--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang/test/CodeGenCXX/regparm.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,38 @@
+// RUN: %clang_cc1 -triple i386-unknown-unknown %s -emit-llvm -o - | FileCheck %s
+
+
+// CHECK: _Z3fooRi(i32* inreg
+void __attribute__ ((regparm (1)))  foo(int &a) {
+}
+
+struct S1 {
+  int x;
+  S1(const S1 &y);
+};
+
+void __attribute__((regparm(3))) foo2(S1 a, int b);
+// CHECK: declare void @_Z4foo22S1i(%struct.S1* inreg, i32 inreg)
+void bar2(S1 a, int b) {
+  foo2(a, b);
+}
+
+struct S2 {
+  int x;
+};
+
+void __attribute__((regparm(3))) foo3(struct S2 a, int b);
+// CHECK: declare void @_Z4foo32S2i(i32 inreg, i32 inreg)
+void bar3(struct S2 a, int b) {
+  foo3(a, b);
+}
+
+struct S3 {
+  struct {
+    struct {} b[0];
+  } a;
+};
+__attribute((regparm(2))) void foo4(S3 a, int b);
+// CHECK: declare void @_Z4foo42S3i(%struct.S3* byval(%struct.S3) align 4, i32 inreg)
+void bar3(S3 a, int b) {
+  foo4(a, b);
+}