> A two-phase exception-handling model is not strictly necessary to implement C++ language semantics, but it does provide some benefits. For example, the first phase allows an exception-handling mechanism to dismiss an exception before stack unwinding begins, which allows resumptive exception handling (correcting the exceptional condition and resuming execution at the point where it was raised). While C++ does not support resumptive exception handling, other languages do, and the two-phase model allows C++ to coexist with those languages on the stack.
I am aware that there have historically been other languages besides Lisp that allow resumptive exception handling (PL/I is a historical example), but I'm unaware of any modern language besides Lisp that does it.
What would C++ be coexisting with on non-mainframe hardware?
> A two-phase exception-handling model is not strictly necessary to implement C++ language semantics, but it does provide some benefits. For example, the first phase allows an exception-handling mechanism to dismiss an exception before stack unwinding begins, which allows resumptive exception handling (correcting the exceptional condition and resuming execution at the point where it was raised). While C++ does not support resumptive exception handling, other languages do, and the two-phase model allows C++ to coexist with those languages on the stack.
http://itanium-cxx-abi.github.io/cxx-abi/abi-eh.html