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

[Hubert Tong via cfe-dev]

On Tue, Apr 4, 2017 at 8:19 AM, Aaron Ballman <aaron at aaronballman.com>
wrote:

> On Wed, Mar 22, 2017 at 8:45 PM, Hubert Tong via cfe-dev
> <cfe-dev at lists.llvm.org> wrote:
> > On Wed, Mar 22, 2017 at 7:21 PM, Hal Finkel <hfinkel at anl.gov> wrote:
> >>
> >>
> >> On 03/22/2017 06:17 PM, Hubert Tong via cfe-dev wrote:
> >>
> >> -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.
> >>
> >>
> >> To summarize, code compiled with -fignore-exceptions can throw, but
> can't
> >> catch anything. All exceptions just unwind through all such code. Is
> that
> >> right?
> >
> > That depends on what you mean by "unwind". Exceptions will go past all
> such
> > code without executing destructors.
>
> Will throwing always result in calling std::terminate()? If so, does
> that call happen immediately upon executing the throw statement?
>
> Or, if you have one TU compiled with -fignore-exceptions that throws,
> and a second TU with -fno-ignore-exceptions that catches the exception
> thrown from the first TU, can the exception still be caught?
>
The exception can still be caught.


>
> ~Aaron
>
> >
> >>
> >>
> >>  -Hal
> >>
> >>
> >> -- HT
> >>
> >>
> >>
> >> _______________________________________________
> >> cfe-dev mailing list
> >> cfe-dev at lists.llvm.org
> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
> >>
> >>
> >> --
> >> Hal Finkel
> >> Lead, Compiler Technology and Programming Languages
> >> Leadership Computing Facility
> >> Argonne National Laboratory
> >
> >
> >
> > _______________________________________________
> > cfe-dev mailing list
> > cfe-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
> >
>
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