From 41de040ecfb151f37c7825d0cb0875e950fc9565 Mon Sep 17 00:00:00 2001
From: Cameron McCormack <cam@mcc.id.au>
Date: Sat, 1 Jun 2019 08:03:42 +0000
Subject: [PATCH] Bug 1553731 - Part 3: Make nsIFrame::Is___Frame() avoid
 reading from memory. r=mats

Differential Revision: https://phabricator.services.mozilla.com/D32605

--HG--
extra : moz-landing-system : lando
---
 layout/generic/GenerateFrameLists.py |  2 +-
 layout/generic/nsIFrame.h            | 18 ++++++++++++++----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/layout/generic/GenerateFrameLists.py b/layout/generic/GenerateFrameLists.py
index d1ebf061d485..51c06dd13bb3 100644
--- a/layout/generic/GenerateFrameLists.py
+++ b/layout/generic/GenerateFrameLists.py
@@ -36,4 +36,4 @@ def generate_frame_type_list_h(output, *ignore):
     groups = grouped_frame_classes()
     output.write(HEADER)
     for group in groups:
-        output.write("FRAME_TYPE(%s)\n" % group[0].ty)
+        output.write("FRAME_TYPE(%s, %s, %s)\n" % (group[0].ty, group[0].cls, group[-1].cls))
diff --git a/layout/generic/nsIFrame.h b/layout/generic/nsIFrame.h
index 4800e8960f33..753b5155481e 100644
--- a/layout/generic/nsIFrame.h
+++ b/layout/generic/nsIFrame.h
@@ -169,7 +169,7 @@ class Selection;
 namespace mozilla {
 
 enum class LayoutFrameType : uint8_t {
-#define FRAME_TYPE(ty_) ty_,
+#define FRAME_TYPE(ty_, ...) ty_,
 #include "mozilla/FrameTypeList.h"
 #undef FRAME_TYPE
 };
@@ -2795,13 +2795,23 @@ class nsIFrame : public nsQueryFrame {
     return sLayoutFrameTypes[uint8_t(mClass)];
   }
 
-#define FRAME_TYPE(name_)                             \
-  bool Is##name_##Frame() const {                     \
-    return Type() == mozilla::LayoutFrameType::name_; \
+#ifdef __GNUC__
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Wtype-limits"
+#endif
+
+#define FRAME_TYPE(name_, first_class_, last_class_)                 \
+  bool Is##name_##Frame() const {                                    \
+    return uint8_t(mClass) >= uint8_t(ClassID::first_class_##_id) && \
+           uint8_t(mClass) <= uint8_t(ClassID::last_class_##_id);    \
   }
 #include "mozilla/FrameTypeList.h"
 #undef FRAME_TYPE
 
+#ifdef __GNUC__
+#  pragma GCC diagnostic pop
+#endif
+
   /**
    * Returns a transformation matrix that converts points in this frame's
    * coordinate space to points in some ancestor frame's coordinate space.