• 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
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