[llvm-dev] New Pass Manager with flto[=thin] not enabled (??)

[Teresa Johnson via llvm-dev]

Hi Graham,

This looks like an oversight. Agree that the way of passing options through
to the linkers is not great as it requires adding plumbing through the
driver. But I think that is the best option for now. It would entail adding
a gold-plugin option that would be set from the clang driver and using that
to set Conf.UseNewPM. Do you want to send this patch?

Thanks,
Teresa

On Tue, Oct 3, 2017 at 12:38 PM, Graham Yiu via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi David,
>
> Hi David,
>
> So I should note that we're only interested in the gold linker with
> LTO/thinLTO. It didn't occur to me at the time that we also need to account
> for lld.
>
> I noticed the current way of passing options to gold plugin is slightly
> hacky, in that there are handful of options we define and pass to gold
> specifically like -O<#> or -mcpu=[arch]. This seems like it'll be a
> maintenance nightmare in the future.
>
> Also, are there ways to embed options into bitcode files from the compile
> step?
>
> Graham Yiu
> LLVM Compiler Development
> IBM Toronto Software Lab
> Office: (905) 413-4077 C2-707/8200/Markham
> Email: gyiu at ca.ibm.com
>
> [image: Inactive hide details for Davide Italiano ---10/03/2017 03:14:18
> PM---On Tue, Oct 3, 2017 at 12:08 PM, Davide Italiano <davide@]Davide
> Italiano ---10/03/2017 03:14:18 PM---On Tue, Oct 3, 2017 at 12:08 PM,
> Davide Italiano <davide at freebsd.org> wrote: > On Tue, Oct 3, 2017 a
>
> From: Davide Italiano <davide at freebsd.org>
> To: Graham Yiu <gyiu at ca.ibm.com>
> Cc: llvm-dev <llvm-dev at lists.llvm.org>
> Date: 10/03/2017 03:14 PM
> Subject: Re: [llvm-dev] New Pass Manager with flto[=thin] not enabled (??)
> Sent by: davide.italiano at gmail.com
> ------------------------------
>
>
>
> On Tue, Oct 3, 2017 at 12:08 PM, Davide Italiano <davide at freebsd.org>
> wrote:
> > On Tue, Oct 3, 2017 at 11:57 AM, Graham Yiu via llvm-dev
> > <llvm-dev at lists.llvm.org> wrote:
> >> Hello,
> >>
> >> I recently noticed that the new pass manager was not enabled at
> regular/thin
> >> LTO link step even if '-fexperimental-new-pass-manager' was specified
> in the
> >> compile step and link step commands. Upon closer inspection, it seems
> >> there's so real way to invoke the new pass manager path
> ('runNewPMPasses' in
> >> lib/LTO/LTOBackend.cpp) during link step.
> >>
> >
> > `-fexperimental-new-pass-manager` is a compile time flag and has no
> > effect on the link step IIRC.
> > You may want to teach the driver to pass the correct flag to the LTO
> > plugin in gold or to lld.
> >
> > --
> > Davide
>
> For lld in particular, currently there's only the ability to specifiy
> a custom pass pipeline when passing `--lto-newpm-passes` to the
> linker. This is because, historically, when I added this flag, the
> pass manager work was still in progress and the `-O2/LTO` pipeline
> wasn't fleshed entirely (missing passes & functionality).
> You can probably add the option to lld now, if you can't/don't know
> how to do it, I may take a look this weekend.
>
> Thanks,
>
> --
> Davide
>
> "There are no solved problems; there are only problems that are more
> or less solved" -- Henri Poincare
>
>
>
>
>
> _______________________________________________
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>


-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |  408-460-2413
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