[tree-ssa] Lazy updating of stmt operands

[law@redhat.com]

In message <Pine.LNX.4.44.0312111514190.2582-100000@nondot.org>, Chris Lattner 
writes:
 >
 >Jeff Law wrote:
 >
 >> While it's nice to think about a world where you always have immediate
 >> uses, you end up with FUD chains if you do that -- with ultimately a
 >> tangled nest of pointers that is bloody impossible to work with in the
 >> real world.
 >
 >Uh, no.  Here's a counter-example:
 >http://llvm.cs.uiuc.edu/
 >
 >Having efficient, transparently & efficiently updated immediate use
 >information is extremely valuable for a wide variety of optimizations.
OK.  Maybe it was just Diego implementation that was an unmaintainable
mess :-)

jeff