rle.sac failure: LACSO vs. DCR causes crash in WLIR

Bugzilla Link	1034
Created on	Nov 08, 2012 23:05
Version	svn
OS	Linux
Architecture	PC
Attachments	crud.breaks.sac

Extended Description

cd sac/apex/rle
sac@rattler:~/sac/apex/rle$ sac2c rle.sac -v1 
stdopt/withloop_invariant_removal.c:861 Assertion "AVIS_DEFDEPTH(ID_AVIS(arg_node)) != DD_UNDEFINED" failed!
reference to undefined identifier _lacso_17413
sac@rattler:~/sac/apex/rle$ sac2c rle.sac -v1 -nolacso 
sac2c -V
sac@rattler:~/sac/apex/rle$ sac2c -V
sac2c v1.00-beta (Haggis And Apple)
 developer rev 18019 linux-gnu_x86_64
 (Thu Nov  8 17:08:16 EST 2012 by sac)
I believe what is going on is this:
1. LACSO introduces a new scalar result value, which
   is never used in the calling context, but it IS used
   as an AVIS_SHAPE element in the called context.
2. DCR comes along, sees that the result value is unused in
   the caller, so deletes the N_funcond after the recursive
   call, which then marks the recursive call result dead.
3. Things eventually die in WLIR.
I think the correct fix is to make DCR check for 
uses of the result value in AVIS son nodes, and mark
the avis as live if that is the case. I don't like this
approach, but have no better ideas yet.