From 2f9550d600e1c2b10e85e4ce00749ab1a160344e Mon Sep 17 00:00:00 2001
From: Jon Coppeard <jcoppeard@mozilla.com>
Date: Tue, 24 Feb 2015 09:40:02 +0000
Subject: [PATCH] Bug 1135100 - Don't bother to check if things we don't
 relocate have been forwarded r=terrence

---
 js/src/jsgc.cpp | 11 +++++++++++
 js/src/jsgc.h   | 25 +++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/js/src/jsgc.cpp b/js/src/jsgc.cpp
index f4faaa2abc16..c291df45d850 100644
--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -1935,6 +1935,12 @@ CanRelocateAllocKind(AllocKind kind)
     return kind <= FINALIZE_OBJECT_LAST;
 }
 
+static bool
+CanRelocateTraceKind(JSGCTraceKind kind)
+{
+    return kind == JSTRACE_OBJECT;
+}
+
 
 size_t ArenaHeader::countFreeCells()
 {
@@ -2249,6 +2255,11 @@ void
 MovingTracer::Visit(JSTracer *jstrc, void **thingp, JSGCTraceKind kind)
 {
     TenuredCell *thing = TenuredCell::fromPointer(*thingp);
+    if (!CanRelocateTraceKind(kind)) {
+        MOZ_ASSERT(!IsForwarded(thing));
+        return;
+    }
+
     Zone *zone = thing->zoneFromAnyThread();
     if (!zone->isGCCompacting()) {
         MOZ_ASSERT(!IsForwarded(thing));
diff --git a/js/src/jsgc.h b/js/src/jsgc.h
index 1e0bd41c7f85..a49bc4720553 100644
--- a/js/src/jsgc.h
+++ b/js/src/jsgc.h
@@ -1186,11 +1186,36 @@ class RelocationOverlay
 
 /* Functions for checking and updating things that might be moved by compacting GC. */
 
+#define TYPE_MIGHT_BE_FORWARDED(T, value)                                     \
+    inline bool                                                               \
+    TypeMightBeForwarded(T *thing)                                            \
+    {                                                                         \
+        return value;                                                         \
+    }                                                                         \
+
+TYPE_MIGHT_BE_FORWARDED(Cell, true)
+TYPE_MIGHT_BE_FORWARDED(JSObject, true)
+TYPE_MIGHT_BE_FORWARDED(JSString, false)
+TYPE_MIGHT_BE_FORWARDED(JS::Symbol, false)
+TYPE_MIGHT_BE_FORWARDED(JSScript, false)
+TYPE_MIGHT_BE_FORWARDED(Shape, false)
+TYPE_MIGHT_BE_FORWARDED(BaseShape, false)
+TYPE_MIGHT_BE_FORWARDED(jit::JitCode, false)
+TYPE_MIGHT_BE_FORWARDED(LazyScript, false)
+TYPE_MIGHT_BE_FORWARDED(ObjectGroup, false)
+
+#undef TYPE_MIGHT_BE_FORWARDED
+
 template <typename T>
 inline bool
 IsForwarded(T *t)
 {
     RelocationOverlay *overlay = RelocationOverlay::fromCell(t);
+    if (!TypeMightBeForwarded(t)) {
+        MOZ_ASSERT(!overlay->isForwarded());
+        return false;
+    }
+
     return overlay->isForwarded();
 }