SmallVector: support resize(N) with move-only types

Unfortunately there's no way to elegantly do this with pre-canned
algorithms. Using a generating iterator doesn't work because you default
construct for each element, then move construct into the actual slot
(bad for copy but non-movable types, and a little unneeded overhead even
in the move-only case), so just write it out manually.

This solution isn't exception safe (if one of the element's ctors calls
we don't fall back, destroy the constructed elements, and throw on -
which std::uninitialized_fill does do) but SmallVector (and LLVM) isn't
exception safe anyway.

llvm-svn: 210495

include/llvm/ADT/SmallVector.h

@@ -380,7 +380,8 @@ public:
     } else if (N > this->size()) {
       if (this->capacity() < N)
         this->grow(N);
-      std::uninitialized_fill(this->end(), this->begin()+N, T());
+      for (auto I = this->end(), E = this->begin() + N; I != E; ++I)
+        new (&*I) T();
       this->setEnd(this->begin()+N);
     }
   }

unittests/ADT/SmallVectorTest.cpp

@@ -139,6 +139,19 @@ int Constructable::numAssignmentCalls;
 int Constructable::numCopyAssignmentCalls;
 int Constructable::numMoveAssignmentCalls;
 
+struct NonCopyable {
+  NonCopyable() {}
+  NonCopyable(NonCopyable &&) {}
+  NonCopyable &operator=(NonCopyable &&) { return *this; }
+  NonCopyable(const NonCopyable &) = delete;
+  NonCopyable &operator=(const NonCopyable &) = delete;
+};
+
+LLVM_ATTRIBUTE_USED void CompileTest() {
+  SmallVector<NonCopyable, 0> V;
+  V.resize(42);
+}
+
 // Test fixture class
 template <typename VectorT>
 class SmallVectorTest : public testing::Test {
@@ -277,13 +290,26 @@ TYPED_TEST(SmallVectorTest, ResizeGrowTest) {
 
   this->theVector.resize(2);
 
-  // The extra constructor/destructor calls come from the temporary object used
-  // to initialize the contents of the resized array (via copy construction).
-  EXPECT_EQ(3, Constructable::getNumConstructorCalls());
-  EXPECT_EQ(1, Constructable::getNumDestructorCalls());
+  EXPECT_EQ(2, Constructable::getNumConstructorCalls());
+  EXPECT_EQ(0, Constructable::getNumDestructorCalls());
   EXPECT_EQ(2u, this->theVector.size());
 }
 
+TYPED_TEST(SmallVectorTest, ResizeWithElementsTest) {
+  this->theVector.resize(2);
+
+  Constructable::reset();
+
+  this->theVector.resize(4);
+
+  size_t Ctors = Constructable::getNumConstructorCalls();
+  EXPECT_TRUE(Ctors == 2 || Ctors == 4);
+  size_t MoveCtors = Constructable::getNumMoveConstructorCalls();
+  EXPECT_TRUE(MoveCtors == 0 || MoveCtors == 2);
+  size_t Dtors = Constructable::getNumDestructorCalls();
+  EXPECT_TRUE(Dtors == 0 || Dtors == 2);
+}
+
 // Resize with fill value.
 TYPED_TEST(SmallVectorTest, ResizeFillTest) {
   SCOPED_TRACE("ResizeFillTest");