aeubanks 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
----------------
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).
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D93656/new/
https://reviews.llvm.org/D93656
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