Fix clustering algorithm in switch expansion.

2018-06-28  Martin Liska  <mliska@suse.cz>

	* tree-switch-conversion.c (jump_table_cluster::find_jump_tables):
        Add new checking assert to catch invalid state.
	(jump_table_cluster::can_be_handled): Handle single case
        clusters.
	(jump_table_cluster::is_beneficial): Bail out for such case.
	(bit_test_cluster::find_bit_tests):
        Add new checking assert to catch invalid state.
	(bit_test_cluster::can_be_handled): Handle single case
        clusters.
	(bit_test_cluster::is_beneficial): Bail out for such case.
	(switch_decision_tree::analyze_switch_statement):
        Fix comment.
2018-06-28  Martin Liska  <mliska@suse.cz>

	* gcc.dg/tree-ssa/switch-1.c: New test.

From-SVN: r262211

1 files changed, 25 insertions, 2 deletions

diff --git a/gcc/tree-switch-conversion.c b/gcc/tree-switch-conversion.c
index 029ce8c..ddd8cba 100644
--- a/gcc/tree-switch-conversion.c
+++ b/gcc/tree-switch-conversion.c
@@ -1121,6 +1121,8 @@ jump_table_cluster::find_jump_tables (vec<cluster *> &clusters)
 	      && can_be_handled (clusters, j, i - 1))
 	    min[i] = min_cluster_item (min[j].m_count + 1, j, s);
 	}
+
+      gcc_checking_assert (min[i].m_count != INT_MAX);
     }
 
   /* No result.  */
@@ -1172,8 +1174,13 @@ jump_table_cluster::can_be_handled (const vec<cluster *> &clusters,
   if (!flag_jump_tables)
     return false;
 
-  unsigned HOST_WIDE_INT max_ratio = optimize_insn_for_size_p () ? 3 : 8;
+  /* For algorithm correctness, jump table for a single case must return
+     true.  We bail out in is_beneficial if it's called just for
+     a single case.  */
+  if (start == end)
+    return true;
 
+  unsigned HOST_WIDE_INT max_ratio = optimize_insn_for_size_p () ? 3 : 8;
   unsigned HOST_WIDE_INT range = get_range (clusters[start]->get_low (),
 					    clusters[end]->get_high ());
   /* Check overflow.  */
@@ -1197,6 +1204,10 @@ bool
 jump_table_cluster::is_beneficial (const vec<cluster *> &,
 				   unsigned start, unsigned end)
 {
+  /* Single case bail out.  */
+  if (start == end)
+    return false;
+
   return end - start + 1 >= case_values_threshold ();
 }
 
@@ -1226,6 +1237,8 @@ bit_test_cluster::find_bit_tests (vec<cluster *> &clusters)
 	      && can_be_handled (clusters, j, i - 1))
 	    min[i] = min_cluster_item (min[j].m_count + 1, j, INT_MAX);
 	}
+
+      gcc_checking_assert (min[i].m_count != INT_MAX);
     }
 
   /* No result.  */
@@ -1277,6 +1290,12 @@ bool
 bit_test_cluster::can_be_handled (const vec<cluster *> &clusters,
 				  unsigned start, unsigned end)
 {
+  /* For algorithm correctness, bit test for a single case must return
+     true.  We bail out in is_beneficial if it's called just for
+     a single case.  */
+  if (start == end)
+    return true;
+
   unsigned HOST_WIDE_INT range = get_range (clusters[start]->get_low (),
 					    clusters[end]->get_high ());
   auto_bitmap dest_bbs;
@@ -1308,6 +1327,10 @@ bool
 bit_test_cluster::is_beneficial (const vec<cluster *> &clusters,
 				 unsigned start, unsigned end)
 {
+  /* Single case bail out.  */
+  if (start == end)
+    return false;
+
   auto_bitmap dest_bbs;
 
   for (unsigned i = start; i <= end; i++)
@@ -1599,7 +1622,7 @@ switch_decision_tree::analyze_switch_statement ()
   /* Find jump table clusters.  */
   vec<cluster *> output = jump_table_cluster::find_jump_tables (clusters);
 
-  /* Find jump table clusters.  */
+  /* Find bit test clusters.  */
   vec<cluster *> output2;
   auto_vec<cluster *> tmp;
   output2.create (1);