[llvm-dev] Out-of-tree AA pass used from ModulePass

[Stephan Diestelhorst via llvm-dev]

(Please keep me in CC, not sure my subscription request has made it through yet)
Hi all,

I am building a fairly extensive set of compiler passes out-of-tree with LLVM, and this all works nicely, except for tying my custom AA pass MyAA into the overall AA aggregator via AAResultsWrapper. As far as I can see, the ExternalAAWrapper does what I want and allows me to add an out-of-tree AA pass to the list of passes that is consulted when my other passes (let's say MyFuncPass) need an alias analysis result, by having registered a call-back in ExternalAAWrapper that will add MyAAResult into llvm::AAResult, which then gets consulted in AA queries if needed. This works for now (with some hacks).

The problem is, however, when I convert MyFuncPass to a module pass, and I am then trying to get aa results for my functions.  The problem is that the call-back I registered (I see that happening!) with ExternalAAWrapper is never being run, so my AA results are not added to the mix.  I am using opt and the legacy pass managers, and I am struggling to understand how this should be used correctly, and why the call-back is not executed in time when turning my pass into a ModulePass.

I am getting my aa results via getAnalysis<AAResultsWrapperPass>().getAAResults() in MyFuncPass, and with getAnalysis<AAResultsWrapperPass>(f).getAAResults() with f being the function I am currently looking into in the ModulePass.

I am not really sure which passes I must specify with addRequired(..) or on the command line and it seems the documentation around AA in general and external AA specifically is somewhat outdated / sparse.

Does this fairly high-level description ring any bells?  My code is pretty wild at this point, so it is not trivial to create a simple example, but I can do it if it would be helpful here.  Further, for various reasons (started this project a fair while ago) I am still on LLVM 8, but AFAICS, not much has changed in this area. That said, I don't have a great understanding how the whole (legacy) pass manager piece hangs together.

Thanks,
  Stephan
--
Stephan Diestelhorst
System Architect
Xilinx - Data Center Group
Cambridge, UK

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