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[SelectionDAG] Get rid of recursion in CalcNodeSethiUllmanNumber 

The recursive implementation of CalcNodeSethiUllmanNumber may
overflow stack on extremely long pred chains. This patch replaces it
with an equivalent iterative implementation.

Differential Revision: https://reviews.llvm.org/D33769

llvm-svn: 305775
This commit is contained in:
Max Kazantsev 2017-06-20 07:07:09 +00:00
parent 104b6feb10
commit b5c3362873
1 changed files with 59 additions and 19 deletions
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78
llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
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@ -1861,28 +1861,68 @@ static int checkSpecialNodes(const SUnit *left, const SUnit *right) {
/// Smaller number is the higher priority.
static unsigned
CalcNodeSethiUllmanNumber(const SUnit *SU, std::vector<unsigned> &SUNumbers) {
unsigned &SethiUllmanNumber = SUNumbers[SU->NodeNum];
if (SethiUllmanNumber != 0)
return SethiUllmanNumber;
if (SUNumbers[SU->NodeNum] != 0)
return SUNumbers[SU->NodeNum];
unsigned Extra = 0;
for (const SDep &Pred : SU->Preds) {
if (Pred.isCtrl()) continue; // ignore chain preds
SUnit *PredSU = Pred.getSUnit();
unsigned PredSethiUllman = CalcNodeSethiUllmanNumber(PredSU, SUNumbers);
if (PredSethiUllman > SethiUllmanNumber) {
SethiUllmanNumber = PredSethiUllman;
Extra = 0;
} else if (PredSethiUllman == SethiUllmanNumber)
++Extra;
// Use WorkList to avoid stack overflow on excessively large IRs.
struct WorkState {
WorkState(const SUnit *SU) : SU(SU) {}
const SUnit *SU;
unsigned PredsProcessed = 0;
};
SmallVector<WorkState, 16> WorkList;
WorkList.push_back(SU);
while (!WorkList.empty()) {
auto &Temp = WorkList.back();
auto *TempSU = Temp.SU;
bool AllPredsKnown = true;
// Try to find a non-evaluated pred and push it into the processing stack.
for (unsigned P = Temp.PredsProcessed; P < TempSU->Preds.size(); ++P) {
auto &Pred = TempSU->Preds[P];
if (Pred.isCtrl()) continue; // ignore chain preds
SUnit *PredSU = Pred.getSUnit();
if (SUNumbers[PredSU->NodeNum] == 0) {
#ifndef NDEBUG
// In debug mode, check that we don't have such element in the stack.
for (auto It : WorkList)
assert(It.SU != PredSU && "Trying to push an element twice?");
#endif
WorkList.push_back(PredSU);
AllPredsKnown = false;
// Next time start processing this one starting from the next pred.
Temp.PredsProcessed = P + 1;
break;
}
}
if (!AllPredsKnown)
continue;
// Once all preds are known, we can calculate the answer for this one.
unsigned SethiUllmanNumber = 0;
unsigned Extra = 0;
for (const SDep &Pred : TempSU->Preds) {
if (Pred.isCtrl()) continue; // ignore chain preds
SUnit *PredSU = Pred.getSUnit();
unsigned PredSethiUllman = SUNumbers[PredSU->NodeNum];
assert(PredSethiUllman > 0 && "We should have evaluated this pred!");
if (PredSethiUllman > SethiUllmanNumber) {
SethiUllmanNumber = PredSethiUllman;
Extra = 0;
} else if (PredSethiUllman == SethiUllmanNumber)
++Extra;
}
SethiUllmanNumber += Extra;
if (SethiUllmanNumber == 0)
SethiUllmanNumber = 1;
SUNumbers[TempSU->NodeNum] = SethiUllmanNumber;
WorkList.pop_back();
}
SethiUllmanNumber += Extra;
if (SethiUllmanNumber == 0)
SethiUllmanNumber = 1;
return SethiUllmanNumber;
assert(SUNumbers[SU->NodeNum] > 0 && "SethiUllman should never be zero!");
return SUNumbers[SU->NodeNum];
}
/// CalculateSethiUllmanNumbers - Calculate Sethi-Ullman numbers of all