tree-cfg.c (gimple_seq_unreachable_p): New function.

gcc/
	* tree-cfg.c (gimple_seq_unreachable_p): New function.
	(assert_unreachable_fallthru_edge_p): Use it.
	(group_case_labels_stmt): Likewise.
	* tree-cfg.h: Prototype it.
	* stmt.c: Include cfghooks.h and tree-cfg.h.
	(emit_case_dispatch_table) <gap_label>: New local variable.
	Use it to fill dispatch table gaps.
	Test for default_label before updating probabilities.
	(expand_case) <default_label>: Remove unneeded initialization.
	Test for unreachable default case statement and remove its edge.
	Set default_label accordingly.
	* tree-ssa-ccp.c (optimize_unreachable): Update comment.

gcc/testsuite/
	* gcc.target/powerpc/pr51513.c: New test.
	* gcc.dg/predict-13.c: Replace __builtin_unreachable() with
	__builtin_abort().
	* gcc.dg/predict-14.c: Likewise.

From-SVN: r247844

1 files changed, 31 insertions, 19 deletions

diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
index a540416..77cb3d6 100644
--- a/gcc/tree-cfg.c
+++ b/gcc/tree-cfg.c
@@ -452,6 +452,31 @@ computed_goto_p (gimple *t)
 	  && TREE_CODE (gimple_goto_dest (t)) != LABEL_DECL);
 }
 
+/* Returns true if the sequence of statements STMTS only contains
+   a call to __builtin_unreachable ().  */
+
+bool
+gimple_seq_unreachable_p (gimple_seq stmts)
+{
+  if (stmts == NULL)
+    return false;
+
+  gimple_stmt_iterator gsi = gsi_last (stmts);
+
+  if (!gimple_call_builtin_p (gsi_stmt (gsi), BUILT_IN_UNREACHABLE))
+    return false;
+
+  for (gsi_prev (&gsi); !gsi_end_p (gsi); gsi_prev (&gsi))
+    {
+      gimple *stmt = gsi_stmt (gsi);
+      if (gimple_code (stmt) != GIMPLE_LABEL
+	  && !is_gimple_debug (stmt)
+	  && !gimple_clobber_p (stmt))
+      return false;
+    }
+  return true;
+}
+
 /* Returns true for edge E where e->src ends with a GIMPLE_COND and
    the other edge points to a bb with just __builtin_unreachable ().
    I.e. return true for C->M edge in:
@@ -476,22 +501,7 @@ assert_unreachable_fallthru_edge_p (edge e)
       if (other_bb == e->dest)
 	other_bb = EDGE_SUCC (pred_bb, 1)->dest;
       if (EDGE_COUNT (other_bb->succs) == 0)
-	{
-	  gimple_stmt_iterator gsi = gsi_after_labels (other_bb);
-	  gimple *stmt;
-
-	  if (gsi_end_p (gsi))
-	    return false;
-	  stmt = gsi_stmt (gsi);
-	  while (is_gimple_debug (stmt) || gimple_clobber_p (stmt))
-	    {
-	      gsi_next (&gsi);
-	      if (gsi_end_p (gsi))
-		return false;
-	      stmt = gsi_stmt (gsi);
-	    }
-	  return gimple_call_builtin_p (stmt, BUILT_IN_UNREACHABLE);
-	}
+	return gimple_seq_unreachable_p (bb_seq (other_bb));
     }
   return false;
 }
@@ -1668,9 +1678,11 @@ group_case_labels_stmt (gswitch *stmt)
       gcc_assert (base_case);
       base_bb = label_to_block (CASE_LABEL (base_case));
 
-      /* Discard cases that have the same destination as the
-	 default case.  */
-      if (base_bb == default_bb)
+      /* Discard cases that have the same destination as the default case
+	 or if their destination block is unreachable.  */
+      if (base_bb == default_bb
+	  || (EDGE_COUNT (base_bb->succs) == 0
+	      && gimple_seq_unreachable_p (bb_seq (base_bb))))
 	{
 	  gimple_switch_set_label (stmt, i, NULL_TREE);
 	  i++;