[llvm-dev] Pass reduction with new PM

Mon Aug 2 02:17:41 PDT 2021

I firmly believe that something that almost works is a lot better than nothing that certainly won’t work at all so I suggest we go for the short term hack as you described.

I can try giving it a go but please provide all the details you have on that option.

So as far as I can see getting pass names using `PIC->getPassNameForClassName(PassID)` seems straight forward. Looks like we can get printouts when a PassManager and PassAdopter starts but I cannot see any callbacks that would be called when it is finished so maybe that needs to be added to be able to get the nesting right.

I think that reduction of the passes string can be handled by an external tool and for starters I would be happy to do it manually.

br
-Markus

From: Arthur Eubanks <aeubanks at google.com>
Sent: den 30 juli 2021 20:54
To: Markus Lavin <markus.lavin at ericsson.com>
Cc: llvm-dev <llvm-dev at lists.llvm.org>
Subject: Re: [llvm-dev] Pass reduction with new PM

There still is nothing like bugpoint's pass list reduce for the new PM.

The issue is that ideally we'd be able to map a pass pipeline to the string version of it. But we can't really do that right now. We could attempt to do that, but a generated argument list won't be exact since passes added via code (e.g. PassManagerBuilder/PassBuilder.cpp) often have parameters that can't be represented via opt arguments. Maybe getting an approximate textual representation of the pipeline is good enough for some cases? But that doesn't seem ideal.
We could also go down the route of making all pipelines representable via text, but that's a non-trivial project.

Note that even the legacy PM has this problem, and I've heard that this has bitten people in the past.

Perhaps as a short term hack, we could get an approximation of the pipeline by hacking PrintPassInstrumentation to print the textual name of each pass that's run via `PIC->getPassNameForClassName(PassID)` (like PrintIRInstrumentation). Then run `opt -debug-pass-manager with that hacked up version of PrintPassInstrumentation. We'd also need another version of -debug-pass-manager that prints adaptors/pass managers but doesn't print analyses. We'd run `opt` over a file with one function that contains one loop, e.g. the IR in new-pm-defaults.ll. Then cleanup the output of -debug-pass-manager with proper pass nesting.

Or of course you could attempt to manually recreate the proper textual representation by looking at PassBuilder.cpp.

Then we'd need something that reduces the textual pass pipeline.

Let me know if you'd like more details.

On Fri, Jul 30, 2021 at 12:25 AM Markus Lavin via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
Hi,

Right now I am trying to analyze a bug that appears with new PM pipeline as follows

$ opt -enable-new-pm=1 -disable-basic-aa -tbaa -O1 -o /dev/null reduced.ll

the crashing pass is LICM but simply exporting IR before that pass and then running just that pass does not seem to capture enough state to reproduce the problem.

So here one would either want bugpoint to help automatically reduce the pass list or simply use -debug-pass=Arguments and do it manually but as I understand it neither of those options work with the new PM.

This has already been brought up in [llvm-dev] How to get from "opt -O3" to "opt <a-single-pass>" with the new PM?<https://protect2.fireeye.com/v1/url?k=f586695a-aa1d5188-f58629c1-866132fe445e-6110e351e37b7346&q=1&e=2ba6e21d-2217-4037-91d5-479923a5d53a&u=https%3A%2F%2Flists.llvm.org%2Fpipermail%2Fllvm-dev%2F2021-March%2F148994.html>
Has there been any progress since then?

br
Markus

_______________________________________________
LLVM Developers mailing list
llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev<https://protect2.fireeye.com/v1/url?k=6737c3b4-38acfb66-6737832f-866132fe445e-1cee692663522fcb&q=1&e=2ba6e21d-2217-4037-91d5-479923a5d53a&u=https%3A%2F%2Flists.llvm.org%2Fcgi-bin%2Fmailman%2Flistinfo%2Fllvm-dev>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20210802/bb6e7285/attachment.html>