[LLVMdev] LLVM_REQUIRES_EH

[Dan Liew]

On 15 August 2014 02:48, Chandler Carruth <chandlerc at google.com> wrote:
>
> On Thu, Aug 14, 2014 at 6:01 PM, Reid Kleckner <rnk at google.com> wrote:
>>
>> I thought Linux distros compile LLVM with RTTI and exceptions enabled when
>> packaging.
>
>
> The question is why.
>
> RTTI makes sense -- they may well need it.
>
> But exceptions should work fine in the rest of the application even if LLVM
> is compiled with them, no?

I assume you meant to say "even if LLVM is compiled without them".

If so I was under the impression that if LLVM code built **without**
EH calls into the client code built **with** EH and that client code
then throws an exception that this exception would not be properly
propaged through the call stack. I've never tested this myself but my
reasoning came from [1] and in particular the following from [2]

```
Before detailing the library support for -fno-exceptions, first a
passing note on the things lost when this flag is used: it will break
exceptions trying to pass through code compiled with -fno-exceptions
whether or not that code has any try or catch constructs. If you might
have some code that throws, you shouldn't use -fno-exceptions. If you
have some code that uses try or catch, you shouldn't use
-fno-exceptions.
```

This is why I added the LLVM_ENABLE_EH option so if a client of LLVM
really wants to use exceptions they can.

[1] http://stackoverflow.com/questions/6524259/what-are-the-consequences-of-mixing-exception-handling-models-in-visual-studio-2
[2] https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_exceptions.html

Thanks,
Dan.