// Conv2d forward via implicit GEMM — small-tile variant.
// BM=32, BN=32, KTILE=16, TM=2, TN=2, workgroup [16,16,1]
// 4× more workgroups than the 64×64 variant for better occupancy on small matrices.
//
// Dispatch: [ceil(oH*oW / 32), ceil(Co / 32), batch]
struct Params {
batch: u32,
in_channels: u32,
in_h: u32,
in_w: u32,
out_channels: u32,
kernel_h: u32,
kernel_w: u32,
stride: u32,
padding_h: u32,
out_h: u32,
out_w: u32,
padding_w: u32,
}
var<storage> src: array<f32>;
var<storage> weight: array<f32>;
var<storage, read_write> dst: array<f32>;
var<uniform> params: Params;
var<workgroup> shared_a: array<f32, 512>; // 32 * 16
var<workgroup> shared_b: array<f32, 512>; // 16 * 32
@compute @workgroup_size(16, 16)
fn main(@builtin(workgroup_id) wgid: vec3<u32>, @builtin(local_invocation_id) lid: vec3<u32>) {
let tx = lid.x;
let ty = lid.y;
let n = wgid.z;
let tile_row = wgid.y * 32u;
let tile_col = wgid.x * 32u;
let tid = ty * 16u + tx;
let k_total = params.in_channels * params.kernel_h * params.kernel_w;
let n_total = params.out_h * params.out_w;
let m_total = params.out_channels;
let input_stride = params.in_channels * params.in_h * params.in_w;
let kernel_hw = params.kernel_h * params.kernel_w;
var s0_0 = 0.0; var s0_1 = 0.0;
var s1_0 = 0.0; var s1_1 = 0.0;
var t = 0u;
loop {
if t >= k_total { break; }
// Load A tile: weight[Co, K] → shared_a[32, 16]
for (var e = 0u; e < 2u; e++) {
let flat = tid + e * 256u;
let row_local = flat / 16u;
let col_local = flat % 16u;
let a_row = tile_row + row_local;
let a_col = t + col_local;
let ib = a_row < m_total && a_col < k_total;
shared_a[row_local * 16u + col_local] = select(0.0, weight[a_row * k_total + a_col], ib);
}
// Load B tile: im2col(input)^T [K, oH*oW] → shared_b[16, 32]
for (var e = 0u; e < 2u; e++) {
let flat = tid + e * 256u;
let row_local = flat / 32u;
let col_local = flat % 32u;
let k_idx = t + row_local;
let hw_idx = tile_col + col_local;
var val = 0.0;
if k_idx < k_total && hw_idx < n_total {
let ci = k_idx / kernel_hw;
let k_rem = k_idx - ci * kernel_hw;
let kh = k_rem / params.kernel_w;
let kw = k_rem - kh * params.kernel_w;
let oh = hw_idx / params.out_w;
let ow = hw_idx - oh * params.out_w;
let ih = i32(oh * params.stride + kh) - i32(params.padding_h);
let iw = i32(ow * params.stride + kw) - i32(params.padding_w);
if ih >= 0 && u32(ih) < params.in_h && iw >= 0 && u32(iw) < params.in_w {
val = src[n * input_stride + ci * params.in_h * params.in_w + u32(ih) * params.in_w + u32(iw)];
}
}
shared_b[row_local * 32u + col_local] = val;
}
workgroupBarrier();
for (var kk = 0u; kk < 16u; kk++) {
let a0 = shared_a[(ty * 2u + 0u) * 16u + kk];
let a1 = shared_a[(ty * 2u + 1u) * 16u + kk];
let b0 = shared_b[kk * 32u + tx * 2u + 0u];
let b1 = shared_b[kk * 32u + tx * 2u + 1u];
s0_0 += a0 * b0; s0_1 += a0 * b1;
s1_0 += a1 * b0; s1_1 += a1 * b1;
}
workgroupBarrier();
t += 16u;
}
let output_stride = m_total * n_total;
let s = array<array<f32, 2>, 2>(
array<f32, 2>(s0_0, s0_1),
array<f32, 2>(s1_0, s1_1),
);
for (var i = 0u; i < 2u; i++) {
for (var j = 0u; j < 2u; j++) {
let co = tile_row + ty * 2u + i;
let hw = tile_col + tx * 2u + j;
if co < m_total && hw < n_total {
dst[n * output_stride + co * n_total + hw] = s[i][j];
}
}
}
}