[committed] Fix -Wimplicit-fallthrough with [[{,un}likely]] attributes on labels (PR c++/91024)

[Jakub Jelinek]

Hi!

The likely/unlikely C++11 attributes on case labels result in GIMPLE_PREDICT
statements inserted after the label; we should just ignore such statements,
they aren't something executable in between the labels.

Bootstrapped/regtested on x86_64-linux and i686-linux, committed to trunk,
queued for backporting to 9.2.

2019-06-27  Jakub Jelinek  <jakub@redhat.com>

	PR c++/91024
	* gimplify.c (collect_fallthrough_labels): Ignore GIMPLE_PREDICT
	statements.

	* g++.dg/warn/Wimplicit-fallthrough-4.C: New test.

--- gcc/gimplify.c.jj	2019-06-15 09:08:03.383953216 +0200
+++ gcc/gimplify.c	2019-06-27 20:03:31.943295216 +0200
@@ -2120,6 +2120,8 @@ collect_fallthrough_labels (gimple_stmt_
 	}
       else if (gimple_call_internal_p (gsi_stmt (*gsi_p), IFN_ASAN_MARK))
 	;
+      else if (gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_PREDICT)
+	;
       else if (!is_gimple_debug (gsi_stmt (*gsi_p)))
 	prev = gsi_stmt (*gsi_p);
       gsi_next (gsi_p);
--- gcc/testsuite/g++.dg/warn/Wimplicit-fallthrough-4.C.jj	2019-06-27 20:13:08.557572047 +0200
+++ gcc/testsuite/g++.dg/warn/Wimplicit-fallthrough-4.C	2019-06-27 20:14:12.399606229 +0200
@@ -0,0 +1,22 @@
+// PR c++/91024
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wimplicit-fallthrough" }
+
+int
+foo (char c)
+{
+  int result = 0;
+
+  switch (c)
+    {
+    case 'O':
+    case 'K':
+      return result;
+    [[unlikely]] case 'X':	// { dg-bogus "this statement may fall through" }
+    case 'x':			// { dg-bogus "here" }
+      return result;
+    default:
+      break;
+    }
+  return result;
+}

	Jakub