1. 03 Mar, 2020 1 commit
    • Joyee Cheung's avatar
      [class] maintain private brand information on SFI · 0753cbea
      Joyee Cheung authored
      When an empty class is nested inside a class with private instance
      methods, like this:
      
        class Outer {
          constructor() {}
          #method() {}
          factory() {
            class Inner {
              constructor() {  }
            }
            return Inner;
          }
          run(obj) {
            obj.#method();
          }
        }
      
      The bytecode generator previously generate private brand
      initialization for the constructor of Inner by mistake,
      because during scope chain serialization/deserialization,
      the outer scopes of Inner and factory() are not allocated
      or serialized (as they are empty). In the eyes of the bytecode
      generator, it then appeared as if Outer is the direct outer
      scope of Inner's constructor.
      
      In order to work around this information loss, in this patch
      we rely on SharedFunctionInfo instead of the Context/ScopeInfo
      chain to maintain the information about private brand initialization.
      This is done by shrinking expected_nof_properties to 8 bits and
      freeing 8 bits for a second bitfield on the SFI.
      
      Design doc: https://docs.google.com/document/d/14maU596YbHcWR7XR-_iXM_ANhAAmiuRlJZysM61lqaE/edit#
      Bug: v8:9839, v8:8330, v8:10098
      
      Change-Id: I4370a0459bfc0da388052ad5a91aac59582d811d
      Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2056889
      Commit-Queue: Joyee Cheung <joyee@igalia.com>
      Reviewed-by: 's avatarLeszek Swirski <leszeks@chromium.org>
      Reviewed-by: 's avatarToon Verwaest <verwaest@chromium.org>
      Cr-Commit-Position: refs/heads/master@{#66575}
      0753cbea