Pref the use of unboxed plain objects in JS and disable by default.

This should be all that's needed for #1017, but verification of
impact is definitely desired.

4 files changed, 21 insertions, 13 deletions

diff --git a/js/src/jit/JitOptions.cpp b/js/src/jit/JitOptions.cpp
index eb5a6c1c22..b9a7c7b276 100644
--- a/js/src/jit/JitOptions.cpp
+++ b/js/src/jit/JitOptions.cpp
@@ -222,7 +222,7 @@ DefaultJitOptions::DefaultJitOptions()
     }
 
     // Toggles whether unboxed plain objects can be created by the VM.
-    SET_DEFAULT(disableUnboxedObjects, false);
+    SET_DEFAULT(disableUnboxedObjects, true);
 
     // Test whether Atomics are allowed in asm.js code.
     SET_DEFAULT(asmJSAtomicsEnable, false);
diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index 37d023bd4a..6114b81576 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -6410,6 +6410,9 @@ JS_SetGlobalJitCompilerOption(JSContext* cx, JSJitCompilerOption opt, uint32_t v
         }
         jit::JitOptions.jumpThreshold = value;
         break;
+      case JSJITCOMPILER_UNBOXED_OBJECTS:
+        jit::JitOptions.disableUnboxedObjects = !value;
+        break;
       case JSJITCOMPILER_ASMJS_ATOMICS_ENABLE:
         jit::JitOptions.asmJSAtomicsEnable = !!value;
         break;
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index 005d2278e4..1f726f2e54 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -5783,19 +5783,20 @@ JS_SetParallelParsingEnabled(JSContext* cx, bool enabled);
 extern JS_PUBLIC_API(void)
 JS_SetOffthreadIonCompilationEnabled(JSContext* cx, bool enabled);
 
-#define JIT_COMPILER_OPTIONS(Register)                                     \
-    Register(BASELINE_WARMUP_TRIGGER, "baseline.warmup.trigger")           \
-    Register(ION_WARMUP_TRIGGER, "ion.warmup.trigger")                     \
-    Register(ION_GVN_ENABLE, "ion.gvn.enable")                             \
-    Register(ION_FORCE_IC, "ion.forceinlineCaches")                        \
-    Register(ION_ENABLE, "ion.enable")                                     \
+#define JIT_COMPILER_OPTIONS(Register)                                      \
+    Register(BASELINE_WARMUP_TRIGGER, "baseline.warmup.trigger")            \
+    Register(ION_WARMUP_TRIGGER, "ion.warmup.trigger")                      \
+    Register(ION_GVN_ENABLE, "ion.gvn.enable")                              \
+    Register(ION_FORCE_IC, "ion.forceinlineCaches")                         \
+    Register(ION_ENABLE, "ion.enable")                                      \
     Register(ION_INTERRUPT_WITHOUT_SIGNAL, "ion.interrupt-without-signals") \
-    Register(ION_CHECK_RANGE_ANALYSIS, "ion.check-range-analysis")         \
-    Register(BASELINE_ENABLE, "baseline.enable")                           \
-    Register(OFFTHREAD_COMPILATION_ENABLE, "offthread-compilation.enable") \
-    Register(JUMP_THRESHOLD, "jump-threshold")                             \
-    Register(ASMJS_ATOMICS_ENABLE, "asmjs.atomics.enable")                 \
-    Register(WASM_TEST_MODE, "wasm.test-mode")                             \
+    Register(ION_CHECK_RANGE_ANALYSIS, "ion.check-range-analysis")          \
+    Register(BASELINE_ENABLE, "baseline.enable")                            \
+    Register(OFFTHREAD_COMPILATION_ENABLE, "offthread-compilation.enable")  \
+    Register(JUMP_THRESHOLD, "jump-threshold")                              \
+    Register(UNBOXED_OBJECTS, "unboxed_objects")                            \
+    Register(ASMJS_ATOMICS_ENABLE, "asmjs.atomics.enable")                  \
+    Register(WASM_TEST_MODE, "wasm.test-mode")                              \
     Register(WASM_FOLD_OFFSETS, "wasm.fold-offsets")
 
 typedef enum JSJitCompilerOption {
diff --git a/js/xpconnect/src/XPCJSContext.cpp b/js/xpconnect/src/XPCJSContext.cpp
index 0243d80e36..bde949a960 100644
--- a/js/xpconnect/src/XPCJSContext.cpp
+++ b/js/xpconnect/src/XPCJSContext.cpp
@@ -1427,6 +1427,8 @@ ReloadPrefsCallback(const char* pref, void* data)
 
     bool extraWarnings = Preferences::GetBool(JS_OPTIONS_DOT_STR "strict");
 
+    bool unboxedObjects = Preferences::GetBool(JS_OPTIONS_DOT_STR "unboxed_objects");
+    
     sSharedMemoryEnabled = Preferences::GetBool(JS_OPTIONS_DOT_STR "shared_memory");
 
 #ifdef DEBUG
@@ -1455,6 +1457,8 @@ ReloadPrefsCallback(const char* pref, void* data)
                                   useBaselineEager ? 0 : -1);
     JS_SetGlobalJitCompilerOption(cx, JSJITCOMPILER_ION_WARMUP_TRIGGER,
                                   useIonEager ? 0 : -1);
+    JS_SetGlobalJitCompilerOption(cx, JSJITCOMPILER_UNBOXED_OBJECTS,
+                                  unboxedObjects);
 }
 
 XPCJSContext::~XPCJSContext()