From 167f5386432606d0a39ac27da15308eb64408284 Mon Sep 17 00:00:00 2001
From: tyfkda <tyfkda@gmail.com>
Date: Mon, 23 Oct 2023 10:34:03 +0900
Subject: [PATCH] Raise warning when return with void value

---
 src/cc/backend/codegen.c |  2 +-
 src/cc/frontend/parser.c | 12 +++++++++---
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/cc/backend/codegen.c b/src/cc/backend/codegen.c
index 98fe38652..bb8e7b85b 100644
--- a/src/cc/backend/codegen.c
+++ b/src/cc/backend/codegen.c
@@ -340,7 +340,7 @@ static void gen_return(Stmt *stmt) {
     if (is_prim_type(val->type)) {
       int flag = is_unsigned(val->type) ? IRF_UNSIGNED : 0;
       new_ir_result(fnbe->result_dst, vreg, flag);
-    } else {
+    } else if (val->type->kind != TY_VOID) {
       VReg *retval = fnbe->retval;
       if (retval != NULL) {
         gen_memcpy(val->type, retval, vreg);
diff --git a/src/cc/frontend/parser.c b/src/cc/frontend/parser.c
index 05b48775e..16d629120 100644
--- a/src/cc/frontend/parser.c
+++ b/src/cc/frontend/parser.c
@@ -443,10 +443,16 @@ static Stmt *parse_return(const Token *tok) {
     if (rettype->kind != TY_VOID)
       parse_error(PE_NOFATAL, tok, "`return' required a value");
   } else {
-    if (rettype->kind == TY_VOID)
-      parse_error(PE_NOFATAL, val->token, "void function `return' a value");
-    else
+    if (rettype->kind == TY_VOID) {
+      if (val->type->kind == TY_VOID) {
+        // Allow `return void_fnc();`.
+        parse_error(PE_WARNING, val->token, "`return' with void value");
+      } else {
+        parse_error(PE_NOFATAL, val->token, "void function `return' a value");
+      }
+    } else {
       val = make_cast(rettype, val->token, val, false);
+    }
   }
 
   return new_stmt_return(tok, val);