From 73af7c60a11d70ff0c992bc458d2c72d35b86dd4 Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Thu, 13 Jun 2024 02:51:52 +0800
Subject: [PATCH] nrvo for embedded importc'ed types (#23708)

(cherry picked from commit 0b5a938f571133f6e876938387e37199d4c2ec16)
---
 compiler/ccgtypes.nim | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/compiler/ccgtypes.nim b/compiler/ccgtypes.nim
index 4dc0e3ab71..5c3fdfaf75 100644
--- a/compiler/ccgtypes.nim
+++ b/compiler/ccgtypes.nim
@@ -273,9 +273,12 @@ proc isInvalidReturnType(conf: ConfigRef; typ: PType, isProc = true): bool =
       if rettype.isImportedCppType or t.isImportedCppType or
           (typ.callConv == ccCDecl and conf.selectedGC in {gcArc, gcAtomicArc, gcOrc}):
         # prevents nrvo for cdecl procs; # bug #23401
-        return false
-      result = containsGarbageCollectedRef(t) or
-          (t.kind == tyObject and not isObjLackingTypeField(t))
+        result = false
+      else:
+        result = containsGarbageCollectedRef(t) or
+            (t.kind == tyObject and not isObjLackingTypeField(t)) or
+            (getSize(conf, rettype) == szUnknownSize and (t.sym == nil or sfImportc notin t.sym.flags))
+
     else: result = false
 
 const