• Tobias Tebbi's avatar
    [torque] shape: define in-object properties properly · cfab6505
    Tobias Tebbi authored
    This introduces a new keyword "shape" in addition to "class",
    which allows the definition of a type that extends a JSObject
    subclass and specifies one or several maps with statically
    known in-object properties.
    Differences compared to normal classes:
    - Shapes are transient since they specify maps instead of
      instance types.
    - Shapes have a known size.
    - Fields of shapes are always in-object properties. In particular,
      this means that their offset is after kHeaderSize.
    - It's forbidden to inherited from shapes.
    - Since shapes usually specify NativeContext-dependent maps, it's
      not possible to write runtime type-checks for them. Thus this CL
      avoids mapping them to their own TNode type, as the CAST macro
      won't work properly. We had runtime-checks for some of them
      nevertheless, some of them scarily confusing like
      IsJSSloppyArgumentsObject, that actually just checked the instance
      type.
    
    Drive-by cleanups and simplifications:
    - Allow subclassing from non-abstract classes and remove
      @dirtyInstantiatedAbstractClass. This attribute stems from a mis-
      conception of how instance types work, and with this change it
      ceases to have semantic influence.
    - Replace the existing JSArgumentsObject subclasses into two shapes.
      JSArgumentsObjectWithLength had to be removed since shapes don't
      support subclassing.
    - Place kHeaderSize correctly for objects with indexed fields.
    
    Design doc:
    https://docs.google.com/document/d/1zPy2ZYfNFjeEuw6Mz3YJA-GaPGbdcSYam3SrS7ETzRU
    
    Bug: v8:8944
    
    Change-Id: Iabf185ccd27d0900e0890539a7fe9eaa8bf2d50e
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1917140
    Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
    Reviewed-by: 's avatarNico Hartmann <nicohartmann@chromium.org>
    Reviewed-by: 's avatarJakob Gruber <jgruber@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#65108}
    cfab6505
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