From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Toon Verwaest <verwaest@chromium.org>
Date: Fri, 16 Jun 2023 17:13:52 +0200
Subject: Merged: [runtime] Set instance prototypes directly on maps

Bug: chromium:1452137
(cherry picked from commit c7c447735f762f6d6d0878e229371797845ef4ab)

Change-Id: I611c41f942e2e51f3c4b4f1d119c18410617188e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/4637888
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Auto-Submit: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/branch-heads/11.4@{#47}
Cr-Branched-From: 8a8a1e7086dacc426965d3875914efa66663c431-refs/heads/11.4.183@{#1}
Cr-Branched-From: 5483d8e816e0bbce865cbbc3fa0ab357e6330bab-refs/heads/main@{#87241}

diff --git a/src/objects/js-function.cc b/src/objects/js-function.cc
index 6f9b2f676ac5d3f91589a78344b27765dc8bef06..d50743b1c73ad3304c5c5c22a4e0589cca302502 100644
--- a/src/objects/js-function.cc
+++ b/src/objects/js-function.cc
@@ -676,6 +676,10 @@ void SetInstancePrototype(Isolate* isolate, Handle<JSFunction> function,
       // At that point, a new initial map is created and the prototype is put
       // into the initial map where it belongs.
       function->set_prototype_or_initial_map(*value, kReleaseStore);
+      if (value->IsJSObjectThatCanBeTrackedAsPrototype()) {
+        // Optimize as prototype to detach it from its transition tree.
+        JSObject::OptimizeAsPrototype(Handle<JSObject>::cast(value));
+      }
     } else {
       Handle<Map> new_map =
           Map::Copy(isolate, initial_map, "SetInstancePrototype");
@@ -801,8 +805,10 @@ void JSFunction::EnsureHasInitialMap(Handle<JSFunction> function) {
   Handle<HeapObject> prototype;
   if (function->has_instance_prototype()) {
     prototype = handle(function->instance_prototype(), isolate);
+    map->set_prototype(*prototype);
   } else {
     prototype = isolate->factory()->NewFunctionPrototype(function);
+    Map::SetPrototype(isolate, map, prototype);
   }
   DCHECK(map->has_fast_object_elements());
 
