Merging r322993:

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r322993 | kuhar | 2018-01-19 22:27:24 +0100 (Fri, 19 Jan 2018) | 16 lines

[Dominators] Visit affected node candidates found at different root levels

Summary:
This patch attempts to fix the DomTree incremental insertion bug found here [[ https://bugs.llvm.org/show_bug.cgi?id=35969 | PR35969 ]] .

When performing an insertion into a piece of unreachable CFG, we may find the same not at different levels. When this happens, the node can turn out to be affected when we find it starting from a node with a lower level in the tree. The level at which we start visitation affects if we consider a node affected or not.

This patch tracks the lowest level at which each node was visited during insertion and allows it to be visited multiple times, if it can cause it to be considered affected.

Reviewers: brzycki, davide, dberlin, grosser

Reviewed By: brzycki

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D42231
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_60@323110 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 29 insertions, 9 deletions

diff --git a/include/llvm/Support/GenericDomTreeConstruction.h b/include/llvm/Support/GenericDomTreeConstruction.h
index 8f801662d0f..e85ac76c780 100644
--- a/include/llvm/Support/GenericDomTreeConstruction.h
+++ b/include/llvm/Support/GenericDomTreeConstruction.h
@@ -628,7 +628,7 @@ struct SemiNCAInfo {
         DecreasingLevel>
         Bucket;  // Queue of tree nodes sorted by level in descending order.
     SmallDenseSet<TreeNodePtr, 8> Affected;
-    SmallDenseSet<TreeNodePtr, 8> Visited;
+    SmallDenseMap<TreeNodePtr, unsigned, 8> Visited;
     SmallVector<TreeNodePtr, 8> AffectedQueue;
     SmallVector<TreeNodePtr, 8> VisitedNotAffectedQueue;
   };
@@ -753,14 +753,16 @@ struct SemiNCAInfo {
 
     while (!II.Bucket.empty()) {
       const TreeNodePtr CurrentNode = II.Bucket.top().second;
+      const unsigned  CurrentLevel = CurrentNode->getLevel();
       II.Bucket.pop();
       DEBUG(dbgs() << "\tAdding to Visited and AffectedQueue: "
                    << BlockNamePrinter(CurrentNode) << "\n");
-      II.Visited.insert(CurrentNode);
+
+      II.Visited.insert({CurrentNode, CurrentLevel});
       II.AffectedQueue.push_back(CurrentNode);
 
       // Discover and collect affected successors of the current node.
-      VisitInsertion(DT, BUI, CurrentNode, CurrentNode->getLevel(), NCD, II);
+      VisitInsertion(DT, BUI, CurrentNode, CurrentLevel, NCD, II);
     }
 
     // Finish by updating immediate dominators and levels.
@@ -772,13 +774,17 @@ struct SemiNCAInfo {
                              const TreeNodePtr TN, const unsigned RootLevel,
                              const TreeNodePtr NCD, InsertionInfo &II) {
     const unsigned NCDLevel = NCD->getLevel();
-    DEBUG(dbgs() << "Visiting " << BlockNamePrinter(TN) << "\n");
+    DEBUG(dbgs() << "Visiting " << BlockNamePrinter(TN) << ",  RootLevel "
+                 << RootLevel << "\n");
 
     SmallVector<TreeNodePtr, 8> Stack = {TN};
     assert(TN->getBlock() && II.Visited.count(TN) && "Preconditions!");
 
+    SmallPtrSet<TreeNodePtr, 8> Processed;
+
     do {
       TreeNodePtr Next = Stack.pop_back_val();
+      DEBUG(dbgs() << " Next: " << BlockNamePrinter(Next) << "\n");
 
       for (const NodePtr Succ :
            ChildrenGetter<IsPostDom>::Get(Next->getBlock(), BUI)) {
@@ -786,19 +792,31 @@ struct SemiNCAInfo {
         assert(SuccTN && "Unreachable successor found at reachable insertion");
         const unsigned SuccLevel = SuccTN->getLevel();
 
-        DEBUG(dbgs() << "\tSuccessor " << BlockNamePrinter(Succ)
-                     << ", level = " << SuccLevel << "\n");
+        DEBUG(dbgs() << "\tSuccessor " << BlockNamePrinter(Succ) << ", level = "
+                     << SuccLevel << "\n");
+
+        // Do not process the same node multiple times.
+        if (Processed.count(Next) > 0)
+          continue;
 
         // Succ dominated by subtree From -- not affected.
         // (Based on the lemma 2.5 from the second paper.)
         if (SuccLevel > RootLevel) {
           DEBUG(dbgs() << "\t\tDominated by subtree From\n");
-          if (II.Visited.count(SuccTN) != 0)
-            continue;
+          if (II.Visited.count(SuccTN) != 0) {
+            DEBUG(dbgs() << "\t\t\talready visited at level "
+                         << II.Visited[SuccTN] << "\n\t\t\tcurrent level "
+                         << RootLevel << ")\n");
+
+            // A node can be necessary to visit again if we see it again at
+            // a lower level than before.
+            if (II.Visited[SuccTN] >= RootLevel)
+              continue;
+          }
 
           DEBUG(dbgs() << "\t\tMarking visited not affected "
                        << BlockNamePrinter(Succ) << "\n");
-          II.Visited.insert(SuccTN);
+          II.Visited.insert({SuccTN, RootLevel});
           II.VisitedNotAffectedQueue.push_back(SuccTN);
           Stack.push_back(SuccTN);
         } else if ((SuccLevel > NCDLevel + 1) &&
@@ -809,6 +827,8 @@ struct SemiNCAInfo {
           II.Bucket.push({SuccLevel, SuccTN});
         }
       }
+
+      Processed.insert(Next);
     } while (!Stack.empty());
   }