[PATCH] D16671: SmallPtrSet: Only initialize NumTombstones when not small anymore.

[Matthias Braun via llvm-commits]

MatzeB created this revision.
MatzeB added reviewers: dblaikie, chandlerc, reames, bkramer.
MatzeB added a subscriber: llvm-commits.
MatzeB set the repository for this revision to rL LLVM.
Herald added a subscriber: mcrosier.

SmallPtrSets stay small in the majority of cases so this is just another
memory operation that can be avoid in the common case.

Repository:
  rL LLVM

http://reviews.llvm.org/D16671

Files:
  include/llvm/ADT/SmallPtrSet.h
  lib/Support/SmallPtrSet.cpp

Index: lib/Support/SmallPtrSet.cpp
===================================================================
--- lib/Support/SmallPtrSet.cpp
+++ lib/Support/SmallPtrSet.cpp
@@ -39,11 +39,14 @@
   if (LLVM_UNLIKELY(NumElements * 4 >= CurArraySize * 3)) {
     // If more than 3/4 of the array is full, grow.
     Grow(CurArraySize < 64 ? 128 : CurArraySize*2);
-  } else if (LLVM_UNLIKELY(CurArraySize - (NumElements + NumTombstones) <
+  } else {
+    assert(!isSmall() && "NumTombstones is uninitialized if not small");
+    if (LLVM_UNLIKELY(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);
+      // 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.
@@ -147,8 +150,8 @@
     }
 
     free(OldBuckets);
-    NumTombstones = 0;
   }
+  NumTombstones = 0;
 }
 
 SmallPtrSetImplBase::SmallPtrSetImplBase(const void **SmallStorage,
@@ -212,7 +215,8 @@
   memcpy(CurArray, RHS.CurArray, sizeof(void*)*CurArraySize);
 
   NumElements = RHS.NumElements;
-  NumTombstones = RHS.NumTombstones;
+  if (!RHS.isSmall())
+    NumTombstones = RHS.NumTombstones;
 }
 
 void SmallPtrSetImplBase::MoveFrom(unsigned SmallSize,
@@ -233,18 +237,17 @@
   } else {
     CurArray = RHS.CurArray;
     RHS.CurArray = RHS.SmallArray;
+    NumTombstones = RHS.NumTombstones;
   }
 
   // Copy the rest of the trivial members.
   CurArraySize = RHS.CurArraySize;
   NumElements = RHS.NumElements;
-  NumTombstones = RHS.NumTombstones;
 
   // Make the RHS small and empty.
   RHS.CurArraySize = SmallSize;
   assert(RHS.CurArray == RHS.SmallArray);
   RHS.NumElements = 0;
-  RHS.NumTombstones = 0;
 }
 
 void SmallPtrSetImplBase::swap(SmallPtrSetImplBase &RHS) {
@@ -271,7 +274,6 @@
     RHS.CurArray = this->CurArray;
     RHS.NumTombstones = this->NumTombstones;
     this->CurArray = this->SmallArray;
-    this->NumTombstones = 0;
     return;
   }
 
@@ -283,7 +285,6 @@
     std::swap(RHS.NumElements, this->NumElements);
     std::swap(RHS.CurArraySize, this->CurArraySize);
     this->CurArray = RHS.CurArray;
-    this->NumTombstones = RHS.NumTombstones;
     RHS.CurArray = RHS.SmallArray;
     RHS.NumTombstones = 0;
     return;
Index: include/llvm/ADT/SmallPtrSet.h
===================================================================
--- include/llvm/ADT/SmallPtrSet.h
+++ include/llvm/ADT/SmallPtrSet.h
@@ -60,6 +60,7 @@
 
   // If small, this is # elts allocated consecutively
   unsigned NumElements;
+  /// Uninitialized for small sets, otherwise the number of tombstones.
   unsigned NumTombstones;
 
   // Helpers to copy and move construct a SmallPtrSet.
@@ -92,7 +93,6 @@
     // Fill the array with empty markers.
     memset(CurArray, -1, CurArraySize*sizeof(void*));
     NumElements = 0;
-    NumTombstones = 0;
   }
 
 protected:


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