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

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

1 files changed, 6 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp b/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
index 4b34b193773..54e1733c3f6 100644
--- a/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
+++ b/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
@@ -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);
       }
     }