[llvm-dev] optnone/skipping passes in the new pass manager

[Chen, Yuanfang via llvm-dev]

I think adding a before-pass callback checking optnone to PassInstrumentation of NPM should suffice for the `skipFunction` alone. However, it is closely related to opt-bisect which makes it more complicated.

This was the previous discussion.
http://lists.llvm.org/pipermail/llvm-dev/2018-September/126477.html


________________________________________
From: llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Arthur Eubanks via llvm-dev <llvm-dev at lists.llvm.org>
Sent: Sunday, June 7, 2020 4:58 PM
To: llvm-dev
Subject: [llvm-dev] optnone/skipping passes in the new pass manager

Looking through some of the remaining test failures under the new pass manager, I've narrowed down one of the failures in GWPAsan(!) to the fact that the new pass manager doesn't properly skip passes like the old pass manager. For example, when a function is marked optnone, or when using https://llvm.org/docs/OptBisect.html.

Lots of passes (e.g. SROA) will do the following under the legacy pass manager:

  bool runOnFunction(Function &F) override {
    if (skipFunction(F))
      return false;
    // do pass
  }

What's the right way to proceed with this? There are 50-100 calls to skipFunction() in legacy passes. This doesn't even account for other types of IR units, like skipModule(Module&).

I suppose it's possible to manually go in and add in the same check in the new passes, but that seems tedious (and how do you test that at scale? clearly there aren't many tests for it right now since check-llvm passes under the new pass manager). An alternative of skipping passes at the pass manager level would require marking each pass as necessary/optional (I think...).