[patch] Lno branch merge part 3 -- ssa form updating improvements

[Mark Mitchell]

Mark Mitchell wrote:
>> Well, and to say it bluntly:  we need something *now*, in order to be
>> able to proceed with the rest of the branch merge, and we won't have
>> anything else that would be sufficiently tested soon enough.
> 
> 
> Has it been definitively decided to merge the LNO branch?
> 
> At the Summit, there were some pretty deep reservations expressed about 
> some parts of the LNO branch.  I think that there needs to be some 
> discussion about these issues and probably SC involvement before merging 
> in all of the code.  I think that we should probably be taking advantage 
> of Ken Zadeck's offer to talk about things as well.

I've been informed offline that my words are being subjected to some 
sort of Greenspan-like analysis on IRC.  Are "deep reservations" worse 
than "severe reservations"?  This is truly frightening to me; I'm sure 
poor Alan has to spend days planning for a three-minute press conference...

To be more specific, some people at the summit seemed concerned about 
the scalar evolution code, calling it "too experimental for a production 
compiler."  There seemed to be widespread agreement that the 
replacements for the RTL loop optimizers were a good thing.  Perhaps, 
after further discussion, consensus has been reached that basically the 
entire branch is in good shape.  If so, that's fine by me!

Are there still people who are worried about the code on the LNO branch? 
  If so, would you please articulate your concerns?  Have you looked at 
the LNO branch in enough detail that you feel that you understand what 
it's doing?  Is it possible

I have also been told that the June 30th Stage 2 date is causing 
consternation for the LNO people.  My expectation here is that, while 
the rest of the compiler will enter Stage 2 at that time, it's not 
unreasonable to take some additional LNO functionality in Stage 2, if 
there's clear consensus on the approach, the code has been thoroughly 
tested, etc.  I am trying to balance the desire (articulated by several 
at the summit) that we do releases relatively frequently with the 
equally reasonable desire that we get good optimization technology into 
the compiler as soon as reasonably feasible.

-- 
Mark Mitchell
CodeSourcery, LLC
mark@codesourcery.com