convert_unary handles the contiguous case through the general strided kernel,
one element per thread: each lane reads 4 bytes and writes 2. Converting the
activations for a bf16 matrix multiplication that way moves 126 MB in 1021 us
on gfx1151, about 65% of what the memory system can do.
Give the contiguous path its own kernel that takes four elements per thread
through a vector type, so a warp loads 512 bytes at a time instead of 128. It
is used only when the element count is a multiple of four and both pointers
carry the alignment the vector type needs, and falls back to the strided
kernel otherwise.
Model level, Qwen3.8-Next-Flash IQ3_XXS on gfx1151, llama-bench -ub 2048 -r 6,
mean of the last 3 reps, ABBA counterbalanced:
pp2048 688.0 680.0 -> 694.3 691.1 +1.26%
tg128 24.8 24.8 -> 24.8 24.8 +0.14%
Every conversion in a prefill takes the new kernel (kernel trace: 1146
convert_unary_cont_vec4, no convert_unary). Output is bit identical; MUL_MAT,
MUL_MAT_ID, CPY, CONT, GET_ROWS and SET_ROWS pass.
Assisted-by: Claude Opus 5
f4e276a206