[LLVMdev] Would like to force one minor, mechanical change on out-of-tree users of the old pass manager

[David Blaikie]

On Wed, Jan 28, 2015 at 12:56 PM, Chandler Carruth <chandlerc at gmail.com>
wrote:

> Greetings folks.
>
> I had really wanted out-of-tree folks to be able to make only a single
> change to their code due to the new pass manager; essentially, by the time
> they had to touch the code at all I wanted them to be able to port
> completely to the new pass manager.
>
> However, Richard has raised the issue that this is nearly impossible to
> make work with C++ modules, and we've lost the modules build bot that was
> checking our self host in this mode because of this.
>

What was the change in particular that broke modules?

I'm not quite understanding the setup we've ended up with that causes this
problem - why is it that the new pass manager doesn't use a temporary
name/namespace until it finishes, leaving the original in place?


> So, now that 3.6 is branched, I wondered if folks would be OK with me
> switching code to explicitly refer to some of the legacy constructs with
> the "legacy" namespace. I'm absolutely committed to the new pass manager
> being done prior to 3.7 (actually, a lot sooner). So this would require
> (entirely mechanical) source changes to out-of-tree users who are tracking
> trunk in the interim.
>
> However, the changes would only be required for Pass*Manager* and related
> classes. Neither Pass, FunctionPass, or PassManagerBuilder would change.
>
> Any objections to this? While it clearly has cost and would not be my
> preferred approach, the benefits seem to outweigh the costs here.
>
> -Chandler
>
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