• Anton Bikineev's avatar
    cppgc: Force EBO to always work with GCed · 92eae6d1
    Anton Bikineev authored
    Currently, in the following struct
    
    struct LayoutObject : GarbageCollected<>, MixinA, MixinB {};
    
    the subobject that corresponds to the first base GarbageCollected<>
    always takes up some space (one word). The empty-base-optimization
    doesn't happen because the second base (MixinA) has the same subobject
    as the first base (GarbageCollected), which is the most parent class
    GarbageCollectedBase. The compiler can't "merge" them because it must
    guarantee that distinct objects of the same type have distinct
    addresses.
    
    The attribute [[no_unique_address]] doesn't work for base classes,
    unfortunately (but is a good idea for a Standard proposal). As a
    solution, the CL simply removes GarbageCollectedBase.
    
    Bug: chromium:1260797
    Change-Id: I415b10a5fbcebce3d6ee97b8870ea9ae90f383a8
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3259654
    Commit-Queue: Anton Bikineev <bikineev@chromium.org>
    Reviewed-by: 's avatarMichael Lippautz <mlippautz@chromium.org>
    Cr-Commit-Position: refs/heads/main@{#77693}
    92eae6d1
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