[ROCm] deserialize loads in planer sum portion of stats() of norm

Cherry-pick of #2743

Co-authored-by: Jerry Mannil <[email protected]>

Author: rocm-repo-management-api[bot]

aten/src/ATen/native/cuda/Normalization.cuh

@@ -306,13 +306,30 @@ __global__ void batch_norm_collect_statistics_kernel(
   stat_accscalar_t var_n = 0;
   int n = 0;
   for (int batch = threadIdx.y; batch < input.size(0); batch += blockDim.y) {
+#if defined(USE_ROCM)
+    constexpr int UNRL = 4;
+    stat_accscalar_t v_[UNRL];
+    for (int x = threadIdx.x; x < input.size(2); x += blockDim.x*UNRL) {
+      for (int u = 0; u < UNRL; u++)
+        v_[u] = input[batch][plane][min(x+u*blockDim.x, input.size(2)-1)];
+      for (int u = 0; u < UNRL; u++) {
+        if (x+u*blockDim.x < input.size(2)) {
+          stat_accscalar_t d1 = v_[u] - avg;
+          n++;
+          avg += d1 / n;
+          var_n += d1 * (v_[u] - avg);
+        }
+      }
+    }
+#else
     for (int x = threadIdx.x; x < input.size(2); x += blockDim.x) {
       stat_accscalar_t v = input[batch][plane][x];
       stat_accscalar_t d1 = v - avg;
       n++;
       avg += d1 / n;
       var_n += d1 * (v - avg);
     }
+#endif
   }
 
   // first warpSum to get one value per thread to