[mlir] Modify linalg loops test to have nested regions

[nicolasvasilache]

Thanks!

mlir/test/Dialect/Linalg/loops.mlir

 ]
 #scalar_trait = {
   args_in = 2,
   args_out = 1,
   iterator_types = [],
   indexing_maps = #scalar_access,
   library_call = "some_external_fn"
 }
-func @scalar_code(%arg0: memref<f32>, %arg1 : memref<f32>, %arg2 : memref<f32>)
+func @scalar_code(%arg0: memref<f32>, %arg1 : memref<f32>, %arg2 : memref<f32>, %arg3 : i1)
 {
   linalg.generic #scalar_trait
     ins(%arg0, %arg1 : memref<f32>, memref<f32>)
    outs(%arg2 : memref<f32>) {
   ^bb(%a : f32, %b : f32, %c : f32) :
-    %0 = addf %a, %b : f32
-    linalg.yield %0 : f32
+    %result = scf.if %arg3 -> (f32) {
+      scf.yield %a : f32
+    } else {
+      scf.yield %b : f32
+    }
+    linalg.yield %result : f32
   }
   return
 }
 // CHECKLOOP-LABEL: @scalar_code
 //  CHECKLOOP-SAME: %[[ARG0:[a-zA-Z0-9_]*]]: memref<f32>
 //  CHECKLOOP-SAME: %[[ARG1:[a-zA-Z0-9_]*]]: memref<f32>
 //  CHECKLOOP-SAME: %[[ARG2:[a-zA-Z0-9_]*]]: memref<f32>
 //   CHECKLOOP-NOT: scf.for
 //       CHECKLOOP: load %[[ARG0]][]
 //       CHECKLOOP: load %[[ARG1]][]
-//       CHECKLOOP: addf
+//       CHECKLOOP: scf.if
+//       CHECKLOOP: scf.yield
+//       CHECKLOOP: else
+//       CHECKLOOP: scf.yield
 //       CHECKLOOP: store %{{.*}}, %[[ARG2]][]
 
 // CHECKPARALLEL-LABEL: @scalar_code
 //  CHECKPARALLEL-SAME: %[[ARG0:[a-zA-Z0-9_]*]]: memref<f32>
 //  CHECKPARALLEL-SAME: %[[ARG1:[a-zA-Z0-9_]*]]: memref<f32>
 //  CHECKPARALLEL-SAME: %[[ARG2:[a-zA-Z0-9_]*]]: memref<f32>
 //   CHECKPARALLEL-NOT: scf.for
 //       CHECKPARALLEL: load %[[ARG0]][]
 //       CHECKPARALLEL: load %[[ARG1]][]
-//       CHECKPARALLEL: addf
+//       CHECKPARALLEL: scf.if
+//       CHECKPARALLEL: scf.yield
+//       CHECKPARALLEL: else
+//       CHECKPARALLEL: scf.yield
 //       CHECKPARALLEL: store %{{.*}}, %[[ARG2]][]
 
 //----------------------------------------------------------------------------//
 // Named ops to loops.
 //----------------------------------------------------------------------------//
 func @named_batch_matmul(%A: memref<?x?x?xf32>, %B: memref<?x?x?xf32>, %C: memref<?x?x?xf32>) {
   linalg.batch_matmul ins(%A, %B : memref<?x?x?xf32>, memref<?x?x?xf32>)
                      outs(%C : memref<?x?x?xf32>)