[llvm] r209386 - Override runOnMachineFunction for ARMISelDAGToDAG so that we can

[Eric Christopher]

On Thu, May 22, 2014 at 12:46 PM, Bob Wilson <bob.wilson at apple.com> wrote:
>
> On May 22, 2014, at 11:29 AM, Tim Northover <t.p.northover at gmail.com> wrote:
>
>>> Preparation for something bigger, basically the CGContext stuff from
>>> another thread. The basic idea comes down to being able to link
>>> together modules (or include in a single module) functions which
>>> target different subtargets/subtarget features and still be able to
>>> codegen and optimize them correctly. It's similar to some of the
>>> function specific optimization that happened recently.
>>
>> Oh, excellent! Looking forward to seeing more of that.
>
> I’m concerned that this is the wrong approach. Especially as we start thinking about parallel compilation, I really think we need to be explicit about the context. We ought to be moving toward having runOnMachineFunction take a CGContext as an argument, with all the target information and other context accessible via the CGContext.  This patch seems to be further entrenching the current approach of having a single global target that is specified implicitly, not explicitly.
>
> If I’ve missed some discussions that explain how this fits into the bigger picture of what we need to do, can you point me at it? If those discussions haven’t happen yet, this would be a good time to start.

This happened in the CGContext thread.

And yes, I agree, however, unless you want parallel pass managers then
you'll _still_ need to do this. Also you still don't want to globally
set what's legal based on a single target machine.

This is all scaffolding to make this work and is incremental.

-eric