[torque] add references to HeapObject fields.
This adds references to HeapObject fields to Torque. The syntax is based on Rust (which is essentially C pointer syntax). The type &T is a reference to T (which must be a scalar type for now). We can create references from field access expressions, using the addressof(&) operator: &obj.fieldname To read or assign a reference, we use the dereference(*) operator: *someref = *otherref This CL also uses references internally normal class field accesses, but only if there is no overload for field accessor functions. This allows to have overloaded field accessors for a subtype like FastJSArray. However, there is a change in behavior in that an operator ".fieldname" will stop reference creation and will therefore also stop write access to a class field of the same name. That's why this CL had to add a write overload ".length=" for FastJSArray. References desugar to a pair of a tagged HeapObject pointer and an untagged offset into this HeapObject. On the CSA-side, they are represented by the C++ struct struct TorqueReference { TNode<HeapObject> object; TNode<IntPtrT> offset; }; Bug: v8:7793 Change-Id: Ica6468d47847bd68fb6b85f731cf8fbe142fa401 Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1557151 Commit-Queue: Tobias Tebbi <tebbi@chromium.org> Reviewed-by: Sigurd Schneider <sigurds@chromium.org> Cr-Commit-Position: refs/heads/master@{#60780}
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