[Bug tree-optimization/39506] PTA TBAA pruning wrong for -fargument-noalias-*

["rguenth at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #7 from rguenth at gcc dot gnu dot org  2009-03-20 10:31 -------
Hm?  In the testcase the argument points to NULL.  I do not see that

 1) assigning sth else to the parameter is forbidden by the optimization switch

 2) we prevent the compiler from coalescing an unrelated SSA_NAME to that
    same base variable decl of the param.

The problem is that may_alias_p get's a pointer DECL, not an SSA_NAME and
checks

  /* If -fargument-noalias-global is > 2, pointer arguments may
     not point to anything else.  */
  if (flag_argument_noalias > 2 && TREE_CODE (ptr) == PARM_DECL)
    {
      alias_stats.alias_noalias++;
      alias_stats.simple_resolved++;
      return false;
    }

which is very fragile.

We can just delete that check entirely and rely on PTA properly tracking if
a pointer still (only) points to the PARM_NOALIAS variable we created for
the points-to set of the incoming pointer SSA_NAME.

Anyway, I won't force a fix down your throat for 4.4 but will just remove
the above code pieces on a-i branch.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39506