val_lt_val guard causes AWLF failure

Bugzilla Link	989
Created on	Jul 06, 2012 18:54
Version	svn
OS	Linux
Architecture	PC

Extended Description

This is a day-0 problem with guards, affecting those guards having
two arguments. As an example, this AWLF unit test:
use Array: {iota,sum};
int[*] id(int[*] y)
{
 return(y);
}
int main()
{
  N = _max_SxS_( 1, id(20));
  ZZ = with { ([1] <= iv=[i] <= .)
          { temp = iota( i); 
            offset = _sub_SxS_( i, 1);
            el = _sel_VxA_( [offset], temp);
          } : el;
        } : genarray( [ N], 42);
  ZZZ = sum(ZZ);
  z = _sub_SxS_(ZZZ, 213);
  return(z);
}
If compiled with:
sac2c ~/sac/testsuite/optimizations/awlf/selInWL.sac -doawlf -nowlf -bopt:uglf
this fails to AWLF the iota() out of existence, because we have, essentially:
  offset = i - 1;
  p, offset' = val_lt_val( offset, i);
This can not be rewritten a la CTZ, because the guard result must be
PRF_ARG1, so we must not tinker with offset.
We can, however, rewrite it as:
   p = offset < i;
   offset' = guard( offset, all(p));
I'll put it on my list to write a traversal for this, unless someone
is keen to do it first.