[cfe-dev] RFC: allowing EH constructs, but not generating handlers/cleanups

[Hubert Tong via cfe-dev]

-fno-exceptions causes EH constructs such as try/catch,
function-try-blocks, and throw expressions to be diagnosed with a severe
error. That is, -f[no-]exceptions controls a language-support property.

For experiments in evaluating the cost of (unused) exception handling, and
for cases where components are being deployed with the expectation that
exceptions will not be thrown, etc. it is useful to allow EH constructs in
the source, but to generate code with no handlers or cleanups.

I think that it still makes sense under such a mode to allow throw
expressions to throw. This is consistent with -fno-exceptions still calling
__cxa_bad_cast and __cxa_bad_typeid (which GCC also does, but not with
__cxa_throw_bad_array_new_length).

That is, the proposed semantics is essentially the same as for
-fno-exceptions, except to treat try/catch and function-try-blocks as just
normal code introducing no handlers, and to allow throw expressions.

-fno-exceptions already suppresses creation of cleanups for unwinding and
the ignoring of exception specifications.

I like to think of this as -fignore-exceptions. I have a use for this, and
I would like to know what people think.

-- HT
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