Add verification to the HLSL test

tools/clang/test/CodeGenHLSL/SplatGroupSharedScalar.hlsl

@@ -1,4 +1,11 @@
-// RUN: %dxc -E main -T cs_6_0 %s
+// RUN: %dxc -E main -T cs_6_0 -fcgl %s | FileCheck %s
+
+// Validate that when swizzling requires an r-value (i.e. duplicate elements), that the result is stored to
+// and loaded from a temporary.
+// CHECK:      store <1 x i32> %splat.splat, <1 x i32>* %tmp
+// CHECK-NEXT: %1 = load <1 x i32>, <1 x i32>* %tmp
+// CHECK-NEXT: %2 = shufflevector <1 x i32> %1, <1 x i32> undef, <4 x i32> zeroinitializer
+// CHECK-NEXT: store <4 x i32> %2, <4 x i32>* %x
 
 groupshared int a;
 [numthreads(64, 1, 1)]