PRE lossage

[Andrew MacLeod]

On Tue, 2003-10-28 at 14:25, Daniel Berlin wrote:
> 
> On Oct 28, 2003, at 2:17 PM, law@redhat.com wrote:
> 
> > In message <64E3BF94-097A-11D8-A9DD-000A95AF1FAE@dberlin.org>, Daniel 
> > Berlin wr
> > ites:
> >> I've been putting off these bugs until switch lowering happens, since
> >> that should allow us to pre-split the critical edges without any
> >> trouble, and once that happens, insertion shouldn't require creating
> >> new blocks, ever, and the whole problem goes away.
> > I would be very wary of pre-splitting critical edges.  In my 
> > experience, it
> > loses, badly.
> 
> Except that every compiler i know of does it (LLVM does it, Open64 does 
> it, Intel's compiler does it, etc), and the papers for SSAPRE assume it 
> specifically.
> We also have to recompute a whole bunch of info if we split a critical 
> edge (dominators, dominance frontiers, etc), and can't run ESSA 
> minimization.

It doesnt really change that information very much does it?  It should
be easily updatable when the split happens...  (dominator, etc by the
splitting routine)

Andrew