hoy added inline comments.
================
Comment at: clang/test/CodeGen/unique-internal-linkage-names.cpp:48-49
+// LPIPELINE: Unique Internal Linkage Names
+// NPIPELINE: Running pass: UniqueInternalLinkageNamesPass
// PLAIN: @_ZL4glob = internal global
----------------
dblaikie wrote:
> hoy wrote:
> > dblaikie wrote:
> > > aeubanks wrote:
> > > > dblaikie wrote:
> > > > > hoy wrote:
> > > > > > aeubanks wrote:
> > > > > > > hoy wrote:
> > > > > > > > aeubanks wrote:
> > > > > > > > > dblaikie wrote:
> > > > > > > > > > hoy wrote:
> > > > > > > > > > > dblaikie wrote:
> > > > > > > > > > > > Does this test validate the new behavior? (ie: does
> > > > > > > > > > > > this test fail without the LLVM changes and pass with
> > > > > > > > > > > > it) Not that it necessarily has to - since Clang isn't
> > > > > > > > > > > > here to test the LLVM behavior - perhaps this test is
> > > > > > > > > > > > sufficient in Clang to test that the code in
> > > > > > > > > > > > BackendUtil works to enable this pass.
> > > > > > > > > > > >
> > > > > > > > > > > > This could possibly be staged as independent commits -
> > > > > > > > > > > > adding the LLVM functionality in one commit, which
> > > > > > > > > > > > would be a no-op for Clang because it wouldn't be
> > > > > > > > > > > > setting PTO.UniqueLinkageNames - then committing the
> > > > > > > > > > > > Clang change that would remove the custom pass addition
> > > > > > > > > > > > and set PTO.UniqueLinkageNames - and then it'd probably
> > > > > > > > > > > > be reasonable to have this test be made a bit more
> > > > > > > > > > > > explicit (testing the pass manager structure/order) to
> > > > > > > > > > > > show that that Clang change had an effect: Moving the
> > > > > > > > > > > > pass to the desired location in the pass pipeline.
> > > > > > > > > > > This is a good question. No, this test does not validate
> > > > > > > > > > > the pipeline change on the LLVM side, since Clang
> > > > > > > > > > > shouldn't have knowledge about how the pipelines are
> > > > > > > > > > > arranged in LLVM. As you pointed out, the test here is to
> > > > > > > > > > > test if the specific pass is run and gives expected
> > > > > > > > > > > results.
> > > > > > > > > > >
> > > > > > > > > > > Thanks for the suggestion to break the Clang changes and
> > > > > > > > > > > LLVM changes apart which would make the testing more
> > > > > > > > > > > specific. The pipeline ordering could be tested with a
> > > > > > > > > > > LLVM test but that would require a LLVM switch setup for
> > > > > > > > > > > UniqueLinkageNames and I'm not sure there's a need for
> > > > > > > > > > > that switch except for testing.
> > > > > > > > > > > No, this test does not validate the pipeline change on
> > > > > > > > > > > the LLVM side, since Clang shouldn't have knowledge about
> > > > > > > > > > > how the pipelines are arranged in LLVM.
> > > > > > > > > >
> > > > > > > > > > "ish" - but Clang should have tests for changes to Clang,
> > > > > > > > > > ideally. Usually they can simply be testing LLVM's IR
> > > > > > > > > > output before it goes to LLVM for optimization/codegen -
> > > > > > > > > > but for features that don't have this serialization
> > > > > > > > > > boundary that makes testing and isolation clear/simple, it
> > > > > > > > > > becomes a bit fuzzier.
> > > > > > > > > >
> > > > > > > > > > In this case, there is a clang change - from adding the
> > > > > > > > > > pass explicitly in Clang, to setting a parameter about how
> > > > > > > > > > LLVM will add the pass, and it has an observable effect.
> > > > > > > > > > One way to test this change while isolating the Clang test
> > > > > > > > > > from further changes to the pipeline in LLVM, would be to
> > > > > > > > > > test that the pass ends up somewhere in the LLVM-created
> > > > > > > > > > part of the pass pipeline - the parts that you can't get to
> > > > > > > > > > from the way the original pass addition was written in
> > > > > > > > > > Clang. At least I assume that's the case/what motivated the
> > > > > > > > > > change from adding it in Clang to adding it in LLVM?
> > > > > > > > > >
> > > > > > > > > > eg: if LLVM always forms passes {x, y, z} and Clang is able
> > > > > > > > > > to add passes before/after, say it always adds 'a' before
> > > > > > > > > > and 'b' after, to make {a, x, y, z, b} - and this new pass
> > > > > > > > > > u was previously added at the start to make {u, a, x, y, z,
> > > > > > > > > > b} but now needs to go in {a, x, y, u, z, b} you could test
> > > > > > > > > > that 'u' is after 'a' and before 'b', or between 'x' and
> > > > > > > > > > 'z', etc. If there's some other more clear/simple/reliable
> > > > > > > > > > marker of where the LLVM-created passes start/end in the
> > > > > > > > > > structured dump, that'd be good to use as a landmark to
> > > > > > > > > > make such a test more robust. If there's some meaningful
> > > > > > > > > > pass that this pass always needs to go after - testing that
> > > > > > > > > > might be OK, even if it's somewhat an implementation detail
> > > > > > > > > > of LLVM - whatever's likely to make the test more legible
> > > > > > > > > > and more reliable/resilient to unrelated changes would be
> > > > > > > > > > good.
> > > > > > > > > >
> > > > > > > > > > > As you pointed out, the test here is to test if the
> > > > > > > > > > > specific pass is run and gives expected results.
> > > > > > > > > >
> > > > > > > > > > If that's the case, this test could be committed
> > > > > > > > > > standalone, before any of these other changes?
> > > > > > > > > >
> > > > > > > > > > > The pipeline ordering could be tested with a LLVM test
> > > > > > > > > > > but that would require a LLVM switch setup for
> > > > > > > > > > > UniqueLinkageNames and I'm not sure there's a need for
> > > > > > > > > > > that switch except for testing.
> > > > > > > > > >
> > > > > > > > > > That's OK, the entire 'opt' tool and all its switches only
> > > > > > > > > > exist for testing. eg:
> > > > > > > > > > https://github.com/llvm/llvm-project/blob/master/llvm/tools/opt/NewPMDriver.cpp#L284
> > > > > > > > > The point of this change is that
> > > > > > > > > UniqueInternalLinkageNamesPass should run before
> > > > > > > > > SampleProfileProbePass. That must make a difference in the
> > > > > > > > > output of something like `clang -emit-llvm -O1`, right? Maybe
> > > > > > > > > we can add a new clang test that checks for that new change
> > > > > > > > > in IR, no need to check -fdebug-pass-manager. (I'm not
> > > > > > > > > familiar with the passes, correct me if I'm wrong)
> > > > > > > > Maybe we can just keep the Clang test unchanged? What do you
> > > > > > > > think? Since it's basically testing the command line switch
> > > > > > > > `-funique-internal-linkage-names` works as expected, i.e,
> > > > > > > > giving unique linkage names, it probably shouldn't care where
> > > > > > > > the renaming happens exactly. Checking the pass order sounds a
> > > > > > > > job to LLVM. I'll make the LLVM test do that.
> > > > > > > >
> > > > > > > >
> > > > > > > > > The point of this change is that
> > > > > > > > > UniqueInternalLinkageNamesPass should run before
> > > > > > > > > SampleProfileProbePass.
> > > > > > > >
> > > > > > > > Yeah, that's the point. We should probably make an LLVM test
> > > > > > > > for it instead of a Clang test.
> > > > > > > An LLVM test sounds good, though you'll need a new cl::opt that
> > > > > > > the new option in PipelineTuningOptions defaults to (like other
> > > > > > > options in PipelineTuningOptions).
> > > > > > Yeah, I was thinking about that too. I will also need a switch to
> > > > > > trigger SampleProfileProbePass, like the exiting
> > > > > > `-new-pm-debug-info-for-profiling`.
> > > > > I'm a bit confused by this thread of discussion.
> > > > >
> > > > > Some fairly fundamental test architecture issues in the LLVM project:
> > > > > Code changes within a project should be tested within that project.
> > > > > Ideally they should test so as narrowly as possible so as not to
> > > > > produce failures due to unrelated changes.
> > > > >
> > > > > This is usually fairly easy with anything in IR (test that Clang
> > > > > produces certain IR, test that optimization passes optimize that IR
> > > > > in certain ways, test that certain IR produces certain machine code,
> > > > > etc) - but harder with things that are represented only in API
> > > > > surface area (ie: there's no serialization of PipelineTuningOptions
> > > > > between Clang and LLVM - if there was, we could test that given a
> > > > > clang command line argument, the PTO has a certain property - then
> > > > > separately in LLVM we'd test that, given that PTO, a certain pass
> > > > > pipeline is constructed with the relevant features). In the absence
> > > > > of a serialization layer, we make a best effort in some way or
> > > > > another.
> > > > >
> > > > > I think the best effort for a clang test for this clang change would
> > > > > be to dump the pass pipeline and ensure it has the property that's
> > > > > important - whatever property wasn't true before this change and is
> > > > > being made true by this change. Such as, as @aeubanks said, testing
> > > > > that UniqueInternalLinkageNamesPass comes before
> > > > > SampleProfileProbePass.
> > > > >
> > > > > I think it is important that this is tested in Clang and separately
> > > > > that the functionality is tested in LLVM (by exposing the PTO
> > > > > parameter through opt, like other PTO parameters), probably in a
> > > > > similar manner (testing that given this PTO parameter, the pass
> > > > > pipeline has a certain shape). All of that separate from testing the
> > > > > pass itself does certain things when it is run (& that testing would
> > > > > be done in isolation - just running the specified pass).
> > > > I'm not a fan of clang tests checking the output of
> > > > -debug-pass-manager, it's checking implementation details that clang
> > > > doesn't control. I'd prefer clang to just check that the pass ran
> > > > somehow by examining the output IR given the clang cc1 flag. For
> > > > example, maybe some function has `__uniq` in the name (maybe this test
> > > > already checks something along these lines). Checking the exact PTO
> > > > doesn't seem important. And for this change IMO clang doesn't need to
> > > > test that some passes ran in some specific order, that's now an LLVM
> > > > implementation detail.
> > > >
> > > > The specifics of running UniqueInternalLinkageNamesPass before
> > > > SampleProfileProbePass is now an LLVM thing, so an LLVM test should
> > > > test that, whether it's checking -debug-pass-manager, or even better,
> > > > checking the IR for certain properties.
> > > There's certainly no great answers here, imho. It's going to be tradeoffs
> > > for sure.
> > >
> > > Clang tests executing the whole LLVM pipeline and checking the right
> > > answer out the otehr end means a lot more code under test - a lot more
> > > places that can have bugs that cause this test to fail that aren't just
> > > the one line in Clang the test is intended to test (it's not meant to
> > > test the LLVM functionality, that is tested in LLVM).
> > >
> > > Clang does control some aspects of the pass pipeline - in this case
> > > moving the pass being added by clang explicitly, to asking LLVM to do it.
> > > Admittedly, yeah, no there's other aspects of implementation detail -
> > > Clang doesn't need to have any knowledge of specific pass names, or that
> > > this functionality is implemented by a pass.
> > >
> > > All that said, as much as I don't find it great (tradeoffs for all
> > > answers here), yeah, I'm not going to veto an end-to-end test. I've
> > > certainly written them in the past when there really wasn't any other
> > > option (-fdebug-types-section, if I recall - MC flag with no observable
> > > effect until assembly is generated... no pass pipeline differences, etc
> > > (actually, maybe I just didn't test that at all, I forget which way I
> > > went - not ideal either way, to be sure)).
> > Thanks for all the discussion and suggestions here. I think we all agree on
> > making a LLVM test that checks the pipeline order as well as the output of
> > that particular pass. Regarding the Clang test, since there's no for-sure
> > answer, I'm inclined to leave it as is, i.e, without checking the exact
> > PTO. This sounds a bit more robust to me since we'd like to isolate LLVM
> > changes from Clang testing failures.
> Seems like - if I'm understanding this correctly: "leave it as is" doesn't
> seem sufficient to me: Any test changes included with this patch should fail
> without it and pass with the code change (ie: demonstrate that the code
> change had a/the desired effect)
>
> If this test change doesn't do that, it's both not suitable to include in
> this patch (since it's an unrelated change) and insufficient - because the
> production code change is untested.
The changes in the Clang test have been undone, if you look at the latest
iteration which is a pure llvm patch now. The code change in Clang will be in a
separate patch.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D93656/new/
https://reviews.llvm.org/D93656
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