[Webkit-unassigned] [Bug 247454] New: Reduce aliasing of Wasm::Type type index field

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=247454

            Bug ID: 247454
           Summary: Reduce aliasing of Wasm::Type type index field
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Enhancement
          Priority: P2
         Component: WebAssembly
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: d_degazio at apple.com
                CC: d_degazio at apple.com,
                    webkit-bug-importer at group.apple.com

The Wasm::Type data structure generated in JavaScriptCore/wasm/generateWasmOpsHeader.py contains a TypeIndex field, which is currently used to store any of the following:
 - TypeDefinition::invalidIndex, for simple/primitive types
 - A TypeKind, specifically Funcref or Externref, used to implement those types when typed function references are enabled
 - A pointer to a TypeDefinition, for compound types like functions or structs

We currently lose 7/16 bytes of Wasm::Type to padding, so it'd be nice to use some of that space (or maybe refactor Wasm::Type in general) to separate these values out into other fields or a union type so we aren't reinterpreting this uintptr_t all the time.

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