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SchedDFS: Refactor and tweak the subtree selection criteria.

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For sanity, create a root when NumDataSuccs >= 4. Splitting large
subtrees will no longer be detrimental after my next checkin to handle
nested tree. A magic number of 4 is fine because single subtrees
seldom rejoin more than this. It makes subtrees easier to visualize
and heuristics more sane.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173399 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick 2013-01-25 00:12:57 +00:00
parent 6d28299b9d
commit b12a771992
1 changed files with 32 additions and 24 deletions
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56
lib/CodeGen/ScheduleDAGInstrs.cpp
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@ -1039,37 +1039,17 @@ public:
void visitPostorder(const SUnit *SU, const SDep *PredDep, const SUnit *Parent) {
R.DFSData[SU->NodeNum].SubtreeID = SU->NodeNum;
// Join the child to its parent if they are connected via data dependence
// and do not exceed the limit.
if (!Parent || PredDep->getKind() != SDep::Data)
if (!Parent)
return;
assert(PredDep && "PredDep required for non-root node");
unsigned PredCnt = R.DFSData[SU->NodeNum].InstrCount;
if (PredCnt > R.SubtreeLimit)
return;
R.DFSData[SU->NodeNum].SubtreeID = Parent->NodeNum;
// Add the recently finished predecessor's bottom-up descendent count.
R.DFSData[Parent->NodeNum].InstrCount += PredCnt;
SubtreeClasses.join(Parent->NodeNum, SU->NodeNum);
joinPredSubtree(*PredDep, Parent);
}
/// Determine whether the DFS cross edge should be considered a subtree edge
/// or a connection between subtrees.
void visitCross(const SDep &PredDep, const SUnit *Succ) {
if (PredDep.getKind() == SDep::Data) {
// If this is a cross edge to a root, join the subtrees. This happens when
// the root was first reached by a non-data dependence.
unsigned NodeNum = PredDep.getSUnit()->NodeNum;
unsigned PredCnt = R.DFSData[NodeNum].InstrCount;
if (R.DFSData[NodeNum].SubtreeID == NodeNum && PredCnt < R.SubtreeLimit) {
R.DFSData[NodeNum].SubtreeID = Succ->NodeNum;
R.DFSData[Succ->NodeNum].InstrCount += PredCnt;
SubtreeClasses.join(Succ->NodeNum, NodeNum);
return;
}
}
joinPredSubtree(PredDep, Succ);
ConnectionPairs.push_back(std::make_pair(PredDep.getSUnit(), Succ));
}
@ -1099,6 +1079,34 @@ public:
}
protected:
void joinPredSubtree(const SDep &PredDep, const SUnit *Succ) {
// Join the child to its parent if they are connected via data dependence.
if (PredDep.getKind() != SDep::Data)
return;
// Four is the magic number of successors before a node is considered a
// pinch point.
unsigned NumDataSucs = 0;
const SUnit *PredSU = PredDep.getSUnit();
for (SUnit::const_succ_iterator SI = PredSU->Succs.begin(),
SE = PredSU->Succs.end(); SI != SE; ++SI) {
if (SI->getKind() == SDep::Data) {
if (++NumDataSucs >= 4)
return;
}
}
// If this is a cross edge to a root, join the subtrees. This happens when
// the root was first reached by a non-data dependence.
unsigned NodeNum = PredSU->NodeNum;
unsigned PredCnt = R.DFSData[NodeNum].InstrCount;
if (R.DFSData[NodeNum].SubtreeID == NodeNum && PredCnt < R.SubtreeLimit) {
R.DFSData[NodeNum].SubtreeID = Succ->NodeNum;
R.DFSData[Succ->NodeNum].InstrCount += PredCnt;
SubtreeClasses.join(Succ->NodeNum, NodeNum);
return;
}
}
/// Called by finalize() to record a connection between trees.
void addConnection(unsigned FromTree, unsigned ToTree, unsigned Depth) {
if (!Depth)