Make sure ImmutableSet never inserts Tombstone/Entry into DenseMap.

ImmutAVLTree uses random unsigned values as keys into a DenseMap,
which could possibly happen to be the same value as the Tombstone or
Entry keys in the DenseMap.

Test case is hard to come up with. We randomly get failures on the
internal static analyzer bot, which most likely hits this issue
(hard to be 100% sure without the full stack).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153148 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 2 deletions

diff --git a/include/llvm/ADT/ImmutableSet.h b/include/llvm/ADT/ImmutableSet.h
index 2926462..89b1648 100644
--- a/include/llvm/ADT/ImmutableSet.h
+++ b/include/llvm/ADT/ImmutableSet.h
@@ -347,7 +347,7 @@ public:
       if (prev)
         prev->next = next;
       else
-        factory->Cache[computeDigest()] = next;
+        factory->Cache[factory->maskCacheIndex(computeDigest())] = next;
     }
     
     // We need to clear the mutability bit in case we are
@@ -429,6 +429,11 @@ protected:
   TreeTy*         getRight(TreeTy* T) const { return T->getRight(); }
   value_type_ref  getValue(TreeTy* T) const { return T->value; }
 
+  // Make sure the index is not the Tombstone or Entry key of the DenseMap.
+  static inline unsigned maskCacheIndex(unsigned I) {
+	return (I & ~0x02);
+  }
+
   unsigned incrementHeight(TreeTy* L, TreeTy* R) const {
     unsigned hl = getHeight(L);
     unsigned hr = getHeight(R);
@@ -611,7 +616,7 @@ public:
     // Search the hashtable for another tree with the same digest, and
     // if find a collision compare those trees by their contents.
     unsigned digest = TNew->computeDigest();
-    TreeTy *&entry = Cache[digest];
+    TreeTy *&entry = Cache[maskCacheIndex(digest)];
     do {
       if (!entry)
         break;