[LLVMdev] [PATCH 3/5] Prevent infinite growth of SmallPtrSet instances.

jfonseca at vmware.com
2011-03-15T23:15:53Z

From: José Fonseca <jfonseca at vmware.com>

Rehash but don't grow when full of tombstones.
---
 include/llvm/ADT/SmallPtrSet.h |    2 +-
 lib/Support/SmallPtrSet.cpp    |   15 +++++++++------
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/include/llvm/ADT/SmallPtrSet.h b/include/llvm/ADT/SmallPtrSet.h
index ff32ba8..9992858 100644
--- a/include/llvm/ADT/SmallPtrSet.h
+++ b/include/llvm/ADT/SmallPtrSet.h
@@ -133,7 +133,7 @@ private:
   void shrink_and_clear();

   /// Grow - Allocate a larger backing store for the buckets and move it over.
-  void Grow();
+  void Grow(unsigned NewSize);

   void operator=(const SmallPtrSetImpl &RHS);  // DO NOT IMPLEMENT.
 protected:
diff --git a/lib/Support/SmallPtrSet.cpp b/lib/Support/SmallPtrSet.cpp
index 504e649..997ce0b 100644
--- a/lib/Support/SmallPtrSet.cpp
+++ b/lib/Support/SmallPtrSet.cpp
@@ -52,10 +52,14 @@ bool SmallPtrSetImpl::insert_imp(const void * Ptr) {
     // Otherwise, hit the big set case, which will call grow.
   }

-  // If more than 3/4 of the array is full, grow.
-  if (NumElements*4 >= CurArraySize*3 ||
-      CurArraySize-(NumElements+NumTombstones) < CurArraySize/8)
-    Grow();
+  if (NumElements*4 >= CurArraySize*3) {
+    // If more than 3/4 of the array is full, grow.
+    Grow(CurArraySize < 64 ? 128 : CurArraySize*2);
+  } else if (CurArraySize-(NumElements+NumTombstones) < CurArraySize/8) {
+    // If fewer of 1/8 of the array is empty (meaning that many are filled with
+    // tombstones), rehash.
+    Grow(CurArraySize);
+  }

   // Okay, we know we have space.  Find a hash bucket.
   const void **Bucket = const_cast<const void**>(FindBucketFor(Ptr));
@@ -125,10 +129,9 @@ const void * const *SmallPtrSetImpl::FindBucketFor(const
void *Ptr) const {

 /// Grow - Allocate a larger backing store for the buckets and move it over.
 ///
-void SmallPtrSetImpl::Grow() {
+void SmallPtrSetImpl::Grow(unsigned NewSize) {
   // Allocate at twice as many buckets, but at least 128.
   unsigned OldSize = CurArraySize;
-  unsigned NewSize = OldSize < 64 ? 128 : OldSize*2;

   const void **OldBuckets = CurArray;
   bool WasSmall = isSmall();
--
1.7.4.1