D466 - Narrow typed-buffer formats decode through a dedicated packed path

Status: decided Date: 2026-09-02

A typed-buffer access whose components are narrower than a word decodes through a separate packed-buffer path, extended one component kind at a time, rather than through the plain per-dword path or being refused outright.

Why: a packed format stores several components inside one word, which the plain path cannot address, and a wrong conversion renders silently rather than failing. Each kind is verified against a real device before the next is added, since that is the only way to catch a wrong conversion here.

Rejected:

• Refusing every narrow format outright: correct but leaves a whole class of shaders unsupported with no path to close the gap.
• Extending the plain per-dword path to also unpack fields: conflates two different memory layouts in one function.