[PATCH] D18154: DenseMap: make .resize() do the intuitive thing

[escha via llvm-commits]

escha updated this revision to Diff 50637.
escha added a comment.

Added a test to make sure that resizing is enough to insert N elements without reallocation for a variety of sizes.

I also looked quickly over the uses and none of the uses seem to be already-compensating for this.


Repository:
  rL LLVM

http://reviews.llvm.org/D18154

Files:
  include/llvm/ADT/DenseMap.h
  unittests/ADT/DenseMapTest.cpp

Index: unittests/ADT/DenseMapTest.cpp
===================================================================
--- unittests/ADT/DenseMapTest.cpp
+++ unittests/ADT/DenseMapTest.cpp
@@ -339,6 +339,19 @@
   EXPECT_TRUE(cit == cit2);
 }
 
+// Make sure resize actually gives us enough buckets to insert N items
+// without increasing allocation size.
+TEST(DenseMapCustomTest, ResizeTest) {
+  for (unsigned Size = 16; Size < 32; ++Size) {
+    DenseMap<unsigned, unsigned> Map;
+    Map.resize(Size);
+    unsigned MemorySize = Map.getMemorySize();
+    for (unsigned i = 0; i < Size; ++i)
+      Map[i] = i;
+    EXPECT_TRUE(Map.getMemorySize() == MemorySize);
+  }
+}
+
 // Make sure DenseMap works with StringRef keys.
 TEST(DenseMapCustomTest, StringRefTest) {
   DenseMap<StringRef, int> M;
Index: include/llvm/ADT/DenseMap.h
===================================================================
--- include/llvm/ADT/DenseMap.h
+++ include/llvm/ADT/DenseMap.h
@@ -81,8 +81,12 @@
   }
   unsigned size() const { return getNumEntries(); }
 
-  /// Grow the densemap so that it has at least Size buckets. Does not shrink
+  /// Grow the densemap so that it can contain at least Size items before
+  /// resizing again. This means somewhat more than Size buckets because
+  /// densemap resizes upon reaching 3/4 full.
   void resize(size_type Size) {
+    // Size *= (4/3), rounding up.
+    Size = (Size * 4 + 2) / 3;
     incrementEpoch();
     if (Size > getNumBuckets())
       grow(Size);


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