[patch] simplifyCFG for review

[Andrew Trick]

On Jul 27, 2013, at 1:30 AM, Chandler Carruth <chandlerc at google.com> wrote:

> 
> On Sat, Jul 27, 2013 at 1:07 AM, Andrew Trick <atrick at apple.com> wrote:
>> (1) In terms of code organization, these anti-canonical, target-selected transforms should live somewhere else. I kept quiet becase I hadn't come up with an alternative, but we can do that now. OptimizeCFG.cpp?
> 
> It would be even more self-evident to group all of these type of branch avoidance utils into a FlattenCFG package. So I'm changing my vote to FlattenCFG.cpp.
> 
> To focus on the immediate issue: I agree.
> 
> Design wise, I would suggest one step further: I think that CFG-flattening of this form is somewhat specialized and we should just build a nice specialized set of optimizations targetting that use case, and have the targets add those passes from their target machine rather than monkey with the general purpose PMB. We can't easily get this right in the PMB because of the silly way CGSCC stuff is defined, and I think that this is likely to be best as a late-stage CFG pass anyways not unlike LSR, etc. I'm not sure that it really has anything to do with SimplifyCFG (or OptimizeCFG, which I've begun to think is somewhat likely to make more sense in MI w/ register pressure and critical path info). So, my vote is for a more targeted tool in the toolbox.

Mei,

You seem to have a reason for running SimplifyParallelAndOr after the basic cleanup transforms but before branch simplification. Whereas MergeIfRegion runs only after all other simplifications. That does seem intuitive to me, but I wonder if it is absolutely necessary. Can you illustrate with an example or two why the simplifications need to be interleaved this way? Are you just trying to avoid the need for another round of iteration in the SimplifyCFGPass driver? I think the direction of design refactoring depends on it.

-Andy
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20130727/a58d7dbe/attachment.html>