[ROCm] Deserialize loads in planer sum portion of reduce() of norm

Cherry-pick of #2740

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

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

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

@@ -115,9 +115,23 @@ __device__ scalar_t reduce(Op op, PTA tensor, int plane) {
   // first the reductions each thread does separately
   scalar_t sum = static_cast<scalar_t>(0);
   for (int batch = threadIdx.y; batch < tensor.size(0); batch += blockDim.y) {
+#if defined(USE_ROCM)
+    constexpr int UNRL = 4; // load deserilize factor
+    scalar_t tmp[UNRL];
+    for (int x = threadIdx.x; x < tensor.size(2); x += blockDim.x*UNRL) {
+#pragma unroll
+      for (int u = 0; u < UNRL; u++)
+        tmp[u] = op(batch, plane, min((int)tensor.size(2)-1, (int)(x+u*blockDim.x)));
+#pragma unroll
+      for (int u = 0; u < UNRL; u++)
+        if (x+u*blockDim.x < tensor.size(2))
+          sum += tmp[u];
+    }
+#else
     for (int x = threadIdx.x; x < tensor.size(2); x += blockDim.x) {
       sum += op(batch, plane, x);
     }
+#endif
   }
   __shared__ scalar_t shared[C10_WARP_SIZE];
   SumReduceOp<scalar_t> reduce_op;