[ast-optimizer-branch]: Fix for incorrect scope building

[Daniel Berlin <dberlin at dberlin dot org>]

For 
if (a)
win:
return 1;

we build

if (a)
{
	win:;
}
and lose the return 1.

This causes things like infinite loops in reg_class_subset_p, which jumps 
to win when it finds something (and thus, falls back through, rather than 
returning 1).


The problem is that when building the scope, we chain the end scope to *t, 
replacing whatever it was chained to already, rather than chain it to the 
last thing in the chain of *t.

This only probably hits LABEL_STMTS, where for the purposes of turning 
something without a compound statement, into something with one, we need 
to ignore the label_stmt, since it's not counted.

So if we convert non-compounds into compounds anywhere else, we need to 
watch this.

Index: c-simplify.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/Attic/c-simplify.c,v
retrieving revision 1.1.2.15
diff -c -3 -p -w -B -b -r1.1.2.15 c-simplify.c
*** c-simplify.c        2 May 2002 19:42:00 -0000       1.1.2.15
--- c-simplify.c        4 May 2002 19:43:52 -0000
*************** tree_build_scope (t)
*** 1902,1908 ****
      {
        /* Construct a compound statement and a scope.  */
        tree body, start_scope, end_scope;
!
        body = make_node (COMPOUND_STMT);
        start_scope = make_node (SCOPE_STMT);
        end_scope = make_node (SCOPE_STMT);
--- 2033,2039 ----
      {
        /* Construct a compound statement and a scope.  */
        tree body, start_scope, end_scope;
!       tree endplace;
        body = make_node (COMPOUND_STMT);
        start_scope = make_node (SCOPE_STMT);
        end_scope = make_node (SCOPE_STMT);
*************** tree_build_scope (t)
*** 1910,1916 ****
        SCOPE_BEGIN_P (end_scope) = 0;
        COMPOUND_BODY (body) = start_scope;
        TREE_CHAIN (start_scope) = *t;
!       TREE_CHAIN (*t) = end_scope;
        *t = body;
      }
  }
--- 2041,2050 ----
        SCOPE_BEGIN_P (end_scope) = 0;
        COMPOUND_BODY (body) = start_scope;
        TREE_CHAIN (start_scope) = *t;
!       endplace = *t;
!       while (TREE_CHAIN (endplace))
!         endplace = TREE_CHAIN (endplace);
!       TREE_CHAIN (endplace) = end_scope;
        *t = body;
      }
  }