Re: [PATCH] make find_taken_edge handle case with just default

[Peter Bergner <bergner at vnet dot ibm dot com>]

On 6/29/17 4:03 AM, Richard Biener wrote:
> 
> This refactors things a bit to make CFG cleanup handle switches with
> just a default label.  If we make sure to cleanup the CFG after
> group_case_labels removes cases with just __builtin_unreachable ()
> inside then this fixes the ICE seen in PR81994 as well.
> 
> I wonder if find_taken_edge should generally handle successors
> with __builtin_unreachable () -- OTOH that would get rid of those
> too early I guess.

Should we offer an early out of group_case_labels_stmt() for the
fairly common case of new_size == old_size?  There's no reason to
execute the compress labels loop if we didn't combine any of the
labels.

Peter


Index: gcc/tree-cfg.c
===================================================================
--- gcc/tree-cfg.c	(revision 249783)
+++ gcc/tree-cfg.c	(working copy)
@@ -1747,6 +1747,11 @@ group_case_labels_stmt (gswitch *stmt)
 	}
     }

+  gcc_assert (new_size <= old_size);
+
+  if (new_size == old_size)
+    return false;
+
   /* Compress the case labels in the label vector, and adjust the
      length of the vector.  */
   for (i = 0, j = 0; i < new_size; i++)
@@ -1757,9 +1762,8 @@ group_case_labels_stmt (gswitch *stmt)
 			       gimple_switch_label (stmt, j++));
     }

-  gcc_assert (new_size <= old_size);
   gimple_switch_set_num_labels (stmt, new_size);
-  return new_size < old_size;
+  return true;
 }

 /* Look for blocks ending in a multiway branch (a GIMPLE_SWITCH),