llvm dev - Aug 2021 - [RFC] Deprecating the legacy pass manager for the optimization pipeline

On Tue, Aug 24, 2021 at 12:21 PM Chris Tetreault <ctetreau at quicinc.com>
wrote:
>
> Since deprecating something is giving warning that it’s going to be
removed, I don’t think it’s fair to deprecate and remove in one step. If legacy
pass manager isn’t currently formally deprecated (as in, loudly complains when
you try to use it), then I’d personally like to see it deprecated for a release
before any steps to completely remove it are taken.
I just wanted to say the same thing:)

I don't mind that we install a warning for
-DLLVM_ENABLE_NEW_PASS_MANAGER=off
in the release/13.x branch so that the signal is clearer to downstream users.
> From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of
Arthur Eubanks via llvm-dev
> Sent: Tuesday, August 24, 2021 12:10 PM
> To: Fangrui Song <maskray at google.com>
> Cc: llvm-dev <llvm-dev at lists.llvm.org>
> Subject: Re: [llvm-dev] [RFC] Deprecating the legacy pass manager for the
optimization pipeline
>
>
>
> WARNING: This email originated from outside of Qualcomm. Please be wary of
any links or attachments, and do not enable macros.
>
> I probably should have said "deprecating and removing".
>
>
>
> My intention was to remove it completely. -DLLVM_ENABLE_NEW_PASS_MANAGER
wouldn't do anything and we'd remove the
-flegacy-pass-manaager/-fexperimental-new-pass-manager flags, as well as the
corresponding lld flags.
>
>
>
> On Tue, Aug 24, 2021 at 12:02 PM Fangrui Song <maskray at google.com>
wrote:
>
> On 2021-08-24, Arthur Eubanks via llvm-dev wrote:
> >The new pass manager has been on by default since the 13 branch. Now
that
> >we've branched for 14, I'd like to start the process of
deprecating and
> >removing legacy pass manager support for the optimization pipeline.
This
> >includes clang, opt, and lld LTO support.
> >
> >Note that this doesn't apply to the codegen pipeline since
there's no new
> >pass manager support for that yet.
> >
> >Are there any objections?
>
> "deprecating" and 'removing" are different.
>
> For 14.0.0, do you plan that -DLLVM_ENABLE_NEW_PASS_MANAGER=off will
> give a warning or will be completely unsupported?


-- 
宋方睿

If nobody is setting -DLLVM_ENABLE_NEW_PASS_MANAGER=off then I'm not sure
that we need to go through the whole deprecation dance. Is there anybody
doing that?

But if we do the deprecation dance, should it be a CMake warning or a clang
warning? I'm not sure people will notice a CMake warning.
And would putting that in the 13.x branch be good enough to start removing
after 14.x?

On Tue, Aug 24, 2021 at 12:26 PM Fāng-ruì Sòng <maskray at google.com>
wrote:
> On Tue, Aug 24, 2021 at 12:21 PM Chris Tetreault <ctetreau at
quicinc.com>
> wrote:
> >
> > Since deprecating something is giving warning that it’s going to be
> removed, I don’t think it’s fair to deprecate and remove in one step. If
> legacy pass manager isn’t currently formally deprecated (as in, loudly
> complains when you try to use it), then I’d personally like to see it
> deprecated for a release before any steps to completely remove it are
taken.
>
> I just wanted to say the same thing:)
>
> I don't mind that we install a warning for
> -DLLVM_ENABLE_NEW_PASS_MANAGER=off
> in the release/13.x branch so that the signal is clearer to downstream
> users.
>
> > From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of
Arthur
> Eubanks via llvm-dev
> > Sent: Tuesday, August 24, 2021 12:10 PM
> > To: Fangrui Song <maskray at google.com>
> > Cc: llvm-dev <llvm-dev at lists.llvm.org>
> > Subject: Re: [llvm-dev] [RFC] Deprecating the legacy pass manager for
> the optimization pipeline
> >
> >
> >
> > WARNING: This email originated from outside of Qualcomm. Please be
wary
> of any links or attachments, and do not enable macros.
> >
> > I probably should have said "deprecating and removing".
> >
> >
> >
> > My intention was to remove it completely.
-DLLVM_ENABLE_NEW_PASS_MANAGER
> wouldn't do anything and we'd remove the
> -flegacy-pass-manaager/-fexperimental-new-pass-manager flags, as well as
> the corresponding lld flags.
> >
> >
> >
> > On Tue, Aug 24, 2021 at 12:02 PM Fangrui Song <maskray at
google.com>
> wrote:
> >
> > On 2021-08-24, Arthur Eubanks via llvm-dev wrote:
> > >The new pass manager has been on by default since the 13 branch.
Now
> that
> > >we've branched for 14, I'd like to start the process of
deprecating and
> > >removing legacy pass manager support for the optimization
pipeline. This
> > >includes clang, opt, and lld LTO support.
> > >
> > >Note that this doesn't apply to the codegen pipeline since
there's no
> new
> > >pass manager support for that yet.
> > >
> > >Are there any objections?
> >
> > "deprecating" and 'removing" are different.
> >
> > For 14.0.0, do you plan that -DLLVM_ENABLE_NEW_PASS_MANAGER=off will
> > give a warning or will be completely unsupported?
>
>
>
> --
> 宋方睿
>
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