VSCALE microkernel and SoftMax Three-Pass algorithm with Reloading

- VSCALE micro-kernel in AVX and AVX512F implementations
- Unit tests
- Micro-benchmark for SoftArgMax using Three-Pass algorithm with Reloading

PiperOrigin-RevId: 275939577
diff --git a/bench/f32-softargmax.cc b/bench/f32-softargmax.cc
index 2ca1373..ad73f57 100644
--- a/bench/f32-softargmax.cc
+++ b/bench/f32-softargmax.cc
@@ -11,6 +11,7 @@
 #include <xnnpack/raddexpminusmax.h>
 #include <xnnpack/raddstoreexpminusmax.h>
 #include <xnnpack/rmax.h>
+#include <xnnpack/vscale.h>
 #include <xnnpack/vscaleexpminusmax.h>
 
 #include <benchmark/benchmark.h>
@@ -63,6 +64,53 @@
   state.SetBytesProcessed(uint64_t(state.iterations()) * 2 * sizeof(float) * n);
 }
 
+static void ThreePassSoftargmaxWithReloading(
+  benchmark::State& state,
+  xnn_f32_rmax_ukernel_function rmax,
+  xnn_f32_raddstoreexpminusmax_ukernel_function raddstoreexpminusmax,
+  xnn_f32_vscale_ukernel_function vscale)
+{
+  const size_t n = state.range(0);
+  const size_t cache_line_size_max = 128;
+  const size_t packed_n = benchmark::utils::roundUp(n, cache_line_size_max / sizeof(float));
+
+  std::random_device random_device;
+  auto rng = std::mt19937(random_device());
+  auto f32rng = std::bind(std::uniform_real_distribution<float>(-1000.0f, 1000.0f), rng);
+
+  const size_t num_buffers = 1 +
+    benchmark::utils::divideRoundUp<size_t>(benchmark::utils::GetMaxCacheSize(), packed_n * sizeof(float));
+  std::vector<float> x(n);
+  std::vector<float> y(packed_n * num_buffers);
+
+  std::generate(x.begin(), x.end(), std::ref(f32rng));
+
+  benchmark::utils::DisableDenormals();
+
+  size_t buffer_index = 0;
+  for (auto _ : state) {
+    benchmark::utils::prefetchToL1(x.data(), x.size() * sizeof(float));
+    if (++buffer_index == num_buffers) {
+      buffer_index = 0;
+    }
+
+    const auto start = std::chrono::high_resolution_clock::now();
+    float x_max = nanf("");
+    rmax(n * sizeof(float), x.data(), &x_max);
+    float y_sum = nanf("");
+    raddstoreexpminusmax(n * sizeof(float), x.data(), y.data() + packed_n * buffer_index, &y_sum, x_max);
+    vscale(n * sizeof(float), y.data() + packed_n * buffer_index, y.data() + packed_n * buffer_index, 1.0f / y_sum);
+    const auto end = std::chrono::high_resolution_clock::now();
+
+    const auto elapsed_seconds =
+      std::chrono::duration_cast<std::chrono::duration<double>>(end - start);
+    state.SetIterationTime(elapsed_seconds.count());
+  }
+
+  state.SetItemsProcessed(uint64_t(state.iterations()) * n);
+  state.SetBytesProcessed(uint64_t(state.iterations()) * 2 * sizeof(float) * n);
+}
+
 static void CharacteristicArguments(benchmark::internal::Benchmark* b) {
   for (int32_t n = 1000; n <= 10000000; n *= 10) {
     b->Arg(n);
@@ -74,10 +122,16 @@
   BENCHMARK_CAPTURE(ThreePassSoftargmaxWithRecomputing, avx512f_p5_scalef_unroll128,
     xnn_f32_rmax_ukernel__avx512f, xnn_f32_raddexpminusmax_ukernel__avx512f_p5_scalef_unroll128, xnn_f32_vscaleexpminusmax_ukernel__avx512f_p5_scalef_unroll128)
       ->Apply(CharacteristicArguments)->UseManualTime();
+  BENCHMARK_CAPTURE(ThreePassSoftargmaxWithReloading, avx512f_p5_scalef_unroll128,
+    xnn_f32_rmax_ukernel__avx512f, xnn_f32_raddstoreexpminusmax_ukernel__avx512f_p5_scalef_unroll128, xnn_f32_vscale_ukernel__avx512f_unroll64)
+      ->Apply(CharacteristicArguments)->UseManualTime();
 
   BENCHMARK_CAPTURE(ThreePassSoftargmaxWithRecomputing, avx2_p5_unroll64,
     xnn_f32_rmax_ukernel__avx, xnn_f32_raddexpminusmax_ukernel__avx2_p5_unroll64, xnn_f32_vscaleexpminusmax_ukernel__avx2_p5_unroll64)
       ->Apply(CharacteristicArguments)->UseManualTime();
+  BENCHMARK_CAPTURE(ThreePassSoftargmaxWithReloading, avx2_p5_unroll64,
+    xnn_f32_rmax_ukernel__avx, xnn_f32_raddstoreexpminusmax_ukernel__avx2_p5_unroll64, xnn_f32_vscale_ukernel__avx_unroll32)
+      ->Apply(CharacteristicArguments)->UseManualTime();
 #endif  // XNN_ARCH_X86 || XNN_ARCH_X86_64
 
 #ifndef XNNPACK_BENCHMARK_NO_MAIN