Re: [GSoC]Bypass assembler when generating LTO object files

[Richard Biener <richard.guenther@gmail.com>]

On Tue, Apr 12, 2022 at 11:20 AM Jan Hubicka via Gcc <gcc@gcc.gnu.org> wrote:
>
> Hi,
> >
> >
> > > On 08-Apr-2022, at 6:32 PM, Jan Hubicka <hubicka@kam.mff.cuni.cz> wrote:
> > >
> > > Ankur,
> > >> I was browsing the list of submitted GSoC projects this year and the
> > >> project regarding bypassing assembler when generating LTO object files
> > >> caught my eye.
> > > I apologize for late reply.  I would be very happy to mentor this
> > > project.
> >
> > Thanks for the reply, but unfortunately, due to some reasons, I would not
> > be able to take part in GSoC this year.
> > But the project seems interesting and would be amazing opportunity to
> > learn a lot more things for me, so would it be okay if I try to give it a
> > go outside GSoC if no-one else picks it as their GSoC project this year ?
>
> I would be still very happy to help with that! However it would be also
> pity to not take part of GSoC, so if there is something I can help with
> on that let me know.
> >
> > >>
> > >> I already have a gcc built from source (sync-ed with trunk/master) and
> > >> launched the test-suite on it.
> > >>
> > >> I am currently in process of understanding the primilary patch
> > >> (https://gcc.gnu.org/legacy-ml/gcc/2014-09/msg00340.html), and
> > >> experimenting with it.
> > >>
> > >> are there any other things I should be aware of (useful Doc/blog or a
> > >> bug tracking the project) before proceeding further ?
> > >
> > > I think it is pretty much all that exists.  Basically we will need to
> > > implement everything that is necessary to stream out valid object file
> > > directly from GCC rather than going through gas.  The experimental
> > > prototype sort of worked but it was lacking few things.
> >
> > When I try to apply that patch on my local branch ( branched from trunk ),
> > it seem to be incompatible with the current working tree. Is there a
> > specific branch that I have to apply it to ? or is it due to the recent
> > file rename patch ( changing extensions from .c to .cc ) ?
> >
> > ```
> > $ git apply --check bypass_asm_patch
> >
> > error: patch failed: Makefile.in:1300
> > error: Makefile.in: patch does not apply
> > error: common.opt: No such file or directory
> > error: langhooks.c: No such file or directory
> > error: lto/Make-lang.in: No such file or directory
> > error: lto/lto-object.c: No such file or directory
> > error: lto/lto.c: No such file or directory
> > error: lto/lto.h: No such file or directory
> > error: lto-streamer.h: No such file or directory
> > error: toplev.c: No such file or directory
> > ```
>
> I can try to update the patch, or it probably should apply to trunk
> checked out around the date I sent the patch.  Indeed we need to change
> c to cc but there are likely more changes since then - most importnatly
> the early debug info.
> At I will see how easy/hard is to make the patch build with current
> trunk.

We do have ideas for the early debug with the asm-out abstraction to
also solve a different issue (missing simple-object support for mingw/darwin).
Namely assemble the early debug in a different file and include the resulting
native object in binary form in the compile output - not needing to write
assembly .data for that would be a good way to make this more viable.

You might want to talk to Martin Liska for this who I think had some
prototype on this?

Richard.

> Honza
> >
> > Thanks
> > - Ankur
> >