llvm dev - Nov 2018 - 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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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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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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