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MS ABI: Implement support for throwing a C++ exception

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MS ABI: Implement support for throwing a C++ exception

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

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