Added subgroup support for xnrm2.

Author: EJainDev

src/kernels/level1/xnrm2.opencl

@@ -14,6 +14,12 @@
 // literal). Comment-out this line for syntax-highlighting when developing.
 R"(
 
+#if defined(cl_khr_work_group_uniform_arithmetic)
+#pragma OPENCL EXTENSION cl_khr_work_group_uniform_arithmetic : enable
+#elif defined(cl_khr_subgroups)
+#pragma OPENCL EXTENSION cl_khr_subgroups : enable
+#endif
+
 // Parameters set by the tuner or by the database. Here they are given a basic default value in case
 // this kernel file is used outside of the CLBlast library.
 #ifndef WGS1
@@ -61,12 +67,22 @@ void Xnrm2(const int n,
       output[wgid] = result;
     }
   #else
-    for (int s=WGS1/2; s>0; s=s>>1) {
-      if (lid < s) {
-        Add(lm[lid], lm[lid], lm[lid + s]);
-      }
+    #if defined(cl_khr_subgroups) || defined(__opencl_c_subgroups)
+      lm[get_sub_group_local_id()] = sub_group_reduce_add(lm[lid]);
       barrier(CLK_LOCAL_MEM_FENCE);
-    }
+      for (int s = get_num_sub_groups() >> 1; s > 0; s >>= 1) {
+        if (lid < s) {
+          Add(lm[lid], lm[lid], lm[lid + s]);
+        }
+      }
+    #else
+      for (int s=WGS1/2; s>0; s=s>>1) {
+        if (lid < s) {
+          Add(lm[lid], lm[lid], lm[lid + s]);
+        }
+        barrier(CLK_LOCAL_MEM_FENCE);
+      }
+    #endif
 
     if (lid == 0) {
       output[wgid] = lm[0];
@@ -104,12 +120,22 @@ void Xnrm2Epilogue(const __global real* restrict input,
       #endif
     }
   #else
-    for (int s=WGS1/2; s>0; s=s>>1) {
-      if (lid < s) {
-        Add(lm[lid], lm[lid], lm[lid + s]);
-      }
+    #if defined(cl_khr_subgroups) || defined(__opencl_c_subgroups)
+      lm[get_sub_group_local_id()] = sub_group_reduce_add(lm[lid]);
       barrier(CLK_LOCAL_MEM_FENCE);
-    }
+      for (int s = get_num_sub_groups() >> 1; s > 0; s >>= 1) {
+        if (lid < s) {
+          Add(lm[lid], lm[lid], lm[lid + s]);
+        }
+      }
+    #else
+      for (int s=WGS1/2; s>0; s=s>>1) {
+        if (lid < s) {
+          Add(lm[lid], lm[lid], lm[lid + s]);
+        }
+        barrier(CLK_LOCAL_MEM_FENCE);
+      }
+    #endif
 
     if (lid == 0) {
       #if PRECISION == 3232 || PRECISION == 6464