D145 - Wavefront width is supplied, not inferred

Status: decided Date: 2026-09-26

Strategy::Predicated carries a wavefront width, defaulting to 64, supplied by the caller from the pipeline state. Mask instructions write through the mask at either width. Probes are assembled in 64-lane mode, because width does not change the encodings.

Why: nothing in the instruction stream states the width, and inferring it from which mask instructions appear guesses from an absence. A 32-lane shader narrows its mask with 32-bit scalar instructions, which must reach the mask rather than an ordinary register.

Rejected:

• Inferring width from the shader: fails for any shader that has not yet touched its mask.
• Separate tables per width: the encodings are identical.