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Eliminate O(n^2) worst-case behavior in SSA construction

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The code uses a priority queue and a worklist, which share the same
visited set, but the visited set is only updated when inserting into
the priority queue. Instead, switch to using separate visited sets
for the priority queue and worklist.

llvm-svn: 234425
This commit is contained in:
Cameron Zwarich 2015-04-08 18:26:20 +00:00
parent 23b1ef3354
commit f48f486c1d
1 changed files with 6 additions and 3 deletions
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9
lib/Transforms/Utils/PromoteMemoryToRegister.cpp
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@ -872,8 +872,10 @@ void PromoteMem2Reg::DetermineInsertionPoint(AllocaInst *AI, unsigned AllocaNum,
}
SmallVector<std::pair<unsigned, BasicBlock *>, 32> DFBlocks;
SmallPtrSet<DomTreeNode *, 32> Visited;
SmallVector<DomTreeNode *, 32> Worklist;
SmallPtrSet<DomTreeNode *, 32> VisitedPQ;
SmallPtrSet<DomTreeNode *, 32> VisitedWorklist;
while (!PQ.empty()) {
DomTreeNodePair RootPair = PQ.top();
PQ.pop();
@ -887,6 +889,7 @@ void PromoteMem2Reg::DetermineInsertionPoint(AllocaInst *AI, unsigned AllocaNum,
Worklist.clear();
Worklist.push_back(Root);
VisitedWorklist.insert(Root);
while (!Worklist.empty()) {
DomTreeNode *Node = Worklist.pop_back_val();
@ -905,7 +908,7 @@ void PromoteMem2Reg::DetermineInsertionPoint(AllocaInst *AI, unsigned AllocaNum,
if (SuccLevel > RootLevel)
continue;
if (!Visited.insert(SuccNode).second)
if (!VisitedPQ.insert(SuccNode).second)
continue;
BasicBlock *SuccBB = SuccNode->getBlock();
@ -919,7 +922,7 @@ void PromoteMem2Reg::DetermineInsertionPoint(AllocaInst *AI, unsigned AllocaNum,
for (DomTreeNode::iterator CI = Node->begin(), CE = Node->end(); CI != CE;
++CI) {
if (!Visited.count(*CI))
if (VisitedWorklist.insert(*CI).second)
Worklist.push_back(*CI);
}
}