[llvm] r368339 - [MBP] Disable aggressive loop rotate in plain mode

[Xinliang David Li via llvm-commits]

How was the bisecting done -- rebuild lld each time with IR file unchanged?
The IR file generated could already be bad.

David

On Tue, Aug 13, 2019 at 12:21 AM Hans Wennborg via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Did you look at
> https://bugs.chromium.org/p/chromium/issues/detail?id=992871#c3 ? It
> shows how to reproduce using the tarball on Linux.
>
> On Mon, Aug 12, 2019 at 8:17 PM Carrot Wei <carrot at google.com> wrote:
> >
> > The MBP patch doesn't touch debug information, I suspect there is
> > something unrelated was triggered.
> > I tried your tarball, but found it is for windows, I don't have a
> > windows machine :(. Do you have a linux reproduce? It's even better to
> > have a compiler command line.
> >
> > On Mon, Aug 12, 2019 at 7:24 AM Hans Wennborg <hans at chromium.org> wrote:
> > >
> > > I've reverted this in r368579 since it causes asserts when building
> > > Chromium. See
> https://bugs.chromium.org/p/chromium/issues/detail?id=992871
> > > for details and reproducer.
> > >
> > > On Thu, Aug 8, 2019 at 10:24 PM Guozhi Wei via llvm-commits
> > > <llvm-commits at lists.llvm.org> wrote:
> > > >
> > > > Author: carrot
> > > > Date: Thu Aug  8 13:25:23 2019
> > > > New Revision: 368339
> > > >
> > > > URL: http://llvm.org/viewvc/llvm-project?rev=368339&view=rev
> > > > Log:
> > > > [MBP] Disable aggressive loop rotate in plain mode
> > > >
> > > > Patch https://reviews.llvm.org/D43256 introduced more aggressive
> loop layout optimization which depends on profile information. If profile
> information is not available, the statically estimated profile
> information(generated by BranchProbabilityInfo.cpp) is used. If user
> program doesn't behave as BranchProbabilityInfo.cpp expected, the layout
> may be worse.
> > > >
> > > > To be conservative this patch restores the original layout algorithm
> in plain mode. But user can still try the aggressive layout optimization
> with -force-precise-rotation-cost=true.
> > > >
> > > > Differential Revision: https://reviews.llvm.org/D65673
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