[cfe-dev] One more EH patch...

[David Chisnall]

On 11 May 2009, at 20:49, Fariborz Jahanian wrote:

>
> On May 11, 2009, at 11:34 AM, Chris Lattner wrote:
>
>>
>> On May 9, 2009, at 6:09 AM, David Chisnall wrote:
>>
>>> On 9 May 2009, at 12:40, David Chisnall wrote:
>>>
>>>> This one fixes the case where an exception is thrown inside a
>>>> @catch() block (GNU runtime).
>>>
>>> And this version now emits code for @synchronized.  As with GCC,
>>> this code doesn't actually work, because the required functions are
>>> not present in the GNU runtime library.
>>
>> Thanks David, applied.  I don't have an opinion on:
>>
>>> I've also attached the test case I've been using while working on
>>> this.  The following two commands should produce the same output:
>>>
>>> clang  -lobjc -fexceptions trycatch.m -g && ./a.out
>>> gcc -lobjc -fobjc-exceptions trycatch.m && ./a.out
>>>
>>> I don't know if someone wants to add this to the clang test suite.
>>>
>>> At the moment, clang has the same behaviour as gcc when -fexceptions
>>> is not specified; it generates code which aborts at runtime if an
>>> exception is thrown, rather than handling it.  Although this is the
>>> same as gcc, it seems like the wrong thing to do.  We should
>>> probably either:
>>>
>>
>>
>>> 1) Implicitly turn on -fexceptions when @try/@catch/@throw/
>>> @synchronized is encountered, or
>>> 2) Emit an error and let the user know at compile-time that they are
>>> generating broken code.
>>>
>>>
>
> This may make sense for Gnu runtime. But for us, objc runtime library
> always
> supports the eh. Any error reporting should be done on the GNU side.

Are you sure about this?  I just compiled a trivial test function  
containing @throw, @catch and @finally with -emit-llvm -fnext-runtime  
and -fobjc2, but without -fexceptions, and it emitted bitcode  
containing references to the LLVM exception intrinsics in a function  
marked as nounwind.  This is exactly what happens on the GNU runtime  
without -fexceptions, and it results in LLVM not emitting the  
unwinding info for the function and the unwind library being unable to  
unwind into it.

David