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

[Hans Wennborg via llvm-commits]

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