Re: [vta, graphite?] propagate degenerate phi nodes into debug stmts

[Richard Guenther <richard.guenther@gmail.com>]

On Sun, Nov 8, 2009 at 8:46 AM, Alexandre Oliva <aoliva@redhat.com> wrote:
> This patch arranges for PHI nodes to be propagated into debug stmts upon
> release, if possible.  This improves debug info quality a bit, for
> without this change we'd end up resetting the debug stmt.
>
> It's not clear to me how this helped (if at all) graphite failures with
> VTA, but it helped retain debug annotations that enabled me to validate
> the fix for PR 41926 in a C testcase.  But that's something for another
> patch.
>
> Bootstrapped on x86_64-linux-gnu; regstrapping on that and
> ia64-linux-gnu.  Ok to install?

@@ -383,13 +402,22 @@ insert_debug_temp_for_var_def (gimple_st
             dead SSA NAMEs.  SSA verification shall catch any
             errors.  */
          if ((!gsi && !gimple_bb (def_stmt))
-             || !walk_gimple_op (def_stmt, find_released_ssa_name,
-                                 &wi))
+             || walk_gimple_op (def_stmt, find_released_ssa_name, &wi))
            no_value = true;

please install this as a separate revision - it seems to be an unrelated bugfix.

For the rest it would be better to re-organize the code as

-  if (is_gimple_assign (def_stmt))
     {
... keep unchanged ...
     }
   else if (gimple_code (def_stmt) == PHI_NODE)
     {
        value = degenerate_phi_result (def_stmt);
        if (value
            && walk_tree (&value, find_released_ssa_name, NULL, NULL))
          value = NULL_TREE;
     }

that looks simpler and it avoids walking PHI args uselessly.

@@ -479,6 +508,13 @@ insert_debug_temps_for_defs (gimple_stmt

   stmt = gsi_stmt (*gsi);

+  if (gimple_code (stmt) == GIMPLE_PHI)
+    {
+      tree var = gimple_phi_result (stmt);
+      insert_debug_temp_for_var_def (gsi, var);
+      return;
+    }
+

This looks odd.  SSA DEF operand iteration should walk the PHI defs
as well, so the change should not be necessary.

Ok with that changes.

Thanks,
Richard.

>
>
> --
> Alexandre Oliva, freedom fighter    http://FSFLA.org/~lxoliva/
> You must be the change you wish to see in the world. -- Gandhi
> Be Free! -- http://FSFLA.org/   FSF Latin America board member
> Free Software Evangelist      Red Hat Brazil Compiler Engineer
>
>