[X86] Add additional add of mul test (NFC)

Author: nikic

llvm/test/CodeGen/X86/add-of-mul.ll

@@ -13,6 +13,18 @@ define i32 @test_scalar(i32 %x) {
   ret i32 %add
 }
 
+define i32 @test_scalar_commuted(i32 %x) {
+; CHECK-LABEL: test_scalar_commuted:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    # kill: def $edi killed $edi def $rdi
+; CHECK-NEXT:    leal (%rdi,%rdi,2), %eax
+; CHECK-NEXT:    addl %edi, %eax
+; CHECK-NEXT:    retq
+  %mul = mul i32 %x, 3
+  %add = add i32 %x, %mul
+  ret i32 %add
+}
+
 define <4 x i32> @test_vector(<4 x i32> %x) {
 ; CHECK-LABEL: test_vector:
 ; CHECK:       # %bb.0: