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[DAGCombine] Improve Predecessor check in SimplifySelectOps. NFCI. 

Reuse search space bookkeeping across multiple predecessor checks
qdone to avoid redundancy. This should cut search cost by ~4x.

llvm-svn: 342984
This commit is contained in:
Nirav Dave 2018-09-25 15:29:30 +00:00
parent 7373d5e646
commit f445a67be4
1 changed files with 36 additions and 4 deletions
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40
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -17887,11 +17887,35 @@ bool DAGCombiner::SimplifySelectOps(SDNode *TheSelect, SDValue LHS,
// Check that the select condition doesn't reach either load. If so,
// folding this will induce a cycle into the DAG. If not, this is safe to
// xform, so create a select of the addresses.
SmallPtrSet<const SDNode *, 32> Visited;
SmallVector<const SDNode *, 16> Worklist;
// Always fail if LLD and RLD are not independent. TheSelect is a
// predecessor to all Nodes in question so we need not search past it.
Visited.insert(TheSelect);
Worklist.push_back(LLD);
Worklist.push_back(RLD);
if (SDNode::hasPredecessorHelper(LLD, Visited, Worklist) ||
SDNode::hasPredecessorHelper(RLD, Visited, Worklist))
return false;
SDValue Addr;
if (TheSelect->getOpcode() == ISD::SELECT) {
// We cannot do this optimization if any pair of {RLD, LLD} is a
// predecessor to {RLD, LLD, CondNode}. As we've already compared the
// Loads, we only need to check if CondNode is a successor to one of the
// loads. We can further avoid this if there's no use of their chain
// value.
SDNode *CondNode = TheSelect->getOperand(0).getNode();
if ((LLD->hasAnyUseOfValue(1) && LLD->isPredecessorOf(CondNode)) ||
(RLD->hasAnyUseOfValue(1) && RLD->isPredecessorOf(CondNode)))
Worklist.push_back(CondNode);
if ((LLD->hasAnyUseOfValue(1) &&
SDNode::hasPredecessorHelper(LLD, Visited, Worklist)) ||
(RLD->hasAnyUseOfValue(1) &&
SDNode::hasPredecessorHelper(RLD, Visited, Worklist)))
return false;
Addr = DAG.getSelect(SDLoc(TheSelect),
@ -17899,13 +17923,21 @@ bool DAGCombiner::SimplifySelectOps(SDNode *TheSelect, SDValue LHS,
TheSelect->getOperand(0), LLD->getBasePtr(),
RLD->getBasePtr());
} else { // Otherwise SELECT_CC
// We cannot do this optimization if any pair of {RLD, LLD} is a
// predecessor to {RLD, LLD, CondLHS, CondRHS}. As we've already compared
// the Loads, we only need to check if CondLHS/CondRHS is a successor to
// one of the loads. We can further avoid this if there's no use of their
// chain value.
SDNode *CondLHS = TheSelect->getOperand(0).getNode();
SDNode *CondRHS = TheSelect->getOperand(1).getNode();
Worklist.push_back(CondLHS);
Worklist.push_back(CondRHS);
if ((LLD->hasAnyUseOfValue(1) &&
(LLD->isPredecessorOf(CondLHS) || LLD->isPredecessorOf(CondRHS))) ||
SDNode::hasPredecessorHelper(LLD, Visited, Worklist)) ||
(RLD->hasAnyUseOfValue(1) &&
(RLD->isPredecessorOf(CondLHS) || RLD->isPredecessorOf(CondRHS))))
SDNode::hasPredecessorHelper(RLD, Visited, Worklist)))
return false;
Addr = DAG.getNode(ISD::SELECT_CC, SDLoc(TheSelect),