[tree-ssa] Loop header copying

[Zdenek Dvorak]

Hello,

> > Index: cfghooks.h
> > ===================================================================
> > RCS file: /cvs/gcc/gcc/gcc/cfghooks.h,v
> > retrieving revision 1.1.2.6
> > diff -c -3 -p -r1.1.2.6 cfghooks.h
> > *** cfghooks.h	3 Nov 2003 17:47:35 -0000	1.1.2.6
> > --- cfghooks.h	8 Dec 2003 20:28:03 -0000
> > *************** struct cfg_hooks
> > *** 51,56 ****
> > --- 51,62 ----
> >     /* Split basic block B after specified instruction I.  */
> >     edge (*split_block) (basic_block b, void * i);
> >   
> > +   /* Split basic block B immediatelly after labels.  */
> > +   edge (*split_block_after_labels) (basic_block b);
> > + 
> > +   /* Move block B immediatelly after block A.  */
> > +   void (*move_block_after) (basic_block b, basic_block a);
> > + 
> 
> I see there is no entry for duplicate_block, but that is just an
> ommision.  Please add it there (either by update of this patch or
> incrementally depending whehter you will need new revision of it).
> This is definitly something we want to hookize.

OK.

> I am not very happy about move_block_after hook.  If it exists, it
> should be somewhat unified with cfglayout way of reordering, but it
> probably ought not be needed at first place.  We shall be completely
> independent on the order of BBS on tree level...

We basically are; however keeping the things in logical order improves
readability of the dumps and decreases the number of jump_insns emitted
during rtl expansion.  I also try to keep the old loop optimizer happy.

> Hmm perhaps it is because you want loops to be lienar regions at RTL
> evel.  This problem seems to be more general as we do create basic
> blocks in arbitrary order now

Where?

> so if we want to be serious about RTL loop
> optimizer we need to reorder blocks during emiting the loop notes, but I
> guess it is moot unless your plans to rewrite cfgloop fails miserably
> (and that would be real disaster so I hope it won't happen). 

Zdenek