SSA renaming scheme is dangerous

Bugzilla Link	42
Created on	Aug 04, 2004 17:19
Resolution	FIXED
Resolved on	Aug 05, 2004 23:15
Version	1.00beta
OS	All
Architecture	Sun
Attachments	ssabug.sac

Extended Description

Multiple SSA transformations can lead to multiple declarations of variables due
to SSATransforms renaming scheme.
Take a look at the following example:
int[.], int[.] buggy( int[.] z) 
{
  unew = with (. <= iv <= .) 
         {
           zsum = 2 * z[iv];
         }
         genarray ([1024], zsum);
  unew = with ([0] <= iv <= [0])
         modarray (unew, iv, unew[[1023]]);
  vnew = with (. <= iv <= .)
         {
           zsum = 2 * z[iv];
         }
         genarray ([1024], zsum);
  return (unew, vnew);
}
As the syntaxtree is converted in and out of SSA form during WLEnhancement
(activated via -khf), zsum in the second with-loop is renamed into zsum__SSA1.
After UndoSSATransform in WLEnhancment, zsum__SSA1 is not re-renamed into zsum.
Now, with-loop folding folds the first two with-loops, yielding a new with-loop
with two generators whose results are both names zsum. The subsequent call of
RestoreSSAOneFunction will rename the second result into zsum__SSA1 which
already exists!