forked from OSchip/llvm-project
[ADT] Add resize_for_overwrite method to SmallVector.
Analagous to the std::make_(unqiue|shared)_for_overwrite added in c++20. If T is POD, and the container gets larger, any new values added wont be initialized. This is useful when using SmallVector as a buffer where its planned to overwrite any potential new values added. If T is not POD, `new (Storage) T` functions identically to `new (Storage) T()` so this will function identically to `resize(size_type)`. Reviewed By: dexonsmith Differential Revision: https://reviews.llvm.org/D93532
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@ -460,7 +460,8 @@ public:
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this->Size = 0;
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}
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void resize(size_type N) {
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private:
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template <bool ForOverwrite> void resizeImpl(size_type N) {
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if (N < this->size()) {
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this->destroy_range(this->begin()+N, this->end());
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this->set_size(N);
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@ -468,11 +469,20 @@ public:
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if (this->capacity() < N)
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this->grow(N);
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for (auto I = this->end(), E = this->begin() + N; I != E; ++I)
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if (ForOverwrite)
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new (&*I) T;
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else
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new (&*I) T();
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this->set_size(N);
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}
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}
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public:
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void resize(size_type N) { resizeImpl<false>(N); }
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/// Like resize, but \ref T is POD, the new values won't be initialized.
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void resize_for_overwrite(size_type N) { resizeImpl<true>(N); }
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void resize(size_type N, const T &NV) {
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if (N == this->size())
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return;
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@ -341,6 +341,31 @@ TYPED_TEST(SmallVectorTest, ResizeFillTest) {
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this->assertValuesInOrder(this->theVector, 3u, 77, 77, 77);
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}
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TEST(SmallVectorTest, ResizeForOverwrite) {
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{
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// Heap allocated storage.
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SmallVector<unsigned, 0> V;
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V.push_back(5);
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V.pop_back();
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V.resize_for_overwrite(V.size() + 1);
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EXPECT_EQ(5, V.back());
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V.pop_back();
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V.resize(V.size() + 1);
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EXPECT_EQ(0, V.back());
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}
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{
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// Inline storage.
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SmallVector<unsigned, 2> V;
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V.push_back(5);
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V.pop_back();
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V.resize_for_overwrite(V.size() + 1);
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EXPECT_EQ(5, V.back());
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V.pop_back();
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V.resize(V.size() + 1);
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EXPECT_EQ(0, V.back());
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}
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}
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// Overflow past fixed size.
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TYPED_TEST(SmallVectorTest, OverflowTest) {
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SCOPED_TRACE("OverflowTest");
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