[LLVMdev] Test Suite - Livermore Loops

[Daniel Dunbar]

On Mon, Jan 7, 2013 at 1:52 PM, David Blaikie <dblaikie at gmail.com> wrote:

> On Mon, Jan 7, 2013 at 1:46 PM, Daniel Dunbar <daniel at zuster.org> wrote:
> >
> >
> >
> > On Mon, Jan 7, 2013 at 1:14 PM, David Blaikie <dblaikie at gmail.com>
> wrote:
> >>
> >> On Mon, Jan 7, 2013 at 12:58 PM, Daniel Dunbar <daniel at zuster.org>
> wrote:
> >> > To weigh in here...
> >> >
> >> >
> >> > On Thu, Jan 3, 2013 at 8:15 AM, David Blaikie <dblaikie at gmail.com>
> >> > wrote:
> >> >>
> >> >> +Daniel & Michael who work on the LNT infrastructure & might have
> some
> >> >> thoughts on the differences & their merits & motivations.
> >> >>
> >> >> On Thu, Jan 3, 2013 at 4:05 AM, Renato Golin <
> renato.golin at linaro.org>
> >> >> wrote:
> >> >> > David,
> >> >> >
> >> >> > I got some more work on the Livermore Loops and I found out that
> the
> >> >> > issue
> >> >> > is the difference in the parameters between a single step and a
> multi
> >> >> > step
> >> >> > compilation.
> >> >>
> >> >> Thanks for the investigation.
> >> >>
> >> >> > When you compile "clang kernel06.c" it works fine, but when you get
> >> >> > all
> >> >> > steps (clang -emit-llvm + llvm-as + opt + llc etc), the defaults
> >> >> > options
> >> >> > of
> >> >> > each and how they interact is showing a bug in the code generated.
> >> >>
> >> >> Sounds quite plausible.
> >> >>
> >> >> > This difference is due to the fact that I'm running the test-suite
> >> >> > using
> >> >> > LNT, while the build bots are running it using Make directly. I'd
> >> >> > expect
> >> >> > them both to be the same, but apparently they're quite different in
> >> >> > what
> >> >> > kind of parameters they use, passes they test and results they get.
> >> >> >
> >> >> > I think there are two courses of action here:
> >> >> >
> >> >> > 1. Identify the issue, isolate the case and create a bug to resolve
> >> >> > later.
> >> >> > 2. Make sure LNT does exactly what the build bots are doing
> >> >>
> >> >> Part of the issue here is whether or not the Make-based execution is
> >> >> still maintained/valued. I'm getting the impression that the LNT
> >> >> execution may be already, or be becoming, the standard way to run the
> >> >> test suite even when not gathering perf statistics. Michael/Daniel -
> >> >> is that the case?
> >> >
> >> >
> >> > Well, the distinction isn't really between LNT and non-LNT, its
> between
> >> > the
> >> > TEST=nightly and TEST=simple style supported by the Makefiles. LNT
> uses
> >> > the
> >> > TEST=simple style and that is all I care to support.
> >>
> >> Fair enough, though that's sort of what I was getting at in a way:
> >> whatever way LNT is driving the test-suite is, essentially, the only
> >> supported way. Sure we can have non-LNT bots (not ideal, perhaps -
> >> still another path to maintain/possibly diverge by accident) but they
> >> certainly shouldn't be using anything other than the way LNT uses the
> >> test-suite (ie: TEST=simple).
> >>
> >> Can we kill TEST=nightly, then, since it's just an
> >> untested/unsupported trap? Or do you know of users that have a need
> >> for this?
> >
> >
> > It's untested, but as supported as anything else (I try not to break it,
> and
> > will fix bugs in it).
> >
> > And yes, there are still users that use this regularly. Most of that is
> > probably habit among old-school LLVMers, but it's still useful when you
> want
> > to do direct A/B testing of optimizer changes (support for things like
> > OPTBETA and LLCBETA), or when you want to test a change without
> requiring a
> > compiler rebuild.
> >
> > For example, we still don't have very good support in the compiler for
> > tweaking various parts of the compilation process (for example, running
> with
> > a custom pass list), so the easiest way to test addition of a new pass
> may
> > still be using TEST=nightly.
> >
> > My natural tendency is towards "if it isn't broke, don't kill it", and
> not
> > to try and remove it until we have a new separate way of running the test
> > suite outside of the Makefiles.
> >
> >>
> >> >
> >> > Historically, the old way of testing (TEST=nightly) used the various
> >> > LLVM
> >> > tools to effect a compilation because there weren't compilers that
> >> > worked.
> >> > However, this is a bad way to "test" the product that most users
> >> > actually
> >> > care about, which is the compiler.
> >> >
> >> > With TEST=simple, all the compilation is done using the compiler just
> as
> >> > an
> >> > end user would. If you want LTO, the right way to get it is to use the
> >> > compilers support for LTO. This is how we test LTO internally. I've
> >> > never
> >> > tried to get LTO working on Linux, but it should be possible using the
> >> > gold
> >> > plugin and passing the right compiler options.
> >> >
> >> >> If so, should we rip out the direct Make execution, or do something
> to
> >> >> otherwise warn/disable it?
> >> >
> >> >
> >> > Per my other thread polling users of the test-suite, there are still
> >> > people
> >> > who use the Makefiles to do more custom things. I personally would
> love
> >> > to
> >> > deprecate them completely, but they do support some useful workflows.
> >> >
> >> > My ideal would be:
> >> > 1. Migrate LNT to drive the test-suite using a more sane mechanism
> (not
> >> > a
> >> > glob of Makefiles). I would like the "more sane mechanism" to be
> >> > lit-based.
> >> > 2. Maybe do some work to make using lit to drive the test-suite more
> >> > convenient and hopefully support some of the useful workflows the
> >> > Makefiles
> >> > support with less of the crap.
> >> > 3. Deprecate the Makefiles, or at least let the die through lack of
> >> > maintenance.
> >> >
> >> > Does that answer the parts you wanted my input on?
> >>
> >> More or less, I suppose I wouldn't mind an opinion on the "should we
> >> kill off/migrate bots from test-suite invocation to LNT?" issue too.
> >> (my assumption is that your answer to that is "yes", but just want to
> >> be clear)
> >
> >
> > Yes, definitely.
>
> Hmm, this seems at odds with your above opinion on not killing
> TEST=nightly, though. If we actively migrate bots away from
> TEST=nightly we're going to break it (indeed we Renato already has
> which is how this thread came up).


By "not breaking it", I meant the infrastructure of it, not whether or not
the tests work or not.

As for the actual LLVM bug, we should probably try and get an LTO LNT bot
up, though, which would most likely hit the same bug.

If it's broken that, I would think,
> is going to cause some confusion/problems for those using it &
> expecting things to pass. Is your impression/experience that those
> running this manually for custom testing aren't too concerned about
> spurious failures?
>

In my mind, I don't necessarily think "its broken" makes sense in this
context. It's not TEST=nightly that is broken, it is the compiler in the
context of a one architecture, one set of compile options, etc.

I expect/hope developers to be aware that compiler bugs may only manifest
under a very specific set of circumstances, and so they need to run their
tests in the same way as the buildbots if they want results to match. And I
hope most core LLVM developers realize that the way TEST=nightly ends up
building binaries is very different from using the compiler directly, but
if not most of them figure this out very quickly in practice.

I see LNT + TEST=simple as the "right way" to do large scale testing w/ the
test suite and buildbots, but if developers want to use TEST=nightly for
experiments or development its still there. I have actively tried to
encourage people to switch over to using TEST=simple when possible, but its
hard to get people to change existing workflows if there isn't a clear
benefit.

 - Daniel


>
> - David
>
> >
> >  - Daniel
> >
> >>
> >>
> >> - David
> >>
> >> >
> >> >  - Daniel
> >> >
> >> >>
> >> >> > I'm working on item 1 right now, not sure how item 2 can be
> solved...
> >> >> >
> >> >> > Of course, the fact that it's the not same flow meant we caught a
> bug
> >> >> > in
> >> >> > LLVM, but that's bound to create more confusion and broken commits,
> >> >> > which is
> >> >> > worse in the long run.
> >> >>
> >> >> Yeah, unless there's some strong/specific motivation for this I'd be
> >> >> in favor of removing the difference (or removing the Make-based
> >> >> execution entirely)
> >> >>
> >> >> > Also, if we're not running LNT as often as buildbots, the benefit
> of
> >> >> > having
> >> >> > them different is sporadic at best.
> >> >>
> >> >> we're running both pretty regularly, I think - if anything I suspect
> >> >> we might be running LNT on more configurations than the Make-based
> >> >> execution (except that on some LNT runners we're multisampling, so
> >> >> it's slower)
> >> >>
> >> >> > When I set up some tests to run on ARM I have done both direct and
> >> >> > multi-step, to make sure they were generating the same code and in
> >> >> > many
> >> >> > cases I found that the order in which the passes were executed was
> >> >> > breaking
> >> >> > some tests.
> >> >> >
> >> >> > We managed to get the EDG bridge to set it up in the same way as
> the
> >> >> > multi-pass would, so we would get similar results, but it doesn't
> >> >> > seem
> >> >> > to be
> >> >> > the case with clang.
> >> >> >
> >> >> > cheers,
> >> >> > --renato
> >> >
> >> >
> >
> >
>
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