Throwing a C++ exception, under the MS ABI, is implemented using three
components:
- ThrowInfo structure which contains information like CV qualifiers,
what destructor to call and a pointer to the CatchableTypeArray.
- In a significant departure from the Itanium ABI, copying by-value
occurs in the runtime and not at the catch site. This means we need
to enumerate all possible types that this exception could be caught as
and encode the necessary information to convert from the exception
object's type to the catch handler's type. This includes complicated
derived to base conversions and the execution of copy-constructors.
N.B. This implementation doesn't support the execution of a
copy-constructor from within the runtime for now. Adding support for
that functionality is quite difficult due to things like default
argument expressions which may evaluate arbitrary code hiding in the
copy-constructor's parameters.
Differential Revision: http://reviews.llvm.org/D8066
llvm-svn: 231328
Currently, users get error messages about RTTI descriptor mangling with
no useful source location. This addresses that.
Another approach would be to disable C++ exceptions by default in the
driver when using the Microsoft C++ ABI. However, this makes it
impossible to parse system headers that use exception handling
constructs. By delaying the error to IRgen, we can figure out if we
actually need to emit code for this construct. Additionally, users who
are only interested in building refactoring tools on Windows still get a
correct AST without having to add flags. Finally, this is consistent
with what we do for SEH.
llvm-svn: 207999
David Majnemer