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author | Sirui Mu <msrlancern@gmail.com> | 2023-03-19 10:03:38 +0100 |
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committer | Nikolas Klauser <nikolasklauser@berlin.de> | 2023-03-19 10:04:34 +0100 |
commit | c9d475c937d2dc7e72ffa78acebaac3f6a2b5015 (patch) | |
tree | c1ac1dc2014c758e387578e3cc905d73b9669d75 /libcxx | |
parent | 8510cf9fc1a431b70737b2b046007d318c62b7a8 (diff) | |
download | llvm-c9d475c937d2dc7e72ffa78acebaac3f6a2b5015.zip llvm-c9d475c937d2dc7e72ffa78acebaac3f6a2b5015.tar.gz llvm-c9d475c937d2dc7e72ffa78acebaac3f6a2b5015.tar.bz2 |
[libc++abi] Improve performance of __dynamic_cast
The original `__dynamic_cast` implementation does not use the ABI-provided `src2dst_offset` parameter which helps improve performance on the hot paths. This patch improves the performance on the hot paths in `__dynamic_cast` by leveraging hints provided by the `src2dst_offset` parameter. This patch also includes a performance benchmark suite for the `__dynamic_cast` implementation.
Reviewed By: philnik, ldionne, #libc, #libc_abi, avogelsgesang
Spies: mikhail.ramalho, avogelsgesang, xingxue, libcxx-commits
Differential Revision: https://reviews.llvm.org/D138005
Diffstat (limited to 'libcxx')
-rw-r--r-- | libcxx/benchmarks/CMakeLists.txt | 1 | ||||
-rw-r--r-- | libcxx/benchmarks/libcxxabi/dynamic_cast.bench.cpp | 172 | ||||
-rw-r--r-- | libcxx/docs/ReleaseNotes.rst | 3 |
3 files changed, 176 insertions, 0 deletions
diff --git a/libcxx/benchmarks/CMakeLists.txt b/libcxx/benchmarks/CMakeLists.txt index 979e9c9..bf7c4b4 100644 --- a/libcxx/benchmarks/CMakeLists.txt +++ b/libcxx/benchmarks/CMakeLists.txt @@ -176,6 +176,7 @@ set(BENCHMARK_TESTS algorithms/sort.bench.cpp algorithms/sort_heap.bench.cpp algorithms/stable_sort.bench.cpp + libcxxabi/dynamic_cast.bench.cpp allocation.bench.cpp deque.bench.cpp deque_iterator.bench.cpp diff --git a/libcxx/benchmarks/libcxxabi/dynamic_cast.bench.cpp b/libcxx/benchmarks/libcxxabi/dynamic_cast.bench.cpp new file mode 100644 index 0000000..439eea8 --- /dev/null +++ b/libcxx/benchmarks/libcxxabi/dynamic_cast.bench.cpp @@ -0,0 +1,172 @@ +//===----------------------------------------------------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// + +#include <cstddef> + +#include "benchmark/benchmark.h" + +template <std::size_t Depth> +struct Chain : Chain<Depth - 1> {}; + +template <> +struct Chain<0> { + virtual ~Chain() noexcept = default; +}; + +template <std::size_t Index, std::size_t Depth> +struct Dag : Dag<Index, Depth - 1>, Dag<Index + 1, Depth - 1> {}; + +template <std::size_t Index> +struct Dag<Index, 0> { + virtual ~Dag() noexcept = default; +}; + +template <std::size_t Depth> +struct VChain : virtual VChain<Depth - 1> {}; + +template <> +struct VChain<0> { + virtual ~VChain() noexcept = default; +}; + +template <std::size_t Index, std::size_t Depth> +struct VDag : virtual VDag<Index, Depth - 1>, virtual VDag<Index + 1, Depth - 1> {}; + +template <std::size_t Index> +struct VDag<Index, 0> { + virtual ~VDag() noexcept = default; +}; + +template <typename Dyn, typename From, typename To = Dyn> +static void DynCast(benchmark::State& state) { + Dyn obj; + From* from_ptr = &obj; + for (auto _ : state) { + To* to_ptr = dynamic_cast<To*>(from_ptr); + benchmark::DoNotOptimize(to_ptr); + } +} + +static void StaticCast(benchmark::State& state) { + Chain<9> obj; + Chain<0>* from_ptr = &obj; + for (auto _ : state) { + Chain<9>* to_ptr = static_cast<Chain<9>*>(from_ptr); + benchmark::DoNotOptimize(to_ptr); + } +} + +// Downcast along a chain from base to the most derived type +BENCHMARK(DynCast<Chain<1>, Chain<0>>)->Name("Chain, 1 level"); +BENCHMARK(DynCast<Chain<2>, Chain<0>>)->Name("Chain, 2 levels"); +BENCHMARK(DynCast<Chain<3>, Chain<0>>)->Name("Chain, 3 levels"); +BENCHMARK(DynCast<Chain<4>, Chain<0>>)->Name("Chain, 4 levels"); +BENCHMARK(DynCast<Chain<5>, Chain<0>>)->Name("Chain, 5 levels"); +BENCHMARK(DynCast<Chain<6>, Chain<0>>)->Name("Chain, 6 levels"); +BENCHMARK(DynCast<Chain<7>, Chain<0>>)->Name("Chain, 7 levels"); +BENCHMARK(DynCast<Chain<8>, Chain<0>>)->Name("Chain, 8 levels"); +BENCHMARK(DynCast<Chain<9>, Chain<0>>)->Name("Chain, 9 levels"); + +// Downcast along a chain from base to the middle of the chain +BENCHMARK(DynCast<Chain<2>, Chain<0>, Chain<1>>)->Name("Chain middle, 1 level"); +BENCHMARK(DynCast<Chain<4>, Chain<0>, Chain<2>>)->Name("Chain middle, 2 levels"); +BENCHMARK(DynCast<Chain<6>, Chain<0>, Chain<3>>)->Name("Chain middle, 3 levels"); +BENCHMARK(DynCast<Chain<8>, Chain<0>, Chain<4>>)->Name("Chain middle, 4 levels"); + +// Downcast along a chain that fails +BENCHMARK(DynCast<Chain<1>, Chain<0>, Chain<9>>)->Name("Chain fail, 1 level"); +BENCHMARK(DynCast<Chain<2>, Chain<0>, Chain<9>>)->Name("Chain fail, 2 levels"); +BENCHMARK(DynCast<Chain<3>, Chain<0>, Chain<9>>)->Name("Chain fail, 3 levels"); +BENCHMARK(DynCast<Chain<4>, Chain<0>, Chain<9>>)->Name("Chain fail, 4 levels"); +BENCHMARK(DynCast<Chain<5>, Chain<0>, Chain<9>>)->Name("Chain fail, 5 levels"); +BENCHMARK(DynCast<Chain<6>, Chain<0>, Chain<9>>)->Name("Chain fail, 6 levels"); +BENCHMARK(DynCast<Chain<7>, Chain<0>, Chain<9>>)->Name("Chain fail, 7 levels"); +BENCHMARK(DynCast<Chain<8>, Chain<0>, Chain<9>>)->Name("Chain fail, 8 levels"); + +// Downcast along a virtual inheritance chain from base to the most derived type +BENCHMARK(DynCast<VChain<1>, VChain<0>>)->Name("VChain, 1 level"); +BENCHMARK(DynCast<VChain<2>, VChain<0>>)->Name("VChain, 2 levels"); +BENCHMARK(DynCast<VChain<3>, VChain<0>>)->Name("VChain, 3 levels"); +BENCHMARK(DynCast<VChain<4>, VChain<0>>)->Name("VChain, 4 levels"); +BENCHMARK(DynCast<VChain<5>, VChain<0>>)->Name("VChain, 5 levels"); + +// Downcast along a virtual inheritance chain from base to the middle of the chain +BENCHMARK(DynCast<VChain<2>, VChain<0>, VChain<1>>)->Name("VChain middle, 1 level"); +BENCHMARK(DynCast<VChain<4>, VChain<0>, VChain<2>>)->Name("VChain middle, 2 levels"); +BENCHMARK(DynCast<VChain<6>, VChain<0>, VChain<3>>)->Name("VChain middle, 3 levels"); +BENCHMARK(DynCast<VChain<8>, VChain<0>, VChain<4>>)->Name("VChain middle, 4 levels"); + +// Downcast along a virtual chain that fails +BENCHMARK(DynCast<VChain<1>, VChain<0>, VChain<8>>)->Name("VChain fail, 1 level"); +BENCHMARK(DynCast<VChain<2>, VChain<0>, VChain<8>>)->Name("VChain fail, 2 levels"); +BENCHMARK(DynCast<VChain<3>, VChain<0>, VChain<8>>)->Name("VChain fail, 3 levels"); +BENCHMARK(DynCast<VChain<4>, VChain<0>, VChain<8>>)->Name("VChain fail, 4 levels"); +BENCHMARK(DynCast<VChain<5>, VChain<0>, VChain<8>>)->Name("VChain fail, 5 levels"); + +// Downcast along a DAG from base to the most derived type +BENCHMARK(DynCast<Dag<0, 3>, Dag<3, 0>>)->Name("DAG rightmost, 3 levels"); +BENCHMARK(DynCast<Dag<0, 4>, Dag<4, 0>>)->Name("DAG rightmost, 4 levels"); +BENCHMARK(DynCast<Dag<0, 5>, Dag<5, 0>>)->Name("DAG rightmost, 5 levels"); +BENCHMARK(DynCast<Dag<0, 3>, Dag<0, 0>>)->Name("DAG leftmost, 3 levels"); +BENCHMARK(DynCast<Dag<0, 4>, Dag<0, 0>>)->Name("DAG leftmost, 4 levels"); +BENCHMARK(DynCast<Dag<0, 5>, Dag<0, 0>>)->Name("DAG leftmost, 5 levels"); + +// Downcast along a DAG from base to the middle of the DAG +BENCHMARK(DynCast<Dag<0, 4>, Dag<4, 0>, Dag<3, 1>>)->Name("DAG rightmost middle, 1 level"); +BENCHMARK(DynCast<Dag<0, 4>, Dag<4, 0>, Dag<2, 2>>)->Name("DAG rightmost middle, 2 levels"); +BENCHMARK(DynCast<Dag<0, 4>, Dag<4, 0>, Dag<1, 3>>)->Name("DAG rightmost middle, 3 levels"); +BENCHMARK(DynCast<Dag<0, 4>, Dag<0, 0>, Dag<0, 1>>)->Name("DAG leftmost middle, 1 level"); +BENCHMARK(DynCast<Dag<0, 4>, Dag<0, 0>, Dag<0, 2>>)->Name("DAG leftmost middle, 2 levels"); +BENCHMARK(DynCast<Dag<0, 4>, Dag<0, 0>, Dag<0, 3>>)->Name("DAG leftmost middle, 3 levels"); + +// Sidecast along a DAG +BENCHMARK(DynCast<Dag<0, 3>, Dag<3, 0>, Dag<0, 0>>)->Name("DAG sidecast, 3 levels"); +BENCHMARK(DynCast<Dag<0, 3>, Dag<2, 1>, Dag<0, 1>>)->Name("DAG sidecast, 2 levels"); +BENCHMARK(DynCast<Dag<0, 3>, Dag<1, 2>, Dag<0, 2>>)->Name("DAG sidecast, 1 level"); + +// Sidecast along a DAG that fails +BENCHMARK(DynCast<Dag<0, 3>, Dag<3, 0>, Dag<0, 4>>)->Name("DAG sidecast fail, 3 levels"); +BENCHMARK(DynCast<Dag<0, 3>, Dag<2, 1>, Dag<0, 4>>)->Name("DAG sidecast fail, 2 levels"); +BENCHMARK(DynCast<Dag<0, 3>, Dag<1, 2>, Dag<0, 4>>)->Name("DAG sidecast fail, 1 level"); + +// Downcast along a virtual inheritance DAG from base to the most derived type +BENCHMARK(DynCast<VDag<0, 3>, VDag<3, 0>>)->Name("VDAG rightmost, 3 levels"); +BENCHMARK(DynCast<VDag<0, 4>, VDag<4, 0>>)->Name("VDAG rightmost, 4 levels"); +BENCHMARK(DynCast<VDag<0, 5>, VDag<5, 0>>)->Name("VDAG rightmost, 5 levels"); +BENCHMARK(DynCast<VDag<0, 3>, VDag<0, 0>>)->Name("VDAG leftmost, 3 levels"); +BENCHMARK(DynCast<VDag<0, 4>, VDag<0, 0>>)->Name("VDAG leftmost, 4 levels"); +BENCHMARK(DynCast<VDag<0, 5>, VDag<0, 0>>)->Name("VDAG leftmost, 5 levels"); + +// Downcast along a virtual inheritance DAG from base to the middle of the DAG +BENCHMARK(DynCast<VDag<0, 3>, VDag<3, 0>, VDag<2, 1>>)->Name("VDAG rightmost middle, 1 level"); +BENCHMARK(DynCast<VDag<0, 4>, VDag<4, 0>, VDag<2, 2>>)->Name("VDAG rightmost middle, 2 levels"); +BENCHMARK(DynCast<VDag<0, 5>, VDag<5, 0>, VDag<2, 3>>)->Name("VDAG rightmost middle, 3 levels"); +BENCHMARK(DynCast<VDag<0, 3>, VDag<0, 0>, VDag<0, 1>>)->Name("VDAG leftmost middle, 1 level"); +BENCHMARK(DynCast<VDag<0, 4>, VDag<0, 0>, VDag<0, 2>>)->Name("VDAG leftmost middle, 2 levels"); +BENCHMARK(DynCast<VDag<0, 5>, VDag<0, 0>, VDag<0, 3>>)->Name("VDAG leftmost middle, 3 levels"); + +// Sidecast along a virtual inheritance DAG +BENCHMARK(DynCast<VDag<0, 3>, VDag<3, 0>, VDag<0, 0>>)->Name("VDAG sidecast, 3 levels"); +BENCHMARK(DynCast<VDag<0, 3>, VDag<2, 1>, VDag<0, 1>>)->Name("VDAG sidecast, 2 levels"); +BENCHMARK(DynCast<VDag<0, 3>, VDag<1, 2>, VDag<0, 2>>)->Name("VDAG sidecast, 1 level"); + +// Sidecast along a virtual inheritance DAG that fails +BENCHMARK(DynCast<VDag<0, 3>, VDag<3, 0>, VDag<0, 4>>)->Name("VDAG sidecast fail, 3 levels"); +BENCHMARK(DynCast<VDag<0, 3>, VDag<2, 1>, VDag<0, 4>>)->Name("VDAG sidecast fail, 2 levels"); +BENCHMARK(DynCast<VDag<0, 3>, VDag<1, 2>, VDag<0, 4>>)->Name("VDAG sidecast fail, 1 level"); + +// Cast to complete object pointer +BENCHMARK(DynCast<Chain<8>, Chain<0>, void>)->Name("Chain to complete"); +BENCHMARK(DynCast<VChain<5>, VChain<0>, void>)->Name("VChain to complete"); +BENCHMARK(DynCast<Dag<0, 3>, Dag<3, 0>, void>)->Name("DAG to complete"); +BENCHMARK(DynCast<VDag<0, 3>, VDag<3, 0>, void>)->Name("VDAG to complete"); + +// Static cast as the baseline. +BENCHMARK(StaticCast)->Name("Static"); + +BENCHMARK_MAIN(); diff --git a/libcxx/docs/ReleaseNotes.rst b/libcxx/docs/ReleaseNotes.rst index 03cab83..386ecc9 100644 --- a/libcxx/docs/ReleaseNotes.rst +++ b/libcxx/docs/ReleaseNotes.rst @@ -48,6 +48,9 @@ Improvements and New Features - ``std::string_view`` now provides iterators that check for out-of-bounds accesses when the safe libc++ mode is enabled. +- The performance of ``dynamic_cast`` on its hot paths is greatly improved and is as efficient as the + ``libsupc++`` implementation. Note that the performance improvements are shipped in ``libcxxabi``. + Deprecations and Removals ------------------------- |