[turbofan] Do not force initial map creation.

Forcing it seems unnecessary and hinders concurrent compilation.

Also turn a related condition into a CHECK.

Bug: v8:7790
Change-Id: Ie7d7e47e6bc2743d742cfe07e65436c1b8b994f3
Reviewed-on: https://chromium-review.googlesource.com/1177705Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55164}

src/compiler/js-create-lowering.cc

@@ -44,8 +44,9 @@ Node* GetArgumentsFrameState(Node* frame_state) {
 // inlined.
 bool IsAllocationInlineable(const JSFunctionRef& target,
                             const JSFunctionRef& new_target) {
+  CHECK_IMPLIES(new_target.has_initial_map(),
+                !new_target.initial_map().is_dictionary_map());
   return new_target.has_initial_map() &&
-         !new_target.initial_map().is_dictionary_map() &&
          new_target.initial_map().constructor_or_backpointer().equals(target);
 }
 
@@ -412,7 +413,7 @@ Reduction JSCreateLowering::ReduceJSCreateGeneratorObject(Node* node) {
     DCHECK(closure_type.AsHeapConstant()->Ref().IsJSFunction());
     JSFunctionRef js_function =
         closure_type.AsHeapConstant()->Ref().AsJSFunction();
-    js_function.EnsureHasInitialMap();
+    if (!js_function.has_initial_map()) return NoChange();
 
     SlackTrackingPrediction slack_tracking_prediction =
         dependencies()->DependOnInitialMapInstanceSizePrediction(js_function);

src/compiler/js-native-context-specialization.cc

@@ -411,10 +411,9 @@ Reduction JSNativeContextSpecialization::ReduceJSOrdinaryHasInstance(
     if (function->IsConstructor() && function->has_prototype_slot() &&
         function->has_instance_prototype() &&
         function->prototype()->IsJSReceiver()) {
-      // Ensure that the {function} has a valid initial map, so we can
-      // depend on that for the prototype constant-folding below.
-      JSFunction::EnsureHasInitialMap(function);
-
+      // We need {function}'s initial map so that we can depend on it for the
+      // prototype constant-folding below.
+      if (!function->has_initial_map()) return NoChange();
       MapRef initial_map = dependencies()->DependOnInitialMap(
           JSFunctionRef(js_heap_broker(), function));
       Node* prototype = jsgraph()->Constant(
@@ -1104,11 +1103,13 @@ Reduction JSNativeContextSpecialization::ReduceJSLoadNamed(Node* node) {
         p.name().is_identical_to(factory()->prototype_string())) {
       // Optimize "prototype" property of functions.
       Handle<JSFunction> function = Handle<JSFunction>::cast(m.Value());
+      if (!function->has_prototype_slot() || !function->has_initial_map()) {
+        return NoChange();
+      }
       if (!function->PrototypeRequiresRuntimeLookup()) {
         // We need to add a code dependency on the initial map of the
         // {function} in order to be notified about changes to the
         // "prototype" of {function}.
-        JSFunction::EnsureHasInitialMap(function);
         dependencies()->DependOnInitialMap(
             JSFunctionRef(js_heap_broker(), function));
         Handle<Object> prototype(function->prototype(), isolate());