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// ---------------------------------------------------------------------------
// NEON tiled matmul_bt — cache-blocked with 4×8 NEON microkernel
// ---------------------------------------------------------------------------
//
// Microkernel design (4i × 8j):
// - 32 float32x4_t accumulators (4 rows × 8 cols)
// - Inner k-loop unrolled 2× (processes 8 k-values per iteration)
// - B vectors loaded once per k-chunk, reused across all 4 i-rows
// - Register budget: 8 B-vecs + 1 A-vec + 8 acc (current i) = 17 live regs
// (remaining 15 hold acc for other i-rows or are spill slots)
//
#[cfg(all(target_arch = "aarch64", not(target_os = "macos")))]
use super::tiled::{TILE_I, TILE_J, TILE_K};
#[cfg(all(target_arch = "aarch64", not(target_os = "macos")))]
#[target_feature(enable = "neon")]
pub(super) unsafe fn matmul_bt_tiled_neon(
a: &[f32],
b: &[f32],
c: &mut [f32],
m: usize,
k: usize,
n: usize,
) {
use std::arch::aarch64::*;
let a_ptr = a.as_ptr();
let b_ptr = b.as_ptr();
let c_ptr = c.as_mut_ptr();
// Loop order: J-tiles → I-tiles → K-tiles
// B tiles stay hot in cache across all I iterations.
let mut j_start = 0;
while j_start < n {
let j_end = (j_start + TILE_J).min(n);
let j_count = j_end - j_start;
let mut i_start = 0;
while i_start < m {
let i_end = (i_start + TILE_I).min(m);
let i_count = i_end - i_start;
let mut k_start = 0;
while k_start < k {
let k_end = (k_start + TILE_K).min(k);
let k_len = k_end - k_start;
// Fast path: full 4×8 tile with k_len >= 8 (enables 2× unrolled inner loop)
if i_count == TILE_I && j_count == TILE_J && k_len >= 8 {
// SAFETY: We have verified i_count == 4 and j_count == 8.
// All pointer arithmetic stays within bounds of a (m*k), b (n*k), c (m*n):
// - i ranges from i_start to i_start+3, each < m
// - j ranges from j_start to j_start+7, each < n
// - k offsets range from k_start to k_end-1, each < k
// - NEON loads read 4 contiguous f32s; offset+3 < k for all loads
// 4×8 accumulator grid: each acc[ii][jj] holds partial dot products
// across 4 lanes of the K-dimension. After the k-loop, each is
// horizontally summed to produce the scalar C[i][j] contribution.
let mut acc0 = [vdupq_n_f32(0.0); TILE_J];
let mut acc1 = [vdupq_n_f32(0.0); TILE_J];
let mut acc2 = [vdupq_n_f32(0.0); TILE_J];
let mut acc3 = [vdupq_n_f32(0.0); TILE_J];
// Precompute row base pointers for the 4 A-rows and 8 B-rows.
let a0_base = a_ptr.add(i_start * k);
let a1_base = a_ptr.add((i_start + 1) * k);
let a2_base = a_ptr.add((i_start + 2) * k);
let a3_base = a_ptr.add((i_start + 3) * k);
let b0_base = b_ptr.add(j_start * k);
let b1_base = b_ptr.add((j_start + 1) * k);
let b2_base = b_ptr.add((j_start + 2) * k);
let b3_base = b_ptr.add((j_start + 3) * k);
let b4_base = b_ptr.add((j_start + 4) * k);
let b5_base = b_ptr.add((j_start + 5) * k);
let b6_base = b_ptr.add((j_start + 6) * k);
let b7_base = b_ptr.add((j_start + 7) * k);
// Main loop: process 8 k-values per iteration (2× unrolled).
// Each iteration does 2 rounds of 4-wide NEON FMA.
let k_pairs = k_len / 8;
for kp in 0..k_pairs {
let ko = k_start + kp * 8;
// Prefetch the next k-chunk's B-rows into L1 cache while
// the current chunk is being processed by the FMA units.
if kp + 1 < k_pairs {
let next_ko = ko + 8;
core::arch::asm!(
"prfm pldl1keep, [{0}]",
"prfm pldl1keep, [{1}]",
"prfm pldl1keep, [{2}]",
"prfm pldl1keep, [{3}]",
"prfm pldl1keep, [{4}]",
"prfm pldl1keep, [{5}]",
"prfm pldl1keep, [{6}]",
"prfm pldl1keep, [{7}]",
in(reg) b0_base.add(next_ko),
in(reg) b1_base.add(next_ko),
in(reg) b2_base.add(next_ko),
in(reg) b3_base.add(next_ko),
in(reg) b4_base.add(next_ko),
in(reg) b5_base.add(next_ko),
in(reg) b6_base.add(next_ko),
in(reg) b7_base.add(next_ko),
options(nostack, preserves_flags, readonly),
);
}
// --- First group of 4 k-values ---
let bv0a = vld1q_f32(b0_base.add(ko));
let bv1a = vld1q_f32(b1_base.add(ko));
let bv2a = vld1q_f32(b2_base.add(ko));
let bv3a = vld1q_f32(b3_base.add(ko));
let bv4a = vld1q_f32(b4_base.add(ko));
let bv5a = vld1q_f32(b5_base.add(ko));
let bv6a = vld1q_f32(b6_base.add(ko));
let bv7a = vld1q_f32(b7_base.add(ko));
let av = vld1q_f32(a0_base.add(ko));
acc0[0] = vfmaq_f32(acc0[0], av, bv0a);
acc0[1] = vfmaq_f32(acc0[1], av, bv1a);
acc0[2] = vfmaq_f32(acc0[2], av, bv2a);
acc0[3] = vfmaq_f32(acc0[3], av, bv3a);
acc0[4] = vfmaq_f32(acc0[4], av, bv4a);
acc0[5] = vfmaq_f32(acc0[5], av, bv5a);
acc0[6] = vfmaq_f32(acc0[6], av, bv6a);
acc0[7] = vfmaq_f32(acc0[7], av, bv7a);
let av = vld1q_f32(a1_base.add(ko));
acc1[0] = vfmaq_f32(acc1[0], av, bv0a);
acc1[1] = vfmaq_f32(acc1[1], av, bv1a);
acc1[2] = vfmaq_f32(acc1[2], av, bv2a);
acc1[3] = vfmaq_f32(acc1[3], av, bv3a);
acc1[4] = vfmaq_f32(acc1[4], av, bv4a);
acc1[5] = vfmaq_f32(acc1[5], av, bv5a);
acc1[6] = vfmaq_f32(acc1[6], av, bv6a);
acc1[7] = vfmaq_f32(acc1[7], av, bv7a);
let av = vld1q_f32(a2_base.add(ko));
acc2[0] = vfmaq_f32(acc2[0], av, bv0a);
acc2[1] = vfmaq_f32(acc2[1], av, bv1a);
acc2[2] = vfmaq_f32(acc2[2], av, bv2a);
acc2[3] = vfmaq_f32(acc2[3], av, bv3a);
acc2[4] = vfmaq_f32(acc2[4], av, bv4a);
acc2[5] = vfmaq_f32(acc2[5], av, bv5a);
acc2[6] = vfmaq_f32(acc2[6], av, bv6a);
acc2[7] = vfmaq_f32(acc2[7], av, bv7a);
let av = vld1q_f32(a3_base.add(ko));
acc3[0] = vfmaq_f32(acc3[0], av, bv0a);
acc3[1] = vfmaq_f32(acc3[1], av, bv1a);
acc3[2] = vfmaq_f32(acc3[2], av, bv2a);
acc3[3] = vfmaq_f32(acc3[3], av, bv3a);
acc3[4] = vfmaq_f32(acc3[4], av, bv4a);
acc3[5] = vfmaq_f32(acc3[5], av, bv5a);
acc3[6] = vfmaq_f32(acc3[6], av, bv6a);
acc3[7] = vfmaq_f32(acc3[7], av, bv7a);
// --- Second group of 4 k-values (unrolled) ---
let ko2 = ko + 4;
let bv0b = vld1q_f32(b0_base.add(ko2));
let bv1b = vld1q_f32(b1_base.add(ko2));
let bv2b = vld1q_f32(b2_base.add(ko2));
let bv3b = vld1q_f32(b3_base.add(ko2));
let bv4b = vld1q_f32(b4_base.add(ko2));
let bv5b = vld1q_f32(b5_base.add(ko2));
let bv6b = vld1q_f32(b6_base.add(ko2));
let bv7b = vld1q_f32(b7_base.add(ko2));
let av = vld1q_f32(a0_base.add(ko2));
acc0[0] = vfmaq_f32(acc0[0], av, bv0b);
acc0[1] = vfmaq_f32(acc0[1], av, bv1b);
acc0[2] = vfmaq_f32(acc0[2], av, bv2b);
acc0[3] = vfmaq_f32(acc0[3], av, bv3b);
acc0[4] = vfmaq_f32(acc0[4], av, bv4b);
acc0[5] = vfmaq_f32(acc0[5], av, bv5b);
acc0[6] = vfmaq_f32(acc0[6], av, bv6b);
acc0[7] = vfmaq_f32(acc0[7], av, bv7b);
let av = vld1q_f32(a1_base.add(ko2));
acc1[0] = vfmaq_f32(acc1[0], av, bv0b);
acc1[1] = vfmaq_f32(acc1[1], av, bv1b);
acc1[2] = vfmaq_f32(acc1[2], av, bv2b);
acc1[3] = vfmaq_f32(acc1[3], av, bv3b);
acc1[4] = vfmaq_f32(acc1[4], av, bv4b);
acc1[5] = vfmaq_f32(acc1[5], av, bv5b);
acc1[6] = vfmaq_f32(acc1[6], av, bv6b);
acc1[7] = vfmaq_f32(acc1[7], av, bv7b);
let av = vld1q_f32(a2_base.add(ko2));
acc2[0] = vfmaq_f32(acc2[0], av, bv0b);
acc2[1] = vfmaq_f32(acc2[1], av, bv1b);
acc2[2] = vfmaq_f32(acc2[2], av, bv2b);
acc2[3] = vfmaq_f32(acc2[3], av, bv3b);
acc2[4] = vfmaq_f32(acc2[4], av, bv4b);
acc2[5] = vfmaq_f32(acc2[5], av, bv5b);
acc2[6] = vfmaq_f32(acc2[6], av, bv6b);
acc2[7] = vfmaq_f32(acc2[7], av, bv7b);
let av = vld1q_f32(a3_base.add(ko2));
acc3[0] = vfmaq_f32(acc3[0], av, bv0b);
acc3[1] = vfmaq_f32(acc3[1], av, bv1b);
acc3[2] = vfmaq_f32(acc3[2], av, bv2b);
acc3[3] = vfmaq_f32(acc3[3], av, bv3b);
acc3[4] = vfmaq_f32(acc3[4], av, bv4b);
acc3[5] = vfmaq_f32(acc3[5], av, bv5b);
acc3[6] = vfmaq_f32(acc3[6], av, bv6b);
acc3[7] = vfmaq_f32(acc3[7], av, bv7b);
}
// Handle remaining 4-element chunk if k_len is not divisible by 8
// but is divisible by 4 (since k_len >= 8, we know k_pairs >= 1).
let k_vec_rem_start = k_start + k_pairs * 8;
if k_vec_rem_start + 4 <= k_end {
let ko = k_vec_rem_start;
let bv0 = vld1q_f32(b0_base.add(ko));
let bv1 = vld1q_f32(b1_base.add(ko));
let bv2 = vld1q_f32(b2_base.add(ko));
let bv3 = vld1q_f32(b3_base.add(ko));
let bv4 = vld1q_f32(b4_base.add(ko));
let bv5 = vld1q_f32(b5_base.add(ko));
let bv6 = vld1q_f32(b6_base.add(ko));
let bv7 = vld1q_f32(b7_base.add(ko));
let av = vld1q_f32(a0_base.add(ko));
acc0[0] = vfmaq_f32(acc0[0], av, bv0);
acc0[1] = vfmaq_f32(acc0[1], av, bv1);
acc0[2] = vfmaq_f32(acc0[2], av, bv2);
acc0[3] = vfmaq_f32(acc0[3], av, bv3);
acc0[4] = vfmaq_f32(acc0[4], av, bv4);
acc0[5] = vfmaq_f32(acc0[5], av, bv5);
acc0[6] = vfmaq_f32(acc0[6], av, bv6);
acc0[7] = vfmaq_f32(acc0[7], av, bv7);
let av = vld1q_f32(a1_base.add(ko));
acc1[0] = vfmaq_f32(acc1[0], av, bv0);
acc1[1] = vfmaq_f32(acc1[1], av, bv1);
acc1[2] = vfmaq_f32(acc1[2], av, bv2);
acc1[3] = vfmaq_f32(acc1[3], av, bv3);
acc1[4] = vfmaq_f32(acc1[4], av, bv4);
acc1[5] = vfmaq_f32(acc1[5], av, bv5);
acc1[6] = vfmaq_f32(acc1[6], av, bv6);
acc1[7] = vfmaq_f32(acc1[7], av, bv7);
let av = vld1q_f32(a2_base.add(ko));
acc2[0] = vfmaq_f32(acc2[0], av, bv0);
acc2[1] = vfmaq_f32(acc2[1], av, bv1);
acc2[2] = vfmaq_f32(acc2[2], av, bv2);
acc2[3] = vfmaq_f32(acc2[3], av, bv3);
acc2[4] = vfmaq_f32(acc2[4], av, bv4);
acc2[5] = vfmaq_f32(acc2[5], av, bv5);
acc2[6] = vfmaq_f32(acc2[6], av, bv6);
acc2[7] = vfmaq_f32(acc2[7], av, bv7);
let av = vld1q_f32(a3_base.add(ko));
acc3[0] = vfmaq_f32(acc3[0], av, bv0);
acc3[1] = vfmaq_f32(acc3[1], av, bv1);
acc3[2] = vfmaq_f32(acc3[2], av, bv2);
acc3[3] = vfmaq_f32(acc3[3], av, bv3);
acc3[4] = vfmaq_f32(acc3[4], av, bv4);
acc3[5] = vfmaq_f32(acc3[5], av, bv5);
acc3[6] = vfmaq_f32(acc3[6], av, bv6);
acc3[7] = vfmaq_f32(acc3[7], av, bv7);
}
// Horizontal reduction: sum each float32x4 accumulator to a scalar
// and add to C[i][j]. vaddvq_f32 sums all 4 lanes.
let c0 = c_ptr.add(i_start * n + j_start);
let c1 = c_ptr.add((i_start + 1) * n + j_start);
let c2 = c_ptr.add((i_start + 2) * n + j_start);
let c3 = c_ptr.add((i_start + 3) * n + j_start);
for jj in 0..TILE_J {
*c0.add(jj) += vaddvq_f32(acc0[jj]);
*c1.add(jj) += vaddvq_f32(acc1[jj]);
*c2.add(jj) += vaddvq_f32(acc2[jj]);
*c3.add(jj) += vaddvq_f32(acc3[jj]);
}
// Scalar remainder for k-values not covered by NEON loads
let k_scalar_start = k_start + (k_len / 4) * 4;
if k_scalar_start < k_end {
for ii in 0..TILE_I {
let i = i_start + ii;
for jj in 0..TILE_J {
let j = j_start + jj;
let mut sum = 0.0f32;
for p in k_scalar_start..k_end {
// SAFETY: i < m, p < k, j < n — within bounds.
sum += *a_ptr.add(i * k + p) * *b_ptr.add(j * k + p);
}
*c_ptr.add(i * n + j) += sum;
}
}
}
} else {
// Edge tiles: partial I or J count, or k_len < 8.
// Still use NEON for the dot product along k where possible.
for ii in 0..i_count {
let i = i_start + ii;
let a_base = a_ptr.add(i * k + k_start);
for jj in 0..j_count {
let j = j_start + jj;
let b_base = b_ptr.add(j * k + k_start);
let kl = k_end - k_start;
let mut acc = vdupq_n_f32(0.0);
let k_vec = kl / 4;
for kk in 0..k_vec {
let off = kk * 4;
let av = vld1q_f32(a_base.add(off));
let bv = vld1q_f32(b_base.add(off));
acc = vfmaq_f32(acc, av, bv);
}
let mut sum = vaddvq_f32(acc);
for p in (k_vec * 4)..kl {
sum += *a_base.add(p) * *b_base.add(p);
}
*c_ptr.add(i * n + j) += sum;
}
}
}
k_start += TILE_K;
}
i_start += TILE_I;
}
j_start += TILE_J;
}
}