[llvm-dev] Renaming passes

[Fangrui Song via llvm-dev]

On 2020-06-24, Arthur Eubanks via llvm-dev wrote:
>On Wed, Jun 24, 2020 at 4:48 PM Matt Arsenault <arsenm2 at gmail.com> wrote:
>
>>
>>
>> On Jun 24, 2020, at 19:17, Arthur Eubanks <aeubanks at google.com> wrote:
>>
>>
>>
>> On Wed, Jun 24, 2020 at 12:23 PM Philip Reames <listmail at philipreames.com>
>> wrote:
>>
>>>
>>> On 6/24/20 11:21 AM, Matt Arsenault via llvm-dev wrote:
>>>
>>>
>>>
>>> On Jun 24, 2020, at 14:13, Arthur Eubanks via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>> Hi,
>>>
>>> As part of new pass manager work, I've been trying to get something like
>>> `opt -foo` working under the NPM, where `foo` is the name of a pass.
>>>
>>> In the past there's been no reason to keep the names of passes consistent
>>> between NPM and legacy PM. But now there is a reason to make them match, so
>>> that we don't have to touch every single test that uses `opt`.
>>>
>>> There are a couple of names that don't match though, for example the
>>> "basic alias analysis" pass is named "basicaa" under the legacy PM
>>> INITIALIZE_PASS_BEGIN(BasicAAWrapperPass, "basicaa",
>>>                       "Basic Alias Analysis (stateless AA impl)", true,
>>> true)
>>> but named "basic-aa" under the NPM
>>> FUNCTION_ALIAS_ANALYSIS("basic-aa", BasicAA())
>>> . Almost all the other AA passes have a dash in them so I think it makes
>>> sense to rename "basicaa" -> "basic-aa".
>>>
>>> Is there accepted wisdom on renaming pass names? Is a pass name a stable
>>> interface? When is it ok to rename a pass? If there are 800 usages of a
>>> flag, should I rename them atomically?
>>>
>>>
>>> I think the pass naming scheme needs a lot of work. The naming
>>> conventions seem random at times. For instance, I can never remember how to
>>> refer to PrologEpilogInserter. The DEBUG_TYPE name is “prologepilog”, the
>>> pass class name is “PEI”. I would expect this to be prolog-epilog-inserter
>>> to match the file and formal pass name, and consistently use dashes as word
>>> separators.
>>>
>>> Can I suggest we allow aliases?  We can except all of these names, pick a
>>> canonical name, migrate tests, and only remove the aliases once the new
>>> canonical names are widely known.
>>>
>> An alias sounds good.
>>
>>
>> In what contexts? I think aliases for the handful of potentially end user
>> facing cases may be acceptable, but would worry about adding aliases
>> everywhere. I think renaming things directly referring to a pass can be
>> done pretty easily with a simple script?
>>
>My plan was to add an alias in PassNameParser, switch over all references
>to use the new one, then remove the alias. In order to avoid one change
>that touches 800 files. Also any rollbacks are easier.

An alias facility in PassNameParser sounds good. Dropping the alias can
be a separate change so that rollback will be easier.