[llvm-dev] [cfe-dev] Testing Best Practices/Goals (in the context of compiler-rt)

Xinliang David Li via llvm-dev llvm-dev at lists.llvm.org
Wed Feb 10 14:33:35 PST 2016

On Wed, Feb 10, 2016 at 2:11 PM, Justin Bogner via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> David Blaikie via cfe-dev <cfe-dev at lists.llvm.org> writes:
> > Recently had a bit of a digression in a review thread related to some
> tests
> > going in to compiler-rt (
> >
> http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160208/330759.html
> > ) and there seems to be some disconnect at least between my expectations
> > and reality. So I figured I'd have a bit of a discussion out here on the
> > dev lists where there's a bit more visibility.
> >
> > My basic expectation is that the lit tests in any LLVM project except the
> > test-suite are targeted tests intended to test only the functionality in
> > the project. This seems like a pretty well accepted doctrine across most
> > LLVM projects - most visibly in Clang, where we make a concerted effort
> not
> > to have tests that execute LLVM optimizations, etc.
> >
> > There are exceptions/middle ground to this - DIBuilder is in LLVM, but
> > essentially tested in Clang rather than writing LLVM unit tests. It's
> > somewhat unavoidable that any of the IR building code (IRBuilder,
> > DIBuilder, IR asm printing, etc) is 'tested' incidentally in Clang in
> > process of testing Clang's IR generation. But these are seen as
> incidental,
> > not intentionally trying to cover LLVM with Clang tests (we don't add a
> > Clang test if we add a new feature to IRBuilder just to test the
> IRBuilder).
> >
> > Another case with some middle ground are things like linker tests and
> > objdump, dwarfdump, etc - in theory to isolate the test we would checkin
> > binaries (or the textual object representation lld had for a while, etc)
> to
> > test those tools. Some tests instead checkin assembly and assemble it
> with
> > llvm-mc. Again, not to cover llvm-mc, but on the assumption that llvm-mc
> is
> > tested, and just using it as a tool to make tests easier to maintain.
> >
> > So I was surprised to find that the compiler-rt lit tests seem to diverge
> > from this philosophy & contain more intentional end-to-end tests (eg:
> > adding a test there when making a fix to Clang to add a counter to a
> > function that was otherwise missing a counter - I'd expect that to be
> > tested in Clang and that there would already be coverage in compiler-rt
> for
> > "if a function has a counter, does compiler-rt do the right thing with
> that
> > counter" (testing whatever code in compiler-rt needs to be tested)).
> >
> > Am I off base here? Are compiler-rt's tests fundamentally different to
> the
> > rest of the LLVM project? Why? Should they continue to be?
> I think there's a bit of grey area in terms testing the runtime -
> generally it's pretty hard to use the runtime without a fairly
> end-to-end test, so tests of the runtime often end up looking pretty
> close to an end-to-end test.
> That said, I don't think that should be used as an excuse to sneak
> arbitrary end-to-end tests into compiler-rt. We should absolutely write
> tests in clang and llvm that we're inputting what we expect to the
> runtime and try to keep the tests in compiler-rt as focused on just
> exercising the runtime code as possible.

Yes, we should not use compiler-rt tests as an excuse of not adding
clang/LLVM test. The latter should always be added if possible -- they are
platform independent and is the first level of defense.  runtime test's
focus is also more on the runtime lib itself and interaction between
 runtime, compiler, binutils and other tools.


> IIUC, the correct place for integration tests in general is somewhere
> like test-suite, but I think it's a bit intimidating to some people to
> add new tests there (Are there docs on this?). I suspect some of the
> profiling related tests in compiler-rt are doing a bit much and should
> graduate to a spot in the test-suite (but I don't have time to volunteer
> to do the work, unfortunately).
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