exception handling broken on x86-64?

Hello, Robert

I had hoped this would work --- and if I use llvm-g++ to compile
exceptiontest.cpp to native code it does. But it looks like the JIT
is producing stack frames that the C++ runtime doesn't like.

Yes, surely. Emission of frames 'on fly' won't automatically make them
visible for the unwinding runtime. JIT currently doesn't register these
frames at all. I'll try to look into this issue little bit later.