SU->NodeNum])
// If all dependencies of the node are processed already,
// then the longest path for the node can be computed now
WorkList.push_back(SU);
}
}
}
/// CalculateHeights - compute heights using algorithms for the longest
/// paths in the DAG
void ScheduleDAG::CalculateHeights() {
std::vector<std::pair<SUnit*, unsigned> > WorkList;
SUnit *Root = SUnitMap[DAG.getRoot().Val].front();
WorkList.push_back(std::make_pair(Root, 0U));
unsigned DAGSize = SUnits.size();
std::vector<unsigned> InDegree(DAGSize);
std::vector<SUnit*> WorkList;
WorkList.reserve(DAGSize);
// Initialize the data structures
for (unsigned i = 0, e = DAGSize; i != e; ++i) {
SUnit *SU = &SUnits[i];
int NodeNum = SU->NodeNum;
unsigned Degree = SU->Succs.size();
InDegree[NodeNum] = Degree;
SU->Height = 0;
// Is it a node without dependencies?
if (Degree == 0) {
assert(SU->Succs.empty() && "Something wrong");
assert(WorkList.empty() && "Should be empty");
// Collect leaf nodes
WorkList.push_back(SU);
}
}
// Process nodes in the topological order
while (!WorkList.empty()) {
SUnit *SU = WorkList.back().first;
unsigned Height = WorkList.back().second;
SUnit *SU = WorkList.back();
WorkList.pop_back();
if (SU->Height == 0 || Height > SU->Height) {
SU->Height = Height;
for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
I != E; ++I)
WorkList.push_back(std::make_pair(I->Dep, Height+1));
unsigned &SUHeight = SU->Height;
// Use dynamic programming:
// When current node is being processed, all of its dependencies
// are already processed.
// So, just iterate over all successors and take the longest path
for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
I != E; ++I) {
unsigned SuccHeight = I->Dep->Height;
if (SuccHeight+1 > SUHeight) {
SUHeight = SuccHeight + 1;
}
}
// Update InDegrees of all nodes depending on current SUnit
for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
I != E; ++I) {
SUnit *SU = I->Dep;
if (!--InDegree[SU->NodeNum])
// If all dependencies of the node are processed already,
// then the longest path for the node can be computed now
WorkList.push_back(SU);
}
}
}