Fix calling convention for struct

gen.c

@@ -959,15 +959,13 @@ static int emit_args(Vector *vals) {
     int r = 0;
     for (int i = 0; i < vec_len(vals); i++) {
         Node *v = vec_get(vals, i);
-        if (v->ty->kind == KIND_STRUCT) {
-            emit_addr(v);
+        emit_expr(v);
+        if (is_large_struct(v->ty)) {
             r += push_struct(v->ty->size);
         } else if (is_flotype(v->ty)) {
-            emit_expr(v);
             push_xmm(0);
             r += 8;
         } else {
-            emit_expr(v);
             push("rax");
             r += 8;
         }
@@ -1090,7 +1088,29 @@ static void emit_return(Node *node) {
     SAVE;
     if (node->retval) {
         emit_expr(node->retval);
-        maybe_booleanize_retval(node->retval->ty);
+        if (is_large_struct(node->retval->ty)) {
+            push("rcx");
+            push("r11");
+            int i = 0;
+            emit("movq -8(#rbp), #rcx");
+            for (; i < node->retval->ty->size; i += 8) {
+                emit("movq %d(#rax), #r11", i);
+                emit("movq #r11, %d(#rcx)", i);
+            }
+            for (; i < node->retval->ty->size; i += 4) {
+                emit("movq %d(#rax), #r11", i);
+                emit("movq #r11, %d(#rcx)", i);
+            }
+            for (; i < node->retval->ty->size; i++) {
+                emit("movq %d(#rax), #r11", i);
+                emit("movq #r11, %d(#rcx)", i);
+            }
+            emit("mov #rcx, #rax");
+            pop("r11");
+            pop("rcx");
+        } else {
+            maybe_booleanize_retval(node->retval->ty);
+        }
     }
     emit_ret();
 }

parse.c

@@ -795,9 +795,16 @@ static Node *read_alignof_operand() {
  * Function arguments
  */
 
-static Vector *read_func_args(Vector *params) {
+static Vector *read_func_args(Type *ty) {
+    Vector *params = ty->params;
     Vector *args = make_vector();
     int i = 0;
+    if (is_large_struct(ty->rettype)) {
+        Node *retval = ast_lvar(ty->rettype, make_tempname());
+        retval = ast_uop(AST_ADDR, make_ptr_type(ty->rettype), retval);
+        vec_push(args, retval);
+        i++;
+    }
     for (;;) {
         if (next_token(')')) break;
         Node *arg = conv(read_assignment_expr());
@@ -824,10 +831,10 @@ static Vector *read_func_args(Vector *params) {
 static Node *read_funcall(Node *fp) {
     if (fp->kind == AST_ADDR && fp->operand->kind == AST_FUNCDESG) {
         Node *desg = fp->operand;
-        Vector *args = read_func_args(desg->ty->params);
+        Vector *args = read_func_args(desg->ty);
         return ast_funcall(desg->ty, desg->fname, args);
     }
-    Vector *args = read_func_args(fp->ty->ptr->params);
+    Vector *args = read_func_args(fp->ty->ptr);
     return ast_funcptr_call(fp, args);
 }
 
@@ -2349,6 +2356,14 @@ static Node *read_funcdef() {
         read_oldstyle_param_type(params);
         functype->params = param_types(params);
     }
+    if (is_large_struct(functype->rettype)) {
+        Vector *new_params = make_vector();
+        vec_push(new_params,
+                 ast_lvar(make_ptr_type(functype->rettype), make_tempname()));
+        vec_append(new_params, params);
+        params = new_params;
+        functype->params = param_types(params);
+    }
     functype->isstatic = (sclass == S_STATIC);
     ast_gvar(functype, name);
     expect('{');

test/struct.c

@@ -322,6 +322,10 @@ struct abi_check {
     struct abi_check_nest z;
 };
 
+typedef struct abi_check_small {
+    int x;
+};
+
 static int struct_arg_func(struct abi_check s1, struct abi_check s2) {
   int r = s1.x + s1.y + s1.z.a + s1.z.b + s1.z.c;
   r -= s2.x + s2.y + s2.z.a + s2.z.b + s2.z.c;
@@ -361,6 +365,40 @@ static void struct_global(void) {
     expect(14, sn.c);
 }
 
+static struct abi_check return_struct_func(int x, int y, int a, int b, int c) {
+    struct abi_check s;
+    s.x = x;
+    s.y = y;
+    s.z.a = a;
+    s.z.b = b;
+    s.z.c = c;
+    return s;
+}
+
+static int sum_struct(int base, struct abi_check s) {
+    return base + s.x + s.y + s.z.a + s.z.b + s.z.c;
+}
+
+static void struct_return(void) {
+    struct abi_check s = return_struct_func(42, 43, 44, 45, 46);
+    expect(42, s.x);
+    expect(43, s.y);
+    expect(44, s.z.a);
+    expect(45, s.z.b);
+    expect(46, s.z.c);
+    expect(21, sum_struct(6, return_struct_func(1, 2, 3, 4, 5)));
+    expect(55, sum_struct(sum_struct(0, return_struct_func(1, 2, 3, 4, 5)),
+                          return_struct_func(6, 7, 8, 9, 10)));
+}
+
+static int struct_arg_func_small(int v, struct abi_check_small s) {
+    return v + s.x;
+}
+
+static void struct_call_small(void) {
+    expect(43, struct_arg_func_small(1, (struct abi_check_small){ 42 }));
+}
+
 void testmain() {
     print("struct");
     t1();
@@ -392,4 +430,6 @@ void testmain() {
     struct_call();
     struct_local();
     struct_global();
+    struct_return();
+    struct_call_small();
 }