SmallPtrSet: Reuse DenseMapInfo's pointer hash function instead of inventing a bad one ourselves.

DenseMap's hash function uses slightly more entropy and reduces hash collisions
significantly.  I also experimented with Hashing.h, but it didn't gave a lot of
improvement while being much more expensive to compute.

llvm-svn: 154996

llvm/include/llvm/ADT/SmallPtrSet.h

@@ -126,9 +126,6 @@ protected:
 private:
   bool isSmall() const { return CurArray == SmallArray; }
 
-  unsigned Hash(const void *Ptr) const {
-    return static_cast<unsigned>(((uintptr_t)Ptr >> 4) & (CurArraySize-1));
-  }
   const void * const *FindBucketFor(const void *Ptr) const;
   void shrink_and_clear();
 

llvm/lib/Support/SmallPtrSet.cpp

@@ -13,6 +13,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/Support/MathExtras.h"
 #include <algorithm>
 #include <cstdlib>
@@ -102,7 +103,7 @@ bool SmallPtrSetImpl::erase_imp(const void * Ptr) {
 }
 
 const void * const *SmallPtrSetImpl::FindBucketFor(const void *Ptr) const {
-  unsigned Bucket = Hash(Ptr);
+  unsigned Bucket = DenseMapInfo<void *>::getHashValue(Ptr) & (CurArraySize-1);
   unsigned ArraySize = CurArraySize;
   unsigned ProbeAmt = 1;
   const void *const *Array = CurArray;