diff mbox

[PR68715] Add missing single_pred_p test in scop_detection::merge_sese

Message ID 56E9327B.9040108@mentor.com
State New
Headers show

Commit Message

Tom de Vries March 16, 2016, 10:16 a.m. UTC 
On 16/03/16 09:53, Richard Biener wrote:
> Hmm, it looks like for all what this function does this effectively
> pessimizes scop merging and it would be easier to split 'exit'
> in case its destination is unsuitable (not trivially empty).
>

Agreed.

> The
>
>    /* For now we just want to bail out when exit does not post-dominate
> entry.
>       TODO: We might just add a basic_block at the exit to make exit
>       post-dominate entry (the entire region).  */
>    if (!dominated_by_p (CDI_POST_DOMINATORS, get_entry_bb (combined),
>                         get_exit_bb (combined))
>        || !dominated_by_p (CDI_DOMINATORS, get_exit_bb (combined),
>
> comment also suggests that splitting the get_nearest_pdom_with_single_exit
> edge and including the new BB in the combined region would also always fix
> the dominance relation (though I don't see how it could do that and
> the comment looks wrong and by construction the check should never
> trigger).
>

I've replaced the entire condition with two asserts:
...
    /* FIXME: We should remove this piece of code once
       canonicalize_loop_closed_ssa has been removed, because that function
...
and ran graphite.exp.

I ran into an ICE for pr68693.f90, for the second assert. The exit bb 
has two incoming edges from within the sese, and one from outside. Given 
that the exit bb is empty, we could split the exit edge and redirect the 
edge from outside the sese to the new bb, which would fix the sese.

Perhaps that is what is meant in the comment, I'm not sure.

Thanks,
- Tom
diff mbox

Patch

diff --git {a,b}/gcc/graphite-scop-detection.c
index 7615842..762a248 100644
--- a/gcc/graphite-scop-detection.c
+++ b/gcc/graphite-scop-detection.c
@@ -820,14 +820,10 @@  scop_detection::merge_sese
    /* For now we just want to bail out when exit does not post-dominate
       entry.
       TODO: We might just add a basic_block at the exit to make exit
       post-dominate entry (the entire region).  */
-  if (!dominated_by_p (CDI_POST_DOMINATORS, get_entry_bb (combined),
-                      get_exit_bb (combined))
-      || !dominated_by_p (CDI_DOMINATORS, get_exit_bb (combined),
-                         get_entry_bb (combined)))
-    {
-      DEBUG_PRINT (dp << "[scop-detection-fail] cannot merge "
-                   "seses.\n");
-      return invalid_sese;
-    }
+  gcc_assert (dominated_by_p (CDI_POST_DOMINATORS,
+                              get_entry_bb (combined),
+                              get_exit_bb (combined)));
+  gcc_assert (dominated_by_p (CDI_DOMINATORS,
+                              get_exit_bb (combined),
+                              get_entry_bb (combined)));