proposal for compilation unil wide alias analyis

[Jan Hubicka]

> Jan Hubicka wrote:
> 
> >>Agreed on both points -- both that it can be effective, and that we need 
> >>to demonstrate that it works with GCC.  I think we want to avoid 
> >>committing to (say) making the tree->rtl expanders accept only SSA-form 
> >>GIMPLE until we can demonstrate that it will be a compile-time win to do 
> >>so.
> >>   
> >>
> >
> >Only experiment in this direction I made so far was to build CFG at -O0
> >unconditionally and do tree cleanup_cfg before expanding (this was
> >needed for the CFG transparent RTL expansion task).  The results were
> >about 4% speedup on combine.c compilation times. The speedup ranged from
> >noise to 8% on real world testcases I tested even tought the tree
> >cleanup_cfg is surprisingly expensive (ie doing 7 RTL cleanups accounts
> >together 1/4th of time of the single tree cleanup, any idea why?)
> > 
> >
> If the results were that good, is there any reason not to check in this 
> change?  Perhaps you could post it and get people to evaluate it on some 
> other code.  If we're seeing those kinds of improvements, we definitely 
> want it!

It is checked in already ;) (so we basically go into low gimple and
trees always)

Honza
> 
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> Mark Mitchell
> CodeSourcery, LLC
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>