[libcxx-commits] [libcxx] c9d475c - [libc++abi] Improve performance of __dynamic_cast
Nikolas Klauser via libcxx-commits
libcxx-commits at lists.llvm.org
Sun Mar 19 02:05:08 PDT 2023
Author: Sirui Mu
Date: 2023-03-19T10:04:34+01:00
New Revision: c9d475c937d2dc7e72ffa78acebaac3f6a2b5015
URL: https://github.com/llvm/llvm-project/commit/c9d475c937d2dc7e72ffa78acebaac3f6a2b5015
DIFF: https://github.com/llvm/llvm-project/commit/c9d475c937d2dc7e72ffa78acebaac3f6a2b5015.diff
LOG: [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
Added:
libcxx/benchmarks/libcxxabi/dynamic_cast.bench.cpp
Modified:
libcxx/benchmarks/CMakeLists.txt
libcxx/docs/ReleaseNotes.rst
libcxxabi/src/private_typeinfo.cpp
Removed:
################################################################################
diff --git a/libcxx/benchmarks/CMakeLists.txt b/libcxx/benchmarks/CMakeLists.txt
index 979e9c9319a98..bf7c4b42b0ac6 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 0000000000000..439eea81d9a19
--- /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 03cab834485da..386ecc904a9b8 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
-------------------------
diff --git a/libcxxabi/src/private_typeinfo.cpp b/libcxxabi/src/private_typeinfo.cpp
index e1086661c019d..83d1f9f130a39 100644
--- a/libcxxabi/src/private_typeinfo.cpp
+++ b/libcxxabi/src/private_typeinfo.cpp
@@ -41,6 +41,7 @@
// Defining _LIBCXXABI_FORGIVING_DYNAMIC_CAST does not help since can_catch() calls
// is_equal() with use_strcmp=false so the string names are not compared.
+#include <cstdint>
#include <string.h>
#ifdef _LIBCXXABI_FORGIVING_DYNAMIC_CAST
@@ -656,77 +657,138 @@ __dynamic_cast(const void *static_ptr, const __class_type_info *static_type,
// Find out if we can use a giant short cut in the search
if (is_equal(dynamic_type, dst_type, false))
{
- // Using giant short cut. Add that information to info.
- info.number_of_dst_type = 1;
- // Do the search
- dynamic_type->search_above_dst(&info, dynamic_ptr, dynamic_ptr, public_path, false);
-#ifdef _LIBCXXABI_FORGIVING_DYNAMIC_CAST
- // The following if should always be false because we should definitely
- // find (static_ptr, static_type), either on a public or private path
- if (info.path_dst_ptr_to_static_ptr == unknown)
+ // We're downcasting from src_type to the complete object's dynamic
+ // type. This is a really hot path that can be further optimized
+ // with the `src2dst_offset` hint.
+ // In such a case, dynamic_ptr already gives the casting result if the
+ // casting ever succeeds. All we have to do now is to check
+ // static_ptr points to a public base sub-object of dynamic_ptr.
+
+ if (src2dst_offset >= 0)
{
- // We get here only if there is some kind of visibility problem
- // in client code.
- static_assert(std::atomic<size_t>::is_always_lock_free, "");
- static std::atomic<size_t> error_count(0);
- size_t error_count_snapshot = error_count.fetch_add(1, std::memory_order_relaxed);
- if ((error_count_snapshot & (error_count_snapshot-1)) == 0)
- syslog(LOG_ERR, "dynamic_cast error 1: Both of the following type_info's "
- "should have public visibility. At least one of them is hidden. %s"
- ", %s.\n", static_type->name(), dynamic_type->name());
- // Redo the search comparing type_info's using strcmp
- info = {dst_type, static_ptr, static_type, src2dst_offset, 0};
- info.number_of_dst_type = 1;
- dynamic_type->search_above_dst(&info, dynamic_ptr, dynamic_ptr, public_path, true);
+ // The static type is a unique public non-virtual base type of
+ // dst_type at offset `src2dst_offset` from the origin of dst.
+ // Note that there might be other non-public static_type bases. The
+ // hint only guarantees that the public base is non-virtual and
+ // unique. So we have to check whether static_ptr points to that
+ // unique public base sub-object.
+ if (offset_to_derived == -src2dst_offset)
+ dst_ptr = dynamic_ptr;
+ }
+ else if (src2dst_offset == -2)
+ {
+ // static_type is not a public base of dst_type.
+ dst_ptr = nullptr;
}
+ else
+ {
+ // If src2dst_offset == -3, then:
+ // src_type is a multiple public base type but never a virtual
+ // base type. We can't conclude that static_ptr points to those
+ // public base sub-objects because there might be other non-
+ // public static_type bases. The search is inevitable.
+
+ // Fallback to the slow path to check that static_type is a public
+ // base type of dynamic_type.
+ // Using giant short cut. Add that information to info.
+ info.number_of_dst_type = 1;
+ // Do the search
+ dynamic_type->search_above_dst(&info, dynamic_ptr, dynamic_ptr, public_path, false);
+#ifdef _LIBCXXABI_FORGIVING_DYNAMIC_CAST
+ // The following if should always be false because we should
+ // definitely find (static_ptr, static_type), either on a public
+ // or private path
+ if (info.path_dst_ptr_to_static_ptr == unknown)
+ {
+ // We get here only if there is some kind of visibility problem
+ // in client code.
+ static_assert(std::atomic<size_t>::is_always_lock_free, "");
+ static std::atomic<size_t> error_count(0);
+ size_t error_count_snapshot = error_count.fetch_add(1, std::memory_order_relaxed);
+ if ((error_count_snapshot & (error_count_snapshot-1)) == 0)
+ syslog(LOG_ERR, "dynamic_cast error 1: Both of the following type_info's "
+ "should have public visibility. At least one of them is hidden. %s"
+ ", %s.\n", static_type->name(), dynamic_type->name());
+ // Redo the search comparing type_info's using strcmp
+ info = {dst_type, static_ptr, static_type, src2dst_offset, 0};
+ info.number_of_dst_type = 1;
+ dynamic_type->search_above_dst(&info, dynamic_ptr, dynamic_ptr, public_path, true);
+ }
#endif // _LIBCXXABI_FORGIVING_DYNAMIC_CAST
- // Query the search.
- if (info.path_dst_ptr_to_static_ptr == public_path)
- dst_ptr = dynamic_ptr;
+ // Query the search.
+ if (info.path_dst_ptr_to_static_ptr == public_path)
+ dst_ptr = dynamic_ptr;
+ }
}
else
{
- // Not using giant short cut. Do the search
- dynamic_type->search_below_dst(&info, dynamic_ptr, public_path, false);
- #ifdef _LIBCXXABI_FORGIVING_DYNAMIC_CAST
- // The following if should always be false because we should definitely
- // find (static_ptr, static_type), either on a public or private path
- if (info.path_dst_ptr_to_static_ptr == unknown &&
- info.path_dynamic_ptr_to_static_ptr == unknown)
+ if (src2dst_offset >= 0)
{
- static_assert(std::atomic<size_t>::is_always_lock_free, "");
- static std::atomic<size_t> error_count(0);
- size_t error_count_snapshot = error_count.fetch_add(1, std::memory_order_relaxed);
- if ((error_count_snapshot & (error_count_snapshot-1)) == 0)
- syslog(LOG_ERR, "dynamic_cast error 2: One or more of the following type_info's "
- "has hidden visibility or is defined in more than one translation "
- "unit. They should all have public visibility. "
- "%s, %s, %s.\n", static_type->name(), dynamic_type->name(),
- dst_type->name());
- // Redo the search comparing type_info's using strcmp
- info = {dst_type, static_ptr, static_type, src2dst_offset, 0};
- dynamic_type->search_below_dst(&info, dynamic_ptr, public_path, true);
+ // Optimize toward downcasting: dst_type has one unique public
+ // static_type bases. Let's first try to do a downcast before
+ // falling back to the slow path. The downcast succeeds if there
+ // is at least one path regardless of visibility from
+ // dynamic_type to dst_type.
+ const void* dst_ptr_to_static = reinterpret_cast<const char*>(static_ptr) - src2dst_offset;
+ if (reinterpret_cast<std::intptr_t>(dst_ptr_to_static) >= reinterpret_cast<std::intptr_t>(dynamic_ptr))
+ {
+ // Try to search a path from dynamic_type to dst_type.
+ __dynamic_cast_info dynamic_to_dst_info = {dynamic_type, dst_ptr_to_static, dst_type, src2dst_offset};
+ dynamic_to_dst_info.number_of_dst_type = 1;
+ dynamic_type->search_above_dst(&dynamic_to_dst_info, dynamic_ptr, dynamic_ptr, public_path, false);
+ if (dynamic_to_dst_info.path_dst_ptr_to_static_ptr != unknown) {
+ // We have found at least one path from dynamic_ptr to
+ // dst_ptr. The downcast can succeed.
+ dst_ptr = dst_ptr_to_static;
+ }
+ }
}
-#endif // _LIBCXXABI_FORGIVING_DYNAMIC_CAST
- // Query the search.
- switch (info.number_to_static_ptr)
+
+ if (!dst_ptr)
{
- case 0:
- if (info.number_to_dst_ptr == 1 &&
- info.path_dynamic_ptr_to_static_ptr == public_path &&
- info.path_dynamic_ptr_to_dst_ptr == public_path)
- dst_ptr = info.dst_ptr_not_leading_to_static_ptr;
- break;
- case 1:
- if (info.path_dst_ptr_to_static_ptr == public_path ||
- (
- info.number_to_dst_ptr == 0 &&
- info.path_dynamic_ptr_to_static_ptr == public_path &&
- info.path_dynamic_ptr_to_dst_ptr == public_path
- )
- )
- dst_ptr = info.dst_ptr_leading_to_static_ptr;
- break;
+ // Not using giant short cut. Do the search
+ dynamic_type->search_below_dst(&info, dynamic_ptr, public_path, false);
+#ifdef _LIBCXXABI_FORGIVING_DYNAMIC_CAST
+ // The following if should always be false because we should
+ // definitely find (static_ptr, static_type), either on a public
+ // or private path
+ if (info.path_dst_ptr_to_static_ptr == unknown &&
+ info.path_dynamic_ptr_to_static_ptr == unknown)
+ {
+ static_assert(std::atomic<size_t>::is_always_lock_free, "");
+ static std::atomic<size_t> error_count(0);
+ size_t error_count_snapshot = error_count.fetch_add(1, std::memory_order_relaxed);
+ if ((error_count_snapshot & (error_count_snapshot-1)) == 0)
+ syslog(LOG_ERR, "dynamic_cast error 2: One or more of the following type_info's "
+ "has hidden visibility or is defined in more than one translation "
+ "unit. They should all have public visibility. "
+ "%s, %s, %s.\n", static_type->name(), dynamic_type->name(),
+ dst_type->name());
+ // Redo the search comparing type_info's using strcmp
+ info = {dst_type, static_ptr, static_type, src2dst_offset, 0};
+ dynamic_type->search_below_dst(&info, dynamic_ptr, public_path, true);
+ }
+#endif // _LIBCXXABI_FORGIVING_DYNAMIC_CAST
+ // Query the search.
+ switch (info.number_to_static_ptr)
+ {
+ case 0:
+ if (info.number_to_dst_ptr == 1 &&
+ info.path_dynamic_ptr_to_static_ptr == public_path &&
+ info.path_dynamic_ptr_to_dst_ptr == public_path)
+ dst_ptr = info.dst_ptr_not_leading_to_static_ptr;
+ break;
+ case 1:
+ if (info.path_dst_ptr_to_static_ptr == public_path ||
+ (
+ info.number_to_dst_ptr == 0 &&
+ info.path_dynamic_ptr_to_static_ptr == public_path &&
+ info.path_dynamic_ptr_to_dst_ptr == public_path
+ )
+ )
+ dst_ptr = info.dst_ptr_leading_to_static_ptr;
+ break;
+ }
}
}
return const_cast<void*>(dst_ptr);
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