mode-switching: Tweak entry/exit handling

An entity isn't transparent in a block that requires a specific mode.
optimize_mode_switching took that into account for normal insns,
but didn't for the exit block.  Later patches misbehaved because
of this.

In contrast, an entity was correctly marked as non-transparent
in the entry block, but the reasoning seemed a bit convoluted.
It also referred to a function that no longer exists.
Since KILL = ~TRANSP, the entity is by definition not transparent
in a block that defines the entity, so I think we can make it so
without comment.

Finally, the exit handling was nested in the entry handling,
but that doesn't seem necessary.  A target could say that an
entity is undefined on entry but must be defined on return,
on a "be liberal in what you accept, be conservative in what
you do" principle.

gcc/
	* mode-switching.cc (optimize_mode_switching): Mark the exit
	block as nontransparent if it requires a specific mode.
	Handle the entry and exit mode as sibling rather than nested
	concepts.  Remove outdated comment.

diff --git a/gcc/mode-switching.cc b/gcc/mode-switching.cc
index 03dd4c1ebe4060fd6c2667a0eb1181612126c21c..1145350ca26f860dbc705453881d5d2c312cd17e 100644 (file)
--- a/gcc/mode-switching.cc
+++ b/gcc/mode-switching.cc
@@ -650,34 +650,30 @@ optimize_mode_switching (void)
        }
       if (targetm.mode_switching.entry && targetm.mode_switching.exit)
        {
-         int mode = targetm.mode_switching.entry (e);
-
          info[post_entry->index].mode_out =
            info[post_entry->index].mode_in = no_mode;
-         if (pre_exit)
-           {
-             info[pre_exit->index].mode_out =
-               info[pre_exit->index].mode_in = no_mode;
-           }
 
+         int mode = targetm.mode_switching.entry (e);
          if (mode != no_mode)
            {
-             bb = post_entry;
-
-             /* By always making this nontransparent, we save
-                an extra check in make_preds_opaque.  We also
-                need this to avoid confusing pre_edge_lcm when
-                antic is cleared but transp and comp are set.  */
-             bitmap_clear_bit (transp_all, bb->index);
-
              /* Insert a fake computing definition of MODE into entry
                 blocks which compute no mode. This represents the mode on
                 entry.  */
-             info[bb->index].computing = mode;
+             info[post_entry->index].computing = mode;
+             bitmap_clear_bit (transp_all, post_entry->index);
+           }
 
-             if (pre_exit)
-               info[pre_exit->index].seginfo->mode =
-                 targetm.mode_switching.exit (e);
+         if (pre_exit)
+           {
+             info[pre_exit->index].mode_out =
+               info[pre_exit->index].mode_in = no_mode;
+
+             int mode = targetm.mode_switching.exit (e);
+             if (mode != no_mode)
+               {
+                 info[pre_exit->index].seginfo->mode = mode;
+                 bitmap_clear_bit (transp_all, pre_exit->index);
+               }
            }
        }