Re: [tree-ssa] Critical edge splitting (was: New regressions as of 2003-11-04)

[Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>]

Hello,

> > Please be aware, that if you guys want, I can also temporarily fix the
> > regression at the cost of possibly redoing dominators + dominance
> > frontiers for every lexical expression we PRE (This is absolute worst
> > case, where every expression has a different set of critical edges we
> > might need to insert on. I don't know how often this happens in
> > practice).
> 
> If critical edge splitting is the whole problem here, why don't you just
> enhance your critical edge splitter to _update_ the relevant information?
> Critical edges only locally change dominance properties, so this is very
> easy.
> 
> If you're interested, the LLVM critical edge splitter updates dominator
> sets, immediate dominators, dominator trees, and dominance frontiers (in
> significantly less than 150 LOC).  The code is here:
> 
> http://llvm.cs.uiuc.edu/doxygen/BreakCriticalEdges_8cpp-source.html
> 
> I'm not sure that I understand what the problem is with presplitting all
> edges, but at least this will give you a nice simple incremental way to do
> it without recalculating the world.  :)

the real problem for me is that things like splitting the edges should
just work.  Yes, recalculating the dominance information is feasible,
but unnecessary, in this particular case.

Zdenek