[llvm-dev] [RFC][NewPM] Migrating tests from `opt -foo` to `opt -passes=foo`

[Arthur Eubanks via llvm-dev]

`opt -pass` relies on the global registry of legacy passes, which we should
really get rid of at some point. It might be possible to do something
similar with a cl::opt that uses the new PM PassBuilder parsing, but that
would end up being super hacky. `opt -pass` doesn't really fit the design
of the new PM.

IMO `opt -passes=foo` is much clearer than `opt -foo` and is not much
longer to type (it's what I use now, even for simple things). I remember
when I started working on LLVM, the `opt -foo` syntax was confusing,
especially when there were multiple passes and they were interleaved on the
command line with other flags.

On Mon, Jul 5, 2021 at 10:56 AM Philip Reames <listmail at philipreames.com>
wrote:

> Can I ask a basic question?  Given we've separated the interface from the
> choice of pass manager, why are we removing the "-pass" interface at all?
> Is there some non-trivial amount of maintenance needed to keep that working?
>
> Personally, I find the -pass-name interface much easier to work with for
> simple adhoc testing than the -passes version.
>
> I can definitely see the case for dropping testing of old-pm + pass
> combinations, but at this point, that's less about the command line and
> more about removing -enable-new-pm=0 tests.  There's also maybe an argument
> that we should spell the command line only one way in testing, but that's
> different than removing the command line parsing.
>
> Philip
> On 6/28/21 6:33 PM, Arthur Eubanks via llvm-dev wrote:
>
> Now that the new PM has been the default for the optimization pipeline for
> a while, I'd like to start thinking about next steps. Not quite deprecating
> the legacy PM for the optimization pipeline yet, since we should wait for
> the next LLVM release. But one thing we can start doing is cleaning up lit
> tests that use opt.
>
> There's been confusion over exactly how the -passes= parsing works, so
> I've updated https://llvm.org/docs/NewPassManager.html (or rather just
> the sources, seems like the webpage hasn't updated yet) with some details.
>
> For background, `opt -foo` is currently already translated to `opt
> -passes=foo` when the new PM is on (which is true by default).
>
> I imagine this would be a short script that has a list of passes from
> PassRegistry.def and the IR unit they operate on, and looks through RUN
> lines with opt, deleting existing pass arguments and replacing them with a
> -passes= argument. If we have more than one pass, each pass would be
> wrapped in the proper adaptor.  For example, `opt -instcombine -globaldce`
> becomes `opt -passes='function(instcombine),globaldce'`.
>
> We need to make sure that we don't end up causing too many duplicate RUN
> lines if we have tests that specify both `opt -foo` and `opt -passes=foo`.
>
> We should wait until the next LLVM release before changing all opt tests
> since we do want any bots using the legacy PM to still run opt tests
> against the legacy PM. But until then we can pick a couple lesser-used
> passes/test directories to touch up.
>
> Note that this does not include any opt tests that test passes on
> available under the legacy PM, which would be IR passes in the codegen
> pipeline.
>
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