Re: PATCH: sjlj exceptions

["John David Anglin" <dave at hiauly1 dot hia dot nrc dot ca>]

>   In message <200010272021.QAA08569@hiauly1.hia.nrc.ca>you write:
>   > This patch resolves to some extent the problems noted in these two postings
>   > :
>   > <http://gcc.gnu.org/ml/gcc-bugs/2000-08/msg00687.html> and
>   > <http://gcc.gnu.org/ml/gcc-bugs/2000-10/msg00083.html>.  My investigation
>   > revealed that the problem is only present when sjlj exceptions are used.
>   > The memory expansion occured in the gcse pass and was a result of the
>   > large number of edges present in functions using sjlj exceptions.
> I believe if you look at Richard's recent changes to the SJLJ exception
> handling code you'll find that we now build a better CFG (specifically we
> don't have nearly as many useless edges).
> 
> For a testcase I'm dealing with right now it's drastically reduced both the
> memory requirements and compile times.  To give you some idea, the test
> takes > 40 minutes to compile without the patch and > 200M of memory
> (I didn't bother waiting for it to complete, so I have no idea how long
> it would take to finish or whether or not the peak memory usage would
> increase).  After Richard's patch we're on the order of 7 minutes and
> 100M of memory.
> 
> There is one bug introduced by Richard's patch that I'll post a fix for
> shortly.

This is great news.  However, it appears that gcse_main still punts when
current_function_calls_setjmp. The function expand_builtin_setjmp_setup
sets this, so I think the memory reduction might be due to the gcse pass
being disabled.

I had seen failures in the bb reorder pass both with and without
DONT_USE_BUILTIN_SETJMP defined.  The failures when it is defined are
more common.  However, I found a failure when it was not defined
building groff.  In both cases, the reordering caused NOTE_INSN_EH_REGION_END
notes to be placed before the corresponding NOTE_INSN_EH_REGION_BEG note.
It will be interesting to see if the new changes fix the problem.
resolve the problem that

Dave
-- 
J. David Anglin                                  dave.anglin@nrc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6605)