1 files changed, 81 insertions, 0 deletions
diff --git a/test/dynamic_cast_stress.cpp b/test/dynamic_cast_stress.cpp
new file mode 100644
index 0000000..c3e5d0a
--- /dev/null
+++ b/test/dynamic_cast_stress.cpp
@@ -0,0 +1,81 @@
+//===------------------------- dynamic_cast_stress.cpp --------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cassert>
+#include <tuple>
+#include <chrono>
+#include <iostream>
+
+template <std::size_t Indx, std::size_t Depth>
+struct C
+    : public virtual C<Indx, Depth-1>,
+      public virtual C<Indx+1, Depth-1>
+{
+    virtual ~C() {}
+};
+
+template <std::size_t Indx>
+struct C<Indx, 0>
+{
+    virtual ~C() {}
+};
+
+template <std::size_t Indx, std::size_t Depth>
+struct B
+    : public virtual C<Indx, Depth-1>,
+      public virtual C<Indx+1, Depth-1>
+{
+};
+
+template <class Indx, std::size_t Depth>
+struct makeB;
+
+template <std::size_t ...Indx, std::size_t Depth>
+struct makeB<std::__tuple_indices<Indx...>, Depth>
+    : public B<Indx, Depth>...
+{
+};
+
+template <std::size_t Width, std::size_t Depth>
+struct A
+    : public makeB<typename std::__make_tuple_indices<Width>::type, Depth>
+{
+};
+
+void test()
+{
+    typedef std::chrono::high_resolution_clock Clock;
+    typedef std::chrono::duration<double, std::micro> US;
+    const std::size_t Width = 10;
+    const std::size_t Depth = 5;
+    A<Width, Depth> a;
+    typedef B<Width/2, Depth> Destination;
+//    typedef A<Width, Depth> Destination;
+    auto t0 = Clock::now();
+    Destination* b = dynamic_cast<Destination*>((C<Width/2, 0>*)&a);
+    auto t1 = Clock::now();
+    std::cout << US(t1-t0).count() << " microseconds\n";
+    assert(b != 0);
+}
+
+int main()
+{
+    test();
+}
+
+/*
+Timing results I'm seeing (median of 3 microseconds):
+
+                          libc++abi    gcc's dynamic_cast
+B<Width/2, Depth> -O3      48.334         93.190           libc++abi 93% faster
+B<Width/2, Depth> -Os      58.535         94.103           libc++abi 61% faster
+A<Width, Depth>   -O3      11.515         33.134           libc++abi 188% faster
+A<Width, Depth>   -Os      12.631         31.553           libc++abi 150% faster
+
+*/