[tree-ssa] Avoid nondeterminism in tree-ssanames

[law@redhat.com]

In message <20031201163306.GW4715@kam.mff.cuni.cz>, Jan Hubicka writes:
 >> Please stop.
 >> 
 >> 1. Re-using SSA_NAMES across different functions is a bad idea.  Please let
 >'s
 >
 >Why?
Because SSA_NAMEs and PHI nodes should be totally removed from the set of
reachable GC nodes once we're done with SSA.  That ought to be an invariant
of the implementation, even if we can't easily verify it.

If SSA_NAMEs or PHI_NODEs are reachable nodes outside the SSA pass, then that
should be considered a bug, either in that we are not zeroing pointer fields
when we should, not removing annotations when we should, etc etc.


 >> So rather than muck around making SSA_NAME (or PHI_NODE) management more
 >> complex, let's instead address the underlying GC issues.
 >
 >OK, how would you propose to fix the problem with non-determinism in
 >short term?
 >This patch was meant as short term fix....
Don't worry about it in the short term.  Instead spend the time dealing with
the GC issues that need to be addressed so that tree-ssanames can go away.

jeff