[DenseMap] Introduce emplace_or_assign (#138886)

Introduce emplace_or_assign, a variant of insert_or_assign that has
slightly better characteristics.

1 files changed, 35 insertions, 0 deletions

diff --git a/llvm/unittests/ADT/DenseMapTest.cpp b/llvm/unittests/ADT/DenseMapTest.cpp
index 2bf0f90..d002a3c 100644
--- a/llvm/unittests/ADT/DenseMapTest.cpp
+++ b/llvm/unittests/ADT/DenseMapTest.cpp
@@ -591,6 +591,41 @@ TEST(DenseMapCustomTest, InsertOrAssignTest) {
   EXPECT_EQ(1, CountCopyAndMove::MoveAssignments);
 }
 
+TEST(DenseMapCustomTest, EmplaceOrAssign) {
+  DenseMap<int, CountCopyAndMove> Map;
+
+  CountCopyAndMove::ResetCounts();
+  auto Try0 = Map.emplace_or_assign(3, 3);
+  EXPECT_TRUE(Try0.second);
+  EXPECT_EQ(0, CountCopyAndMove::TotalCopies());
+  EXPECT_EQ(0, CountCopyAndMove::TotalMoves());
+  EXPECT_EQ(1, CountCopyAndMove::ValueConstructions);
+
+  CountCopyAndMove::ResetCounts();
+  auto Try1 = Map.emplace_or_assign(3, 4);
+  EXPECT_FALSE(Try1.second);
+  EXPECT_EQ(0, CountCopyAndMove::TotalCopies());
+  EXPECT_EQ(1, CountCopyAndMove::ValueConstructions);
+  EXPECT_EQ(0, CountCopyAndMove::MoveConstructions);
+  EXPECT_EQ(1, CountCopyAndMove::MoveAssignments);
+
+  int Key = 5;
+  CountCopyAndMove::ResetCounts();
+  auto Try2 = Map.emplace_or_assign(Key, 3);
+  EXPECT_TRUE(Try2.second);
+  EXPECT_EQ(0, CountCopyAndMove::TotalCopies());
+  EXPECT_EQ(0, CountCopyAndMove::TotalMoves());
+  EXPECT_EQ(1, CountCopyAndMove::ValueConstructions);
+
+  CountCopyAndMove::ResetCounts();
+  auto Try3 = Map.emplace_or_assign(Key, 4);
+  EXPECT_FALSE(Try3.second);
+  EXPECT_EQ(0, CountCopyAndMove::TotalCopies());
+  EXPECT_EQ(1, CountCopyAndMove::ValueConstructions);
+  EXPECT_EQ(0, CountCopyAndMove::MoveConstructions);
+  EXPECT_EQ(1, CountCopyAndMove::MoveAssignments);
+}
+
 // Make sure DenseMap works with StringRef keys.
 TEST(DenseMapCustomTest, StringRefTest) {
   DenseMap<StringRef, int> M;