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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.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234425 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Cameron Zwarich 2015-04-08 18:26:20 +00:00
parent cd13a3808a
commit 011438b1c7
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);
}
}