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

[Chandler Carruth via llvm-dev]

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
>
>
>
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>
>
>
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
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