[llvm-dev] RFC: Add bitcode tests to test-suite

Thu Feb 18 08:19:29 PST 2016

On Thu, Feb 18, 2016 at 6:54 AM, Hal Finkel via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi Chandler, et al.,
>
> While this proposal to put IR into the test suite technically
> non-problematic, I've convinced myself that this is a suboptimal direction
> for the LLVM project. Here's what I think would be better:
>
>  - We create a test-suite/Frontends directory, and open this directory to
> actively-maintained external frontends, subject to the following
> restrictions:
>
>    - The frontend must be actively maintained, and the project must agree
> to actively maintain the test-suite version
>    - The frontend must use the LLVM API (either C or C++) - no printing
> textual IR
>    - The frontend must have no significant (non-optional) dependencies
> outside of LLVM itself, or things on which LLVM itself depends
>    - The frontend must have regression tests and benchmarks/correctness
> tests providing significant coverage of the frontend and its associated
> code generation
>
> Here's the quid pro quo:
>
>    - The LLVM community gains additional testing coverage (which we
> definitely need)
>    - The LLVM community gains extra insight into how its APIs are being
> used (hopefully allowing us to make more-informed decisions about how to
> update them)
>
>    - The frontend gains free API updates
>    - The frontend's use of LLVM will be more stable
>
> This involves extra work for everybody, but will help us all deliver
> higher-quality products. Plus, given the constant discussions about the
> difficulty for external projects to follow API updates, etc., this is a
> good way to help address those difficulties.
>

Given the extra cost it incurs on LLVM developers changing APIs, this seems
like a problematic tradeoff/not necessarily good. LLVM moves quickly
because it can/it is beneficial, this causes pain/cost to out-of-tree
projects. Moving that cost to LLVM would simply make LLVM move more
slowly/API changes would be made less frequently. I'm not sure that's the
right tradeoff - the LLVM project would end up paying the cost of the
external project but not gaining the advantages of the project being part
of the LLVM Project umbrella (the developers wouldn't be contributing back
to the LLVM community/codebase, etc as they would if it were more of a
Clang, or LLD, etc).

>
> The fact that Halide will provide extra coverage of our vector code
> generation (aside from whatever we happen to produce from our
> autovectorizers), and our JIT infrastructure, makes it a good candidate for
> this. Intel's ispc, POCL, (maybe whatever bit of Mesa uses LLVM), etc.
> would also be natural candidates should the projects be interested.
>
> Thanks again,
> Hal
>
> ----- Original Message -----
> > From: "Chandler Carruth" <chandlerc at google.com>
> > To: "Hal Finkel" <hfinkel at anl.gov>, "Alina Sbirlea" <
> alina.sbirlea at gmail.com>
> > Cc: "llvm-dev" <llvm-dev at lists.llvm.org>
> > Sent: Wednesday, February 17, 2016 9:34:24 PM
> > Subject: Re: [llvm-dev] RFC: Add bitcode tests to test-suite
> >
> >
> > Some perhaps relevant aspects that make testing users of LLVM like
> > Halide challenging:
> >
> >
> > Halide uses the LLVM C++ APIs, but there isn't a good way to
> > lock-step update it. So if we were to directly test Halide, it
> > wouldn't link against the new LLVM.
> >
> >
> > Practically speaking though, the LLVM IR generated by Halide should
> > continue to work with newer LLVM optimizations and code generation.
> > So the idea would be to snapshot the IR in bitcode (which is at
> > least reasonably stable) so that we could replay the tests as LLVM
> > changes. We can freshen the bitcode by re-generating it periodically
> > so it doesn't drift too far from what Halide actually uses.
> >
> >
> > The interesting questions IMO are:
> >
> >
> > 1) Are folks happy using bitcode as the format here? I agree with Hal
> > that it should be easy since Clang will actually Do The Right Thing
> > if given a bitcode input.
> >
> >
> > 2) Are folks happy with non-execution tests in some cases? I think
> > Alina is looking at whether we can get a runtime library that will
> > allow some of these to actually execute, but at least some of the
> > tests are just snap-shots of a JIT, and would need the full Halide
> > libraries (and introspection) to execute usefully.
> >
> >
> > -Chandler
> >
> >
> > On Wed, Feb 17, 2016 at 7:25 PM Hal Finkel via llvm-dev <
> > llvm-dev at lists.llvm.org > wrote:
> >
> >
> >
> >
> >
> >
> >
> >
> > From: "Alina Sbirlea via llvm-dev" < llvm-dev at lists.llvm.org >
> > To: "llvm-dev" < llvm-dev at lists.llvm.org >
> > Sent: Wednesday, February 17, 2016 7:25:17 PM
> > Subject: [llvm-dev] RFC: Add bitcode tests to test-suite
> >
> >
> >
> >
> >
> >
> > Hi all,
> >
> >
> > TL;DR: Add *.bc to test-suite; llc *.bc; run some.
> >
> >
> >
> > We would like to propose adding bitcode tests to the llvm test-suite.
> >
> >
> > Recent LLVM bugs [2-4] prompted us to look into upstreaming a subset
> > of the tests the Halide library [1] is running and we'd like the
> > community's feedback on moving forward with this.
> >
> >
> >
> > Halide uses LLVM and can generate bitcode, but we cannot add C++
> > tests to test-suite without including the library itself.
> > This proposal is also potentially useful for other cases where there
> > is no C++ front-end.
> >
> >
> > As a first step we are interested in adding a set of correctness
> > tests, for testing the IR without running the tests. Since these
> > tests are generated, they are not instrumented like the .ll files in
> > trunk, however we believe checking that llc runs without errors is
> > still useful.
> > The bitcode files for Halide may also be large, so including them as
> > regression tests is not an option. If the smaller tests are found to
> > be valuable or covering cases no other tests cover, we can
> > instrument them and move them into the llvm trunk further along, but
> > that is not the goal of this proposal.
> > In addition, we're not sure whether the format for the tests should
> > be .ll or .bc, we're open to either.
> >
> >
> > After this first step, we're interested in upstreaming bitcode tests
> > and also running them.
> > We are very interested in tests for multiple architectures, aarch64
> > in particular, since this is where we have seen things break. This
> > may motivate adding .ll files rather than .bc in order to include
> > the "RUN:" target.
> > Where would these tests reside and with what directory structure?
> > (similar to test/CodeGen?)
> >
> >
> > Suggestion on what's the best approach for extending the test-suite
> > framework for this proposal are more than welcome.
> >
> >
> >
> > We already have architecture-specific tests in the test suite (e.g.
> > SingleSource/UnitTests/Vector/{SSE,Altivec,etc.}, and Clang can deal
> > with IR inputs. I suppose you need to compile some corresponding
> > runtime library, but this does not seem like a big deal either.
> > Mechanically, I don't see this as particularly complicated. I think
> > the real question is: Is this the best way to have a kind of 'halide
> > buildbot' that can inform the LLVM developer community?
> >
> > -Hal
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > This is just the high-level overview to start off the discussion, I'm
> > sure there are many more aspects to touch on. Looking forward to
> > your feedback!
> >
> >
> >
> > Thanks,
> > Alina
> >
> >
> > [1] http:// halide -lang.org/
> > [2] Broken: r259800 => Fixed: r260131
> > [3] Broken: r260569 => Fixed: r260701
> >
> > [4] https://llvm.org/bugs/show_bug.cgi?id=26642
> >
> >
> >
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
> >
> >
> >
> >
> > --
> >
> > Hal Finkel
> > Assistant Computational Scientist
> > Leadership Computing Facility
> > Argonne National Laboratory
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
>
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
> _______________________________________________
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> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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