[llvm-dev] Help with a pass

[Alberto Barbaro via llvm-dev]

Thanks John,
All clear now. Is it worthy to open a bug issue?

Thanks

On Tue, Nov 20, 2018, 14:59 John Brawn <John.Brawn at arm.com wrote:

> There’s two things going on here:
>
>
>
> Firstly, extension points interact in a slightly odd way with optimization
> levels:
>
> * At -O0 the only extension points used are EP_EarlyAsPossible and
> EP_EnabledOnOptLevel0
>
> * At -O1 and higher all extension points are used *except*
> EP_EnabledOnOptLevel0
>
> so when you’re not seeing the crash it’s because you’re using an
> optimization level (probably -O0  because that’s
>
> the default) where the extension point you’re using isn’t used.
>
>
>
> Secondly, CGSCC passes can only be added to a GCSCC pass manager. If you
> use a debug build of clang then the
>
> crash becomes an assertion failure which (somewhat) tells you this:
>
> CallGraphSCCPass.cpp:575: virtual void
> llvm::CallGraphSCCPass::assignPassManager(llvm::PMStack&,
> llvm::PassManagerType): Assertion `!PMS.empty() && "Unable to handle Call
> Graph Pass"' failed.
>
> From some experimentation it looks like it’s only EP_EarlyAsPossible where
> we get this error, because (looking
>
> at PassManagerBuilder::populateFunctionPassManager) that extension point
> uses a Function Pass Manager
>
> whereas all the others look like they use a Module Pass Manager.
>
>
>
> John
>
>
>
> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of *Alberto
> Barbaro via llvm-dev
> *Sent:* 16 November 2018 18:34
> *To:* llvm-dev at lists.llvm.org
> *Subject:* [llvm-dev] Help with a pass
>
>
>
> Hi all,
>
> I was able to create a pass following [1]. Now goal is amend the pass and
> try to dump the call graph. I think I have properly amended the source
> extending my pass from CallGraphSCCPass but unfortunately every time I run
> it, it crashes. I tried with llvm-6 and llvm-7. I notice that if I change
> EP_EarlyAsPossible to anything else it does not crash but I don't see the
> expected string printed by the runOnSCC.
>
>
>
> Could you help me to solve this problem? How should I create the pass?
>
>
>
> Thanks for your time
>
>
>
> [1] https://www.cs.cornell.edu/~asampson/blog/llvm.html
>
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