llvm dev - Jul 2020 - [RFC] Introducing classes for the codegen driven by new pass manager

> On Jul 15, 2020, at 09:16, Robinson, Paul via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
>> I'd just note that not every pass you can run with "opt"
is actually part of the optimization pipeline. There are a few important
IR-level passes that only run in the codegen pipeline, but are still nameable
with opt to run individually for testing purposes. Switching over doesn't
need to block on these passes being migrated. So I'm not sure this method of
determining progress towards switching to NPM actually makes sense.
> 
> FTR, there are IR-level passes that only run in the codegen pipeline,
> and are *not* available in opt, but are available in llc; for example 
> the stack protector pass.  Just throwing that out there.
> --paulr
I would consider these to be bugs. These passes tend to be poorly tested and
don’t have nice single pass tests

-Matt

In codegen with NPM, I've made all codegen passes (IR or MIR pass) to be
only driven by `llc`. Both due to the way NPM registering pass
(on-demand&dynamic instead of static initialization in Legacy PM), and
reduce the confusion about which tool (`llc` or `opt`) to test codegen IR
passes.

________________________________________
From: llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Matt
Arsenault via llvm-dev <llvm-dev at lists.llvm.org>
Sent: Wednesday, July 15, 2020 6:57 AM
To: Robinson, Paul
Cc: llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] [RFC] Introducing classes for the codegen driven by new
pass manager


> On Jul 15, 2020, at 09:16, Robinson, Paul via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
>
>> I'd just note that not every pass you can run with "opt"
is actually part of the optimization pipeline. There are a few important
IR-level passes that only run in the codegen pipeline, but are still nameable
with opt to run individually for testing purposes. Switching over doesn't
need to block on these passes being migrated. So I'm not sure this method of
determining progress towards switching to NPM actually makes sense.
>
> FTR, there are IR-level passes that only run in the codegen pipeline,
> and are *not* available in opt, but are available in llc; for example
> the stack protector pass.  Just throwing that out there.
> --paulr
I would consider these to be bugs. These passes tend to be poorly tested and
don’t have nice single pass tests

-Matt
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> On Jul 15, 2020, at 12:28, Chen, Yuanfang <Yuanfang.Chen at sony.com>
wrote:
> 
> In codegen with NPM, I've made all codegen passes (IR or MIR pass) to
be only driven by `llc`. Both due to the way NPM registering pass
(on-demand&dynamic instead of static initialization in Legacy PM), and
reduce the confusion about which tool (`llc` or `opt`) to test codegen IR
passes.
> 

I think there’s no real distinction between “codegen” IR passes and noncodegen
IR passes. I routinely run “codegen only” passes with opt in conjunction with
other passes when experimenting. I think losing the ability to run any IR pass
with opt would be a functionality regression.

-Matt