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

[Philip Reames via llvm-dev]

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 
> <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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