[libcxxabi] Disallow Base to Derived conversions for catching pointers to members.

Summary:
I accidentally implemented the 4.11 [conv.mem] conversions for libc++abi in a recent patch. @majnemer pointed out that 5.13 [except.handle] only allows the pointer conversions in 4.10 and not those is 4.11. This patch no longer allows the following example code:

```c++
struct A {};
struct B : public A {};

int main() {
  try {
    throw (int A::*)0;
  } catch (int B::*) {
    // exception caught here.
  }
}
```

Reviewers: mclow.lists, jroelofs, majnemer

Reviewed By: majnemer

Subscribers: majnemer, cfe-commits

Differential Revision: http://reviews.llvm.org/D8845

llvm-svn: 234254

1 files changed, 3 insertions, 5 deletions

diff --git a/libcxxabi/src/private_typeinfo.cpp b/libcxxabi/src/private_typeinfo.cpp
index 65cb6ed35a68..590906a45b69 100644
--- a/libcxxabi/src/private_typeinfo.cpp
+++ b/libcxxabi/src/private_typeinfo.cpp
@@ -479,11 +479,9 @@ bool __pointer_to_member_type_info::can_catch(
     if (is_equal(__context, thrown_pointer_type->__context, false))
         return true;
 
-    __dynamic_cast_info info = {__context, 0, thrown_pointer_type->__context, -1, 0};
-    info.number_of_dst_type = 1;
-    __context->has_unambiguous_public_base(&info, adjustedPtr, public_path);
-    if (info.path_dst_ptr_to_static_ptr == public_path)
-        return true;
+    // [except.handle] does not allow the pointer-to-member conversions mentioned
+    // in [mem.conv] to take place. For this reason we don't check Derived->Base
+    // for Derived->Base conversions.
 
     return false;
 }