SIMD AOT 10-20x slower. #63217

import 'dart:typed_data';

const int words = 2048;
const int iters = 200000;

void main() {
  print('words=$words (${words * 32} bits)  iters=$iters');
  final orS = bench('or      scalar', orScalar);
  final orV = bench('or      simd  ', orSimd);
  print('  -> simd/scalar = ${(orV / orS).toStringAsFixed(2)}x\n');
  final anS = bench('and_not scalar', andNotScalar);
  final anV = bench('and_not simd  ', andNotSimd);
  print('  -> simd/scalar = ${(anV / anS).toStringAsFixed(2)}x');
}

double bench(String label, void Function(Uint32List, Uint32List) op) {
  final a = Uint32List(words);
  final b = Uint32List(words);
  for (int i = 0; i < words; i++) {
    a[i] = 0xA5A5A5A5 ^ i;
    b[i] = 0x5A5A5A5A ^ (i * 31);
  }
  for (int w = 0; w < 50; w++) op(a, b); // warmup
  final sw = Stopwatch()..start();
  for (int k = 0; k < iters; k++) op(a, b);
  sw.stop();
  int sink = 0;
  for (int i = 0; i < words; i++) sink ^= a[i]; // prevent DCE
  final usPerIter = sw.elapsedMicroseconds / iters;
  print('$label: ${usPerIter.toStringAsFixed(3)} us/iter  (sink=$sink)');
  return usPerIter;
}

void orSimd(Uint32List a, Uint32List b) {
  final la = Int32x4List.view(a.buffer, a.offsetInBytes, a.length >> 2);
  final lb = Int32x4List.view(b.buffer, b.offsetInBytes, b.length >> 2);
  for (int j = 0; j < la.length; j++) {
    la[j] = la[j] | lb[j];
  }
}

void orScalar(Uint32List a, Uint32List b) {
  int i = 0;
  final n = a.length;
  for (; i + 7 < n; i += 8) {
    a[i] |= b[i];
    a[i + 1] |= b[i + 1];
    a[i + 2] |= b[i + 2];
    a[i + 3] |= b[i + 3];
    a[i + 4] |= b[i + 4];
    a[i + 5] |= b[i + 5];
    a[i + 6] |= b[i + 6];
    a[i + 7] |= b[i + 7];
  }
  for (; i < n; i++) a[i] |= b[i];
}

void andNotSimd(Uint32List a, Uint32List b) {
  // Int32x4 has no bitwise NOT, so use the identity a & ~b == a ^ (a & b).
  final la = Int32x4List.view(a.buffer, a.offsetInBytes, a.length >> 2);
  final lb = Int32x4List.view(b.buffer, b.offsetInBytes, b.length >> 2);
  for (int j = 0; j < la.length; j++) {
    final x = la[j];
    la[j] = x ^ (x & lb[j]);
  }
}

void andNotScalar(Uint32List a, Uint32List b) {
  int i = 0;
  final n = a.length;
  for (; i + 7 < n; i += 8) {
    a[i] &= ~b[i];
    a[i + 1] &= ~b[i + 1];
    a[i + 2] &= ~b[i + 2];
    a[i + 3] &= ~b[i + 3];
    a[i + 4] &= ~b[i + 4];
    a[i + 5] &= ~b[i + 5];
    a[i + 6] &= ~b[i + 6];
    a[i + 7] &= ~b[i + 7];
  }
  for (; i < n; i++) a[i] &= ~b[i];
}