Prevent infinite growth of SmallMap instances.

Rehash but don't grow when full of tombstones.

Patch by José Fonseca!

llvm-svn: 128565

1 files changed, 13 insertions, 1 deletions

diff --git a/llvm/lib/Support/StringMap.cpp b/llvm/lib/Support/StringMap.cpp
index 90ec2995026..f193aa42a44 100644
--- a/llvm/lib/Support/StringMap.cpp
+++ b/llvm/lib/Support/StringMap.cpp
@@ -177,7 +177,19 @@ StringMapEntryBase *StringMapImpl::RemoveKey(StringRef Key) {
 /// RehashTable - Grow the table, redistributing values into the buckets with
 /// the appropriate mod-of-hashtable-size.
 void StringMapImpl::RehashTable() {
-  unsigned NewSize = NumBuckets*2;
+  unsigned NewSize;
+
+  // If the hash table is now more than 3/4 full, or if fewer than 1/8 of
+  // the buckets are empty (meaning that many are filled with tombstones),
+  // grow/rehash the table.
+  if (NumItems*4 > NumBuckets*3) {
+    NewSize = NumBuckets*2;
+  } else if (NumBuckets-(NumItems+NumTombstones) < NumBuckets/8) {
+    NewSize = NumBuckets;
+  } else {
+    return;
+  }
+
   // Allocate one extra bucket which will always be non-empty.  This allows the
   // iterators to stop at end.
   ItemBucket *NewTableArray =(ItemBucket*)calloc(NewSize+1, sizeof(ItemBucket));