if-to-switch: fix matching of negative conditions

gcc/ChangeLog:

	PR tree-optimization/98182
	* gimple-if-to-switch.cc (pass_if_to_switch::execute): Request
	chain linkage through false edges only.

gcc/testsuite/ChangeLog:

	PR tree-optimization/98182
	* gcc.dg/tree-ssa/if-to-switch-10.c: New test.
	* gcc.dg/tree-ssa/pr98182.c: New test.

gcc/gimple-if-to-switch.cc

@@ -522,6 +522,12 @@ pass_if_to_switch::execute (function *fun)
 	      if (!info2 || info->m_ranges[0].exp != info2->m_ranges[0].exp)
 		break;
 
+	      /* It is important that the blocks are linked through FALSE_EDGE.
+		 For an expression of index != VALUE, true and false edges
+		 are flipped.  */
+	      if (info2->m_false_edge != e)
+		break;
+
 	      chain->m_entries.safe_push (info2);
 	      bitmap_set_bit (seen_bbs, e->src->index);
 	      info = info2;

gcc/testsuite/gcc.dg/tree-ssa/if-to-switch-10.c

@@ -0,0 +1,44 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-iftoswitch-optimized" } */
+
+int global;
+int foo ();
+
+int main(int argc, char **argv)
+{
+  if (argc != 1)
+    {
+      if (argc != 2)
+	{
+	  if (argc == 3)
+	    {
+	      foo ();
+	      foo ();
+	    }
+	  else if (argc == 4)
+	    {
+	      foo ();
+	    }
+	  else if (argc == 5)
+	    {
+	      global = 2;
+	    }
+	  else
+	    global -= 123;
+	}
+      else
+	{
+	  global += 1;
+	}
+    }
+  else
+    foo ();
+
+  
+  global -= 12;
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "Canonical GIMPLE case clusters: 1 2 3 4 5" "iftoswitch" } } */
+/* { dg-final { scan-tree-dump "Condition chain with \[^\n\r]\* BBs transformed into a switch statement." "iftoswitch" } } */
+

gcc/testsuite/gcc.dg/tree-ssa/pr98182.c

@@ -0,0 +1,18 @@
+/* PR tree-optimization/98182 */
+/* { dg-do compile } */
+/* { dg-options "-O1 --param case-values-threshold=1 -fdump-tree-iftoswitch-optimized" } */
+
+int global;
+int foo ();
+
+int main(int argc, char **argv)
+{
+  if (argc != 1)
+    __builtin_abort ();
+  else if (argc != 2)
+    __builtin_abort ();
+  else
+    return 0;
+}
+
+/* { dg-final { scan-tree-dump-not "Condition chain" "iftoswitch" } } */