[objc-arc] Track if we encountered an additive overflow while computing {TopDown,BottomUp}PathCounts and do nothing if it occurred.

I fixed the aforementioned problems that came up on some of the linux boxes.
Major thanks to Nick Lewycky for his help debugging!

rdar://14590914

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188122 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/ObjCARC/ObjCARCOpts.cpp

@@ -674,7 +674,9 @@ namespace {
     SmallVector<BasicBlock *, 2> Succs;
 
   public:
-    BBState() : TopDownPathCount(0), BottomUpPathCount(0) {}
+    static const unsigned OverflowOccurredValue;
+
+    BBState() : TopDownPathCount(0), BottomUpPathCount(0) { }
 
     typedef MapTy::iterator ptr_iterator;
     typedef MapTy::const_iterator ptr_const_iterator;
@@ -745,13 +747,15 @@ namespace {
     /// Returns true if overflow occured. Returns false if overflow did not
     /// occur.
     bool GetAllPathCountWithOverflow(unsigned &PathCount) const {
-      assert(TopDownPathCount != 0);
-      assert(BottomUpPathCount != 0);
+      if (TopDownPathCount == OverflowOccurredValue ||
+          BottomUpPathCount == OverflowOccurredValue)
+        return true;
       unsigned long long Product =
         (unsigned long long)TopDownPathCount*BottomUpPathCount;
-      PathCount = Product;
-      // Overflow occured if any of the upper bits of Product are set.
-      return Product >> 32;
+      // Overflow occured if any of the upper bits of Product are set or if all
+      // the lower bits of Product are all set.
+      return (Product >> 32) ||
+             ((PathCount = Product) == OverflowOccurredValue);
     }
 
     // Specialized CFG utilities.
@@ -766,6 +770,8 @@ namespace {
 
     bool isExit() const { return Succs.empty(); }
   };
+
+  const unsigned BBState::OverflowOccurredValue = 0xffffffff;
 }
 
 void BBState::InitFromPred(const BBState &Other) {
@@ -781,13 +787,25 @@ void BBState::InitFromSucc(const BBState &Other) {
 /// The top-down traversal uses this to merge information about predecessors to
 /// form the initial state for a new block.
 void BBState::MergePred(const BBState &Other) {
+  if (TopDownPathCount == OverflowOccurredValue)
+    return;
+
   // Other.TopDownPathCount can be 0, in which case it is either dead or a
   // loop backedge. Loop backedges are special.
   TopDownPathCount += Other.TopDownPathCount;
 
+  // In order to be consistent, we clear the top down pointers when by adding
+  // TopDownPathCount becomes OverflowOccurredValue even though "true" overflow
+  // has not occured.
+  if (TopDownPathCount == OverflowOccurredValue) {
+    clearTopDownPointers();
+    return;
+  }
+
   // Check for overflow. If we have overflow, fall back to conservative
   // behavior.
   if (TopDownPathCount < Other.TopDownPathCount) {
+    TopDownPathCount = OverflowOccurredValue;
     clearTopDownPointers();
     return;
   }
@@ -813,13 +831,25 @@ void BBState::MergePred(const BBState &Other) {
 /// The bottom-up traversal uses this to merge information about successors to
 /// form the initial state for a new block.
 void BBState::MergeSucc(const BBState &Other) {
+  if (BottomUpPathCount == OverflowOccurredValue)
+    return;
+
   // Other.BottomUpPathCount can be 0, in which case it is either dead or a
   // loop backedge. Loop backedges are special.
   BottomUpPathCount += Other.BottomUpPathCount;
 
+  // In order to be consistent, we clear the top down pointers when by adding
+  // BottomUpPathCount becomes OverflowOccurredValue even though "true" overflow
+  // has not occured.
+  if (BottomUpPathCount == OverflowOccurredValue) {
+    clearBottomUpPointers();
+    return;
+  }
+
   // Check for overflow. If we have overflow, fall back to conservative
   // behavior.
   if (BottomUpPathCount < Other.BottomUpPathCount) {
+    BottomUpPathCount = OverflowOccurredValue;
     clearBottomUpPointers();
     return;
   }
@@ -2526,9 +2556,12 @@ ObjCARCOpt::ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState>
           // If we overflow when we compute the path count, don't remove/move
           // anything.
           const BBState &NRRBBState = BBStates[NewRetainRelease->getParent()];
-          unsigned PathCount;
+          unsigned PathCount = BBState::OverflowOccurredValue;
           if (NRRBBState.GetAllPathCountWithOverflow(PathCount))
             return false;
+          assert(PathCount != BBState::OverflowOccurredValue &&
+                 "PathCount at this point can not be "
+                 "OverflowOccurredValue.");
           OldDelta -= PathCount;
 
           // Merge the ReleaseMetadata and IsTailCallRelease values.
@@ -2558,8 +2591,12 @@ ObjCARCOpt::ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState>
                 // If we overflow when we compute the path count, don't
                 // remove/move anything.
                 const BBState &RIPBBState = BBStates[RIP->getParent()];
+                PathCount = BBState::OverflowOccurredValue;
                 if (RIPBBState.GetAllPathCountWithOverflow(PathCount))
                   return false;
+                assert(PathCount != BBState::OverflowOccurredValue &&
+                       "PathCount at this point can not be "
+                       "OverflowOccurredValue.");
                 NewDelta -= PathCount;
               }
             }
@@ -2595,9 +2632,12 @@ ObjCARCOpt::ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState>
           // If we overflow when we compute the path count, don't remove/move
           // anything.
           const BBState &NRRBBState = BBStates[NewReleaseRetain->getParent()];
-          unsigned PathCount;
+          unsigned PathCount = BBState::OverflowOccurredValue;
           if (NRRBBState.GetAllPathCountWithOverflow(PathCount))
             return false;
+          assert(PathCount != BBState::OverflowOccurredValue &&
+                 "PathCount at this point can not be "
+                 "OverflowOccurredValue.");
           OldDelta += PathCount;
           OldCount += PathCount;
 
@@ -2612,8 +2652,13 @@ ObjCARCOpt::ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState>
                 // If we overflow when we compute the path count, don't
                 // remove/move anything.
                 const BBState &RIPBBState = BBStates[RIP->getParent()];
+
+                PathCount = BBState::OverflowOccurredValue;
                 if (RIPBBState.GetAllPathCountWithOverflow(PathCount))
                   return false;
+                assert(PathCount != BBState::OverflowOccurredValue &&
+                       "PathCount at this point can not be "
+                       "OverflowOccurredValue.");
                 NewDelta += PathCount;
                 NewCount += PathCount;
               }