Re: [RFC] WHOPR - A whole program optimizer framework for GCC

["Ollie Wild" <aaw at google dot com>]

On Dec 12, 2007 11:14 PM, Praveen Raghavan <praveen.gcc@gmail.com> wrote:
>
> 1. Are there also plans to extend the global transformation
> capabilities. I see that the original set of global transformations is
> limited (rightfully so).

This is still at a very early design stage.  Additional
transformations could (and should) be added where they make sense.
The main constraints to consider are the time and memory requirements
of the WPA phase.  Since this is the only phase which can't be
parallelized, its scalability is paramount.

> 2. Also any thoughts on how you keep the complete GIMPLE
> representation of millions of functions together? You would have some
> serious complexity issues inside the WPA engine?
> Or is it the idea that you start with the minimal information in the
> wpo1 file and if required read in the GIMPLE section?

You don't.  WPA is the only global phase, and it operates only on
summary data.  The actually reading of GIMPLE occurs in LTRANS, which
partitions the problem.  Depending on how large partitions need to be
before reasonable performance benefits are observed, it may be
necessary to allow LTRANS to swap functions in and out of memory.
That's still an open question.

> 3. Is there a plan/schedule on when 'a' version of this would be out?

TBD.

Ollie