[mlir][ArmSME] Use vector.reduction add in zero test

[c-rhodes]

Summary

The inner 1d vector row can be summed with vector.reduction op. The
earlier mul reduction can't be updated similarly as it currently crashes
in the backend with:

LLVM ERROR: Expanding reductions for scalable vectors is undefined.

[awarzynski]

LGTM, ta!

The earlier mul reduction can't be updated similarly as it currently crashes
in the backend with:

LLVM ERROR: Expanding reductions for scalable vectors is undefined.

We should probably report this somewhere.

mlir/test/Integration/Dialect/Vector/CPU/ArmSME/vector-ops.mlir

func.func @entry() -> i32 {
   //     str za[vnum], [ptr]
   //     ...
   //
   %cst_0 = arith.constant dense<0> : vector<[16]x[16]xi8>
   vector.transfer_write %cst_0, %za_b[%c0, %c0] {in_bounds = [true, true]} : vector<[16]x[16]xi8>, memref<?x?xi8>
 
   // Verify memory is zeroed by doing an add reduction with initial value of
   // zero.
-  %init_0 = arith.constant 0 : i64
-  %add_reduce = scf.for %vnum = %c0 to %svl_b step %c1_index iter_args(%iter = %init_0) -> (i64) {
+  %init_0 = arith.constant 0 : i8
+  %add_reduce = scf.for %vnum = %c0 to %svl_b step %c1_index iter_args(%iter = %init_0) -> (i8) {
     %row = vector.load %za_b[%vnum, %c0] : memref<?x?xi8>, vector<[16]xi8>
-
-    %inner_add_reduce = scf.for %offset = %c0 to %svl_b step %c1_index iter_args(%inner_iter = %init_0) -> (i64) {
-      %t = vector.extractelement %row[%offset : index] : vector<[16]xi8>
-      %t_i64 = arith.extui %t : i8 to i64
-      %inner_add_reduce_next = arith.addi %inner_iter, %t_i64 : i64
-      scf.yield %inner_add_reduce_next : i64
-    }
-
-    %add_reduce_next = arith.addi %iter, %inner_add_reduce : i64
-    scf.yield %add_reduce_next : i64
+    %row_sum = vector.reduction <add>, %row : vector<[16]xi8> into i8
+    %add_reduce_next = arith.addi %iter, %row_sum : i8
+    scf.yield %add_reduce_next : i8
   }
 
   // CHECK-NEXT: 0
-  vector.print %add_reduce : i64
+  vector.print %add_reduce : i8
 
   // Verify the add reduction works as expected.
   //
   // TODO: ZA currently isn't re-enabled after calls and is therefore disable
   // by the callee on return. Once this is resolved this can be moved to a
   // function.
   memref.store %c4, %za_b[%c3, %c7] : memref<?x?xi8>
   memref.store %c15, %za_b[%c7, %c3] : memref<?x?xi8>
-  %add_reduce2 = scf.for %vnum = %c0 to %svl_b step %c1_index iter_args(%iter = %init_0) -> (i64) {
+  %add_reduce2 = scf.for %vnum = %c0 to %svl_b step %c1_index iter_args(%iter = %init_0) -> (i8) {
     %row = vector.load %za_b[%vnum, %c0] : memref<?x?xi8>, vector<[16]xi8>
-
-    %inner_add_reduce = scf.for %offset = %c0 to %svl_b step %c1_index iter_args(%inner_iter = %init_0) -> (i64) {
-      %t = vector.extractelement %row[%offset : index] : vector<[16]xi8>
-      %t_i64 = arith.extui %t : i8 to i64
-      %inner_add_reduce_next = arith.addi %inner_iter, %t_i64 : i64
-      scf.yield %inner_add_reduce_next : i64
-    }
-
-    %add_reduce_next = arith.addi %iter, %inner_add_reduce : i64
-    scf.yield %add_reduce_next : i64
+    %row_sum = vector.reduction <add>, %row : vector<[16]xi8> into i8
+    %add_reduce_next = arith.addi %iter, %row_sum : i8
+    scf.yield %add_reduce_next : i8
   }
 
   // 15+4=19
   // CHECK-NEXT: 19
-  vector.print %add_reduce2 : i64
+  vector.print %add_reduce2 : i8
 
   %c0_i32 = arith.constant 0 : i32
   return %c0_i32 : i32
 }