StringMap/DenseMap unittests: use piecewise_construct and ensure no copy occurs.

This makes us no longer relying on move-construction elision by the compiler.
Suggested by D. Blaikie.

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 264475

1 files changed, 6 insertions, 11 deletions

diff --git a/llvm/unittests/ADT/StringMapTest.cpp b/llvm/unittests/ADT/StringMapTest.cpp
index 4deb48c..562126e 100644
--- a/llvm/unittests/ADT/StringMapTest.cpp
+++ b/llvm/unittests/ADT/StringMapTest.cpp
@@ -391,21 +391,16 @@ TEST(StringMapCustomTest, InitialSizeTest) {
   for (auto Size : {1, 32, 67}) {
     StringMap<CountCtorCopyAndMove> Map(Size);
     auto NumBuckets = Map.getNumBuckets();
-
-    // Prepare the elts in a vector. We do this as a pre-step to shield us
-    // against the internals of std::pair which can introduce spurious move/copy
-    std::vector<std::pair<std::string, CountCtorCopyAndMove>> Elts;
-    for (int i = 0; i < Size; ++i)
-      Elts.emplace_back(Twine(i).str(), CountCtorCopyAndMove());
-
     CountCtorCopyAndMove::Move = 0;
     CountCtorCopyAndMove::Copy = 0;
     for (int i = 0; i < Size; ++i)
-      Map.insert(Elts[i]);
-    // After the inital copy, the map will move the Elts in the Entry.
-    EXPECT_EQ((unsigned)Size, CountCtorCopyAndMove::Move);
+      Map.insert(std::pair<std::string, CountCtorCopyAndMove>(
+          std::piecewise_construct, std::forward_as_tuple(Twine(i).str()),
+          std::forward_as_tuple(i)));
+    // After the inital move, the map will move the Elts in the Entry.
+    EXPECT_EQ((unsigned)Size * 2, CountCtorCopyAndMove::Move);
     // We copy once the pair from the Elts vector
-    EXPECT_EQ((unsigned)Size, CountCtorCopyAndMove::Copy);
+    EXPECT_EQ(0u, CountCtorCopyAndMove::Copy);
     // Check that the map didn't grow
     EXPECT_EQ(Map.getNumBuckets(), NumBuckets);
   }