[llvm-dev] LLD status update and performance chart

[Rui Ueyama via llvm-dev]

On Tue, Dec 13, 2016 at 10:37 AM, Hal Finkel via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> ----- Original Message -----
> > From: "Rafael Avila de Espindola via llvm-dev" <llvm-dev at lists.llvm.org>
> > To: "Mehdi Amini" <mehdi.amini at apple.com>
> > Cc: "llvm-dev" <llvm-dev at lists.llvm.org>
> > Sent: Tuesday, December 13, 2016 12:10:08 PM
> > Subject: Re: [llvm-dev] LLD status update and performance chart
> >
> > Mehdi Amini <mehdi.amini at apple.com> writes:
> >
> > >> On Dec 13, 2016, at 9:40 AM, Rafael Avila de Espindola
> > >> <rafael.espindola at gmail.com> wrote:
> > >>
> > >> Mehdi Amini <mehdi.amini at apple.com> writes:
> > >>
> > >>>> On Dec 13, 2016, at 5:55 AM, Rafael Avila de Espindola via
> > >>>> llvm-dev <llvm-dev at lists.llvm.org> wrote:
> > >>>>
> > >>>> Sean Silva via llvm-dev <llvm-dev at lists.llvm.org> writes:
> > >>>>> This will also greatly facilitate certain measurements I'd like
> > >>>>> to do
> > >>>>> w.r.t. different strategies for avoiding memory costs for input
> > >>>>> files (esp.
> > >>>>> minor faults and dTLB costs). I've almost gotten to the point
> > >>>>> of
> > >>>>> implementing this just to do those measurements.
> > >>>>
> > >>>> If you do please keep it local. The bare minimum we have of
> > >>>> library
> > >>>> support is already disproportionately painful and prevents
> > >>>> easier sharing
> > >>>> with COFF. We should really not add more until the linker is
> > >>>> done.
> > >>>
> > >>> This is so much in contrast with the LLVM development, I find it
> > >>> quite hard to see this as an acceptable position on llvm-dev.
> > >>
> > >> Why? What is wrong with setting priorities and observing that what
> > >> library support we already have has had a disproportional cost?
> > >
> > > The library-hostile lld development goes against one the core
> > > principles that, I believe, drives the LLVM development: providing
> > > libraries and reusable components.
> >
> > Because it is trying to do something fundamentally different. We are
> > trying to write a *program*.
>
> But this is not a technical argument. As a project, we rarely write
> programs, as such. We generally create reusable components that happen to
> have driver executables. At least long term, I think there's consensus that
> this is the best path. If we're going to make a different choice in this
> case, we need concrete reasons. We should discuss this in the context of
> the reasons you've provided (error handling, etc.).
>

Please tell me what you think about how reusable components would be like.
Which parts of the linker can be reusable components? Is that really
feasible? You are saying that the linker should be written in different way
by comparing it with an ideal linker (modular, reusable and fast! and by
the way the current LLD is much more reusable and extensible than before in
my opinion), but you can say anything if you compare with an ideal one. You
need to prove that it's doable so we should do that way instead of this. We
(or I) did a large experiment with the old LLD for years but couldn't find
a way to make it possible in a reasonable manner. I'm still trying to find
one, by distilling ELF and COFF linkers common parts, but still couldn't
make it.
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