[gambit-list] The monster that killed gcc

Dimitris Vyzovitis vyzo at hackzen.org
Mon Mar 19 15:05:06 EDT 2018


Sure, I'd like to get to the bottom of this because it's such an ugly
failure mode!

For now, I changed the gerbil compiler to emit an inlining-limit
declaration in meta phases (that's where the syntax-case monsters reside).

-- vyzo

On Mon, Mar 19, 2018 at 9:02 PM, Marc Feeley <feeley at iro.umontreal.ca>
wrote:

> I think you should figure out which of the configure options
>
>   --enable-single-host
>   --enable-c-opt
>   --enable-gcc-opts
>
> are the most useful/beneficial for the kind of code generated by Gerbil.
> I suspect that --enable-single-host is the most performance-enhancing
> option, and --enable-c-opt only gives a marginal speed increase at the cost
> of a much higher C compile time.
>
> If you do try the various combinations, please report your results here.
> I’d like to know if my intuition is correct.
>
> Marc
>
>
>
> > On Mar 19, 2018, at 2:56 PM, Dimitris Vyzovitis <vyzo at hackzen.org>
> wrote:
> >
> > My gambit is configured with  --enable-single-host --enable-c-opt
> --enable-gcc-opts.
> > I have 8G on my current laptop, but I run without a swap; the death
> occurs at around 6G.
> > It's not only the memory usage though, it takes forever too. clang on
> travis didn't OOM, but it took 15min on the file.
> >
> > I think it might be a case of really bad interaction between the various
> optimizers in the 3 compilers involved. The gerbil emitted code is already
> heavily optimized to perform match tree linearization (I have a shiny new
> optimizer that optimizes match and syntax- case expansions).
> > That means you can't reasonably inline anything other than single use
> procedures within the optimized blocks.
> >
> > -- vyzo
> >
> >
> > On Mon, Mar 19, 2018 at 8:41 PM, Marc Feeley <feeley at iro.umontreal.ca>
> wrote:
> > The default inlining-limit is 350, so the expansion from 100 is quite
> possible.
> >
> > But the problem here is that gcc chokes on the compilation of the C
> file.  So… what are the compilation options passed to gcc?
> >
> > - are you using --enable-single-host ?
> > - are you using a higher level of optimization such as -O2 or -O3 rather
> than the default -O1 ?
> >
> > These will definitely increase the pressure on the C compiler.  Also,
> some versions of gcc do a better job at compiling large C files.  The file
> lib/_io.c in the Gambit distribution is about 90kloc and I have never
> gotten an OOM error from gcc while compiling it, even though I use a “make
> -j 8” (8 C compilations in parallel).  I do have 16 GB of RAM on my
> machine… how much RAM do you have on yours?
> >
> > Marc
> >
> >
> >
> > > On Mar 19, 2018, at 2:31 PM, Dimitris Vyzovitis <vyzo at hackzen.org>
> wrote:
> > >
> > > It's 140kloc without the inlining declaration and just 22Kloc with the
> declaration.
> > >
> > > -- vyzo
> > >
> > > On Mon, Mar 19, 2018 at 8:27 PM, Marc Feeley <feeley at iro.umontreal.ca>
> wrote:
> > > Out of curiosity, what is the number of LOC of C with and without the
> inlining-limit?
> > >
> > > I’m just wondering if this should be classified as an issue, or if the
> inliner is just doing its work as expected.
> > >
> > > Marc
> > >
> > >
> > >
> > > > On Mar 19, 2018, at 2:23 PM, Dimitris Vyzovitis <vyzo at hackzen.org>
> wrote:
> > > >
> > > > It seems it's the inliner going haywire -- if I add a (declare
> (inlining-limit 100)), then it compiles in 20s.
> > > >
> > > > -- vyzo
> > > >
> > > > On Mon, Mar 19, 2018 at 7:29 PM, Dimitris Vyzovitis <
> vyzo at hackzen.org> wrote:
> > > > The attached file results in a 140kloc monster that results in gcc
> dying with OOM after several minutes of effort, and I would like to
> understand why.
> > > > Any ideas?
> > > >
> > > > -- vyzo
> > > >
> > >
> > >
> >
> >
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.iro.umontreal.ca/pipermail/gambit-list/attachments/20180319/e72ec57d/attachment.htm>


More information about the Gambit-list mailing list