[llvm-dev] Orc JIT Layering

[David Blaikie via llvm-dev]

To clarify, I'm not sure JITSymbol should be in llvmSupport, but that it's
the only place it can be right now that would be correct. Maybe there's
some other layering changes (not necessarily introducing a new library, but
possibly changing other dependency edges, etc) - but maybe there's already
some JIT Stuff in llvmSupport and that's where it should go. It's a simple
enough header/wouldn't come at a great cost to include it in Support.

On Wed, Mar 3, 2021 at 1:51 AM Stefan Gränitz <stefan.graenitz at gmail.com>
wrote:

> Hi David
>
> Thanks for the details. Yes, the layering issue is something we should
> take care of soon. It also makes trouble for the modules build (see:
> https://reviews.llvm.org/D95747).
>
> I think we should split up the JITSymbol.h and move JITTargetAddress into
> OrcShared. What remains would be the JITSymbol class. Moving this one to
> Support sounds like a nice solution to me.
>
> However, we have a similar situation with the GDB JIT interface
> declarations. They should have their own header, yes, but where would we
> put it? Support too? Not sure about it. Having the definition only in
> OrcTargetProcess would be acceptable IMHO. The only alternative seems to be
> an entirely new library (as discussed in the review
> https://reviews.llvm.org/D97339).
>
> What do you think?
>
> @Peter, @Nico: I've noticed your post-review comments. I will have a look
> tonight (~10h from now).
>
> Best,
> Stefan
>
> On 03/03/2021 04:57, David Blaikie wrote:
>
> Seems one of the latest Orc changes (
> https://github.com/llvm/llvm-project/commit/99a6d003edbe97fcb94854547276ffad3382ec1d
> ) while not itself changing/breaking the layering in LLVM's own build, it
> has revealed some pre-existing problems with the layering that we'd worked
> around at Google in a way that isn't viable after this recent change.
>
> One immediate/easily observed issue: lib/ExecutionEngine's CMakeLists.txt
> says it depends on OrcTargetProcess, but OrcTargetProcess includes
> lib/ExecutionEngine/JITSymbol.h
>
> The only common dependency for all the uses of JITSymbol.h seems to be
> llvm/Support (ie: without introducing new dependencies or new libraries,
> JITSymbol.h would need to be moved to llvm/Support to fix this particular
> dependency cycle/issue)
>
> We do have a bunch of other workarounds for Orc layering in the Google
> internal build system too - so perhaps I can enumerate some/all of the
> issues here, as it might be best to take a holistic approach to fixing
> these issues.
>
> Let's see what I can document/figure out...
>
> ExecutionEngine/Orc -> ExecutionEngine
> ExecutionEngine/Interpreter -> ExecutionEngine
> ExecutionEngine/RuntimeDyld -> ExecutionEngine
> ExecutionEngine/IntelJITEvents -> ExecutionEngine
> ExecutionEngine/OProfileJIT -> ExecutionEngine
> ExecutionEngine/PerfJITEvents -> ExecutionEngine
> ExecutionEngine/MCJIT -> ExecutionEngine
>
> And there's actually no #includes in ExecutionEngine that reference those
> libraries, so that's pretty good.
>
> It is this CMakeLists.txt dependency from ExecutionEngine to
> OrcTargetProcess. Which happens without a #include:
>
> $ grep -r "void __jit_debug_register_code" llvm/
>
> llvm/lib/ExecutionEngine/GDBRegistrationListener.cpp:  extern "C" *void
> __jit_debug_register_code*();
>
> llvm/lib/ExecutionEngine/Orc/TargetProcess/JITLoaderGDB.cpp:LLVM_ATTRIBUTE_NOINLINE
> *void __jit_debug_register_code*() {
>
> Would be better if this wasn't declared arbitrarily (instead, if it was
> declared in a header and defined as usual, the circular dependence would be
> more clear, I think?) - but either way, the circular dependency needs to be
> fixed.
>
> - Dave
>
>
>
> -- https://flowcrypt.com/pub/stefan.graenitz@gmail.com
>
>
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