[wasm] Improve precision of slow DCHECK for WebAssembly-constructed internal objects.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 6dbd0d32cba21d02228f5019a051fdf063306074..e3617bcb2a18b74fdf79598ff31f4ca1f9d79968 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -15857,23 +15857,27 @@ bool JSObject::WasConstructedFromApiFunction() {
   auto instance_type = map()->instance_type();
   bool is_api_object = instance_type == JS_API_OBJECT_TYPE ||
                        instance_type == JS_SPECIAL_API_OBJECT_TYPE;
+  bool is_wasm_object =
+      instance_type == WASM_MEMORY_TYPE || instance_type == WASM_MODULE_TYPE ||
+      instance_type == WASM_INSTANCE_TYPE || instance_type == WASM_TABLE_TYPE;
 #ifdef ENABLE_SLOW_DCHECKS
   if (FLAG_enable_slow_asserts) {
     Object* maybe_constructor = map()->GetConstructor();
     if (maybe_constructor->IsJSFunction()) {
       JSFunction* constructor = JSFunction::cast(maybe_constructor);
-      if (constructor->shared()->IsApiFunction()) {
-        DCHECK(is_api_object);
-      } else {
-        DCHECK(!is_api_object);
-      }
+      DCHECK_EQ(constructor->shared()->IsApiFunction(),
+                is_api_object || is_wasm_object);
     } else if (maybe_constructor->IsFunctionTemplateInfo()) {
-      DCHECK(is_api_object);
+      DCHECK(is_api_object || is_wasm_object);
     } else {
       return false;
     }
   }
 #endif
+  // TODO(titzer): Clean this up somehow. WebAssembly objects should not be
+  // considered "constructed from API functions" even though they have
+  // function template info, since that would make the V8 GC identify them to

[ahaas, 2017/07/10 12:42:48]

What do you mean by the "would" here? Does it make the V8 GC identify them to
the embedder or not?

[titzer, 2017/07/10 13:16:46]

Without this change, the V8 GC (correctly) does not identify them to the
embedder. This change only affects the DCHECKS above, which were imprecise,
since WASM objects also use FunctionTemplateInfo.

+  // the embedder, e.g. the Oilpan GC.
   return is_api_object;
 }