Module sdpa_decode 

GPU SDPA decode kernel — F32 Q/K/V, multi-simdgroup tiled, single-token decode.

The kernel divides the KV sequence across N_SG simdgroups that each scan an independent KV chunk and produce a local (max, sum, unnorm_acc) triple. Simdgroup 0 then merges all N_SG partial results using the log-sum-exp combination rule and writes the final F32 output.

Constraints

• seq_len must be 1 (decode path only)
• head_dim must be a multiple of 32 (128, 256, 512 are supported)
• Q/K/V must be F32
• n_sg must be 1, 2, or 4

Statics

SDPA_DECODE_SHADER_SOURCE

Metal shader source.

Functions

dispatch_sdpa_decode

Dispatch the tiled decode SDPA kernel.

register

Register sdpa_decode pipeline.