[NFC] Add additional checks to test for vec_pack_to_short_fp32 (#130324)

Update test in prep for IR changes that will be introduced in
#129923

Author: lei137

clang/test/CodeGen/PowerPC/builtins-ppc-p9vector.c

@@ -853,10 +853,16 @@ vector unsigned char test73(void) {
 vector unsigned short test74(void) {
 // CHECK-BE: @llvm.ppc.vsx.xvcvsphp(<4 x float>
 // CHECK-BE: @llvm.ppc.vsx.xvcvsphp(<4 x float>
-// CHECK-BE: @llvm.ppc.altivec.vperm
+// CHECK-BE: [[REG0:%[0-9]+]] = call <4 x i32> @llvm.ppc.altivec.vperm
+// CHECK-BE-NEXT: [[REG1:%[0-9]+]] = bitcast <4 x i32> [[REG0]] to <4 x float>
+// CHECK-BE-NEXT: [[REG2:%[0-9]+]] = bitcast <4 x float> [[REG1]] to <8 x i16>
+// CHECK-BE-NEXT: ret <8 x i16> [[REG2]]
 // CHECK: @llvm.ppc.vsx.xvcvsphp(<4 x float>
 // CHECK: @llvm.ppc.vsx.xvcvsphp(<4 x float>
-// CHECK: @llvm.ppc.altivec.vperm
+// CHECK: [[REG0:%[0-9]+]] = call <4 x i32> @llvm.ppc.altivec.vperm
+// CHECK-NEXT: [[REG1:%[0-9]+]] = bitcast <4 x i32> [[REG0]] to <4 x float>
+// CHECK-NEXT: [[REG2:%[0-9]+]] = bitcast <4 x float> [[REG1]] to <8 x i16>
+// CHECK-NEXT: ret <8 x i16> [[REG2]]
   return vec_pack_to_short_fp32(vfa, vfb);
 }
 vector unsigned int test75(void) {