Mingw-w64 exception handling configuration

[Jeff Law]

On 05/13/2016 08:22 PM, Sandra Loosemore wrote:
> On 05/12/2016 09:27 AM, Sandra Loosemore wrote:
>> I see that the default EH behavior for a biarch mingw-w64 target GCC is
>> to use SJLJ for the 32-bit multilib and SEH for the 64-bit one, but that
>> there are #errors in cygming.h and mingw32.h that prevent you from
>> configuring a biarch build with --disable-sjlj-exceptions to use DWARF-2
>> and SEH, respectively.  Is there a deep reason for this, or is this just
>> a case where nobody updated the configuration logic after SEH was
>> implemented?  I understand that before that, you had to use SJLJ for
>> 64-bit targets because the DWARF-2 support is restricted to 32-bit
>> targets, so it was completely reasonable to error out.
>
> Following up my own post....
>
> I did some experimentation, and it looks like this is indeed just a
> result of bit-rotten configuration logic.  I hacked up the attached
> patch against our local GCC 5.2 branch and built and tested it as a
> cross-compiler (C and C++ front ends only).  Test results for the
> --disable-sjlj-exceptions case have a few differences compared to
> --enable-sjlj-exceptions but they're not particularly better or worse.
>
> Maintainers, any guidance on getting this into trunk?  E.g. I am not
> particularly interested in Cygwin target and have not tried to build
> that, but this affects code common to both Cygwin and Mingw-w64.
Unfortunately our maintainer for the Windows targets (Kai Tietz) has 
gone silent.

The patch looks reasonable to me.  I'd go with it on the trunk, then 
backport to the release branch at a later date.

jeff