Index: cfe/trunk/lib/Format/TokenAnnotator.cpp
===================================================================
--- cfe/trunk/lib/Format/TokenAnnotator.cpp
+++ cfe/trunk/lib/Format/TokenAnnotator.cpp
@@ -1694,17 +1694,26 @@
   for (SmallVectorImpl<AnnotatedLine *>::reverse_iterator I = Lines.rbegin(),
                                                           E = Lines.rend();
        I != E; ++I) {
-    bool CommentLine = (*I)->First;
+    bool CommentLine = true;
     for (const FormatToken *Tok = (*I)->First; Tok; Tok = Tok->Next) {
       if (!Tok->is(tok::comment)) {
         CommentLine = false;
         break;
       }
     }
-    if (NextNonCommentLine && CommentLine)
-      (*I)->Level = NextNonCommentLine->Level;
-    else
+
+    if (NextNonCommentLine && CommentLine) {
+      // If the comment is currently aligned with the line immediately following
+      // it, that's probably intentional and we should keep it.
+      bool AlignedWithNextLine =
+          NextNonCommentLine->First->NewlinesBefore <= 1 &&
+          NextNonCommentLine->First->OriginalColumn ==
+              (*I)->First->OriginalColumn;
+      if (AlignedWithNextLine)
+        (*I)->Level = NextNonCommentLine->Level;
+    } else {
       NextNonCommentLine = (*I)->First->isNot(tok::r_brace) ? (*I) : nullptr;
+    }
 
     setCommentLineLevels((*I)->Children);
   }
Index: cfe/trunk/unittests/Format/FormatTest.cpp
===================================================================
--- cfe/trunk/unittests/Format/FormatTest.cpp
+++ cfe/trunk/unittests/Format/FormatTest.cpp
@@ -825,12 +825,35 @@
                "  case A:\n"
                "    f();\n"
                "    break;\n"
-               "  // On B:\n"
+               "    // fallthrough\n"
                "  case B:\n"
                "    g();\n"
                "    break;\n"
                "  }\n"
                "});");
+  EXPECT_EQ("DEBUG({\n"
+            "  switch (x) {\n"
+            "  case A:\n"
+            "    f();\n"
+            "    break;\n"
+            "  // On B:\n"
+            "  case B:\n"
+            "    g();\n"
+            "    break;\n"
+            "  }\n"
+            "});",
+            format("DEBUG({\n"
+                   "  switch (x) {\n"
+                   "  case A:\n"
+                   "    f();\n"
+                   "    break;\n"
+                   "  // On B:\n"
+                   "  case B:\n"
+                   "    g();\n"
+                   "    break;\n"
+                   "  }\n"
+                   "});",
+                   getLLVMStyle()));
   verifyFormat("switch (a) {\n"
                "case (b):\n"
                "  return;\n"
Index: cfe/trunk/unittests/Format/FormatTestComments.cpp
===================================================================
--- cfe/trunk/unittests/Format/FormatTestComments.cpp
+++ cfe/trunk/unittests/Format/FormatTestComments.cpp
@@ -805,6 +805,70 @@
             format("namespace {}\n   /* Test */    #define A"));
 }
 
+TEST_F(FormatTestComments, KeepsLevelOfCommentBeforePPDirective) {
+  // Keep the current level if the comment was originally not aligned with
+  // the preprocessor directive.
+  EXPECT_EQ("void f() {\n"
+            "  int i;\n"
+            "  /* comment */\n"
+            "#ifdef A\n"
+            "  int j;\n"
+            "}",
+            format("void f() {\n"
+                   "  int i;\n"
+                   "  /* comment */\n"
+                   "#ifdef A\n"
+                   "  int j;\n"
+                   "}"));
+
+  EXPECT_EQ("void f() {\n"
+            "  int i;\n"
+            "  /* comment */\n"
+            "\n"
+            "#ifdef A\n"
+            "  int j;\n"
+            "}",
+            format("void f() {\n"
+                   "  int i;\n"
+                   "  /* comment */\n"
+                   "\n"
+                   "#ifdef A\n"
+                   "  int j;\n"
+                   "}"));
+
+  // Keep the current level if there is an empty line between the comment and
+  // the preprocessor directive.
+  EXPECT_EQ("void f() {\n"
+            "  int i;\n"
+            "  /* comment */\n"
+            "\n"
+            "#ifdef A\n"
+            "  int j;\n"
+            "}",
+            format("void f() {\n"
+                   "  int i;\n"
+                   "/* comment */\n"
+                   "\n"
+                   "#ifdef A\n"
+                   "  int j;\n"
+                   "}"));
+
+  // Align with the preprocessor directive if the comment was originally aligned
+  // with the preprocessor directive.
+  EXPECT_EQ("void f() {\n"
+            "  int i;\n"
+            "/* comment */\n"
+            "#ifdef A\n"
+            "  int j;\n"
+            "}",
+            format("void f() {\n"
+                   "  int i;\n"
+                   "/* comment */\n"
+                   "#ifdef A\n"
+                   "  int j;\n"
+                   "}"));
+}
+
 TEST_F(FormatTestComments, SplitsLongLinesInComments) {
   EXPECT_EQ("/* This is a long\n"
             " * comment that\n"