Fix PR13148, an inf-loop in StringMap.

StringMap suffered from the same bug as DenseMap: when you explicitly
construct it with a small number of buckets, you can arrange for the
tombstone-based growth path to be followed when the number of buckets
was less than '8'. In that case, even with a full map, it would compare
'0' as not less than '0', and refuse to grow the table, leading to
inf-loops trying to find an empty bucket on the next insertion. The fix
is very simple: use '<=' as the comparison. The same fix was applied to
DenseMap as well during its recent refactoring.

Thanks to Alex Bolz for the great report and test case. =]

llvm-svn: 158725

1 files changed, 22 insertions, 0 deletions

diff --git a/llvm/unittests/ADT/StringMapTest.cpp b/llvm/unittests/ADT/StringMapTest.cpp
index 66e04933adf..5bb65cbd7aa 100644
--- a/llvm/unittests/ADT/StringMapTest.cpp
+++ b/llvm/unittests/ADT/StringMapTest.cpp
@@ -134,6 +134,28 @@ TEST_F(StringMapTest, InsertAndEraseTest) {
   assertSingleItemMap();
 }
 
+TEST_F(StringMapTest, SmallFullMapTest) {
+  // StringMap has a tricky corner case when the map is small (<8 buckets) and
+  // it fills up through a balanced pattern of inserts and erases. This can
+  // lead to inf-loops in some cases (PR13148) so we test it explicitly here.
+  llvm::StringMap<int> Map(2);
+
+  Map["eins"] = 1;
+  Map["zwei"] = 2;
+  Map["drei"] = 3;
+  Map.erase("drei");
+  Map.erase("eins");
+  Map["veir"] = 4;
+  Map["funf"] = 5;
+
+  EXPECT_EQ(3u, Map.size());
+  EXPECT_EQ(0, Map.lookup("eins"));
+  EXPECT_EQ(2, Map.lookup("zwei"));
+  EXPECT_EQ(0, Map.lookup("drei"));
+  EXPECT_EQ(4, Map.lookup("veir"));
+  EXPECT_EQ(5, Map.lookup("funf"));
+}
+
 // A more complex iteration test.
 TEST_F(StringMapTest, IterationTest) {
   bool visited[100];