Author: Nathan James Date: 2020-12-22T17:18:59Z New Revision: 5d10b8ad595da87bec8c66ad70a8daf86cd9266b
URL: https://github.com/llvm/llvm-project/commit/5d10b8ad595da87bec8c66ad70a8daf86cd9266b DIFF: https://github.com/llvm/llvm-project/commit/5d10b8ad595da87bec8c66ad70a8daf86cd9266b.diff LOG: [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 Added: Modified: llvm/include/llvm/ADT/SmallVector.h llvm/unittests/ADT/SmallVectorTest.cpp Removed: ################################################################################ diff --git a/llvm/include/llvm/ADT/SmallVector.h b/llvm/include/llvm/ADT/SmallVector.h index 0a0f09c68060..3bbde2d9c0fb 100644 --- a/llvm/include/llvm/ADT/SmallVector.h +++ b/llvm/include/llvm/ADT/SmallVector.h @@ -460,7 +460,8 @@ class SmallVectorImpl : public SmallVectorTemplateBase<T> { this->Size = 0; } - void resize(size_type N) { +private: + template <bool ForOverwrite> void resizeImpl(size_type N) { if (N < this->size()) { this->destroy_range(this->begin()+N, this->end()); this->set_size(N); @@ -468,11 +469,20 @@ class SmallVectorImpl : public SmallVectorTemplateBase<T> { if (this->capacity() < N) this->grow(N); for (auto I = this->end(), E = this->begin() + N; I != E; ++I) - new (&*I) T(); + if (ForOverwrite) + new (&*I) T; + else + new (&*I) T(); this->set_size(N); } } +public: + void resize(size_type N) { resizeImpl<false>(N); } + + /// Like resize, but \ref T is POD, the new values won't be initialized. + void resize_for_overwrite(size_type N) { resizeImpl<true>(N); } + void resize(size_type N, const T &NV) { if (N == this->size()) return; diff --git a/llvm/unittests/ADT/SmallVectorTest.cpp b/llvm/unittests/ADT/SmallVectorTest.cpp index 957412f3083f..e02c3e709667 100644 --- a/llvm/unittests/ADT/SmallVectorTest.cpp +++ b/llvm/unittests/ADT/SmallVectorTest.cpp @@ -341,6 +341,31 @@ TYPED_TEST(SmallVectorTest, ResizeFillTest) { this->assertValuesInOrder(this->theVector, 3u, 77, 77, 77); } +TEST(SmallVectorTest, ResizeForOverwrite) { + { + // Heap allocated storage. + SmallVector<unsigned, 0> V; + V.push_back(5); + V.pop_back(); + V.resize_for_overwrite(V.size() + 1); + EXPECT_EQ(5, V.back()); + V.pop_back(); + V.resize(V.size() + 1); + EXPECT_EQ(0, V.back()); + } + { + // Inline storage. + SmallVector<unsigned, 2> V; + V.push_back(5); + V.pop_back(); + V.resize_for_overwrite(V.size() + 1); + EXPECT_EQ(5, V.back()); + V.pop_back(); + V.resize(V.size() + 1); + EXPECT_EQ(0, V.back()); + } +} + // Overflow past fixed size. TYPED_TEST(SmallVectorTest, OverflowTest) { SCOPED_TRACE("OverflowTest"); _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
