[Bug fortran/42131] Weird translation of DO loops

[rguenther at suse dot de]

------- Comment #21 from rguenther at suse dot de  2009-11-30 10:10 -------
Subject: Re:  Weird translation of DO loops

On Mon, 30 Nov 2009, tkoenig at gcc dot gnu dot org wrote:

> ------- Comment #20 from tkoenig at gcc dot gnu dot org  2009-11-30 07:31 -------
> Created an attachment (id=19182)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19182&action=view)
>  --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19182&action=view)
> Patch that works for unrolling
> 
> It also passes do_3.F90.
> 
> I'll submit just in time for meeting the phase 4 deadline tonight (hopefully).

If it works for unrolling it must be indeed better.  Though:

+      /* Calculate SIGN (1,step) */
+
+      tmp = fold_build2 (RSHIFT_EXPR, type, step,
+                        build_int_cst (type,
+                                       TYPE_PRECISION (type) - 1));
+
+      tmp = fold_build2 (MULT_EXPR, type, tmp,
+                        build_int_cst (type, 2));
+
+      step_sign = fold_build2 (PLUS_EXPR, type, tmp,
+                              fold_convert (type, integer_one_node));

the "sign" for unsigned steps is always 1, you don't seem to account
for unsignedness?  Note that I believe generating

  step_sign = fold_build3 (fold_build2 (LT_EXPR, boolean_type_node,
                                  step, build_int_cst (TREE_TYPE (step), 
0)),
                     build_int_cst (type, -1), build_int_cst (type, 1));

is better as that allows more freedom for fold and efficient expansion
for the target.  Just double-check that it also works for the
unrolling ;)

Thanks,
Richard.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42131