Performance optimisation for parameters passed by value that are C++11 movable.

The C++ wrappers create a temporary variable for a parameter to be passed to a
function. This is initially default constructed and then copy assigned from the
instance being passed in from the target language. This is unchanged, however,
when the temporary variable is passed to wrapped function, it is now done using
std::move. If the type is move constructible, the move constructor will be used
instead of the copy constructor.

Note that the implementation calls std::move for all user-defined types
(non-primitive types passed by value), this excludes anything passed by pointer,
reference and arrays. It does also include any type that has not been
defined/parsed by SWIG, that is, unknown types. std::move is called via the
SWIG_STD_MOVE macro which only calls std::move for C++11 and later code.

CHANGES.current

@@ -7,8 +7,17 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.1.0 (in progress)
 ===========================
 
+2022-07-08: wsfulton
+            Performance optimisation for parameters passed by value that are C++11 movable.
+            The C++ wrappers create a temporary variable for a parameter to be passed to a
+            function. This is initially default constructed and then copy assigned from the
+            instance being passed in from the target language. This is unchanged, however,
+            when the temporary variable is passed to wrapped function, it is now done using
+            std::move. If the type is move constructible, the move constructor will be used
+            instead of the copy constructor.
+
 2022-07-03: wsfulton
-            Performane optimisation for directors for classes passed by value. The directorin
+            Performance optimisation for directors for classes passed by value. The directorin
             typemaps in the director methods now use std::move on the input parameter when
             copying the object from the stack to the heap prior to the callback into the target
             language, thereby taking advantage of move semantics if available.

Examples/test-suite/csharp/cpp11_move_only_runme.cs

@@ -27,8 +27,8 @@ public class cpp11_move_only_runme {
     using (MovableCopyable mo = new MovableCopyable(222)) {
       Counter.check_counts(1, 0, 0, 0, 0, 0);
       MovableCopyable.take(mo);
-      Counter.check_counts(2, 1, 1, 0, 0, 2);
+      Counter.check_counts(2, 0, 1, 1, 0, 2);
     }
-    Counter.check_counts(2, 1, 1, 0, 0, 3);
+    Counter.check_counts(2, 0, 1, 1, 0, 3);
   }
 }

Examples/test-suite/java/cpp11_move_only_runme.java

@@ -43,9 +43,9 @@ public class cpp11_move_only_runme {
       MovableCopyable mo = new MovableCopyable(222);
       Counter.check_counts(1, 0, 0, 0, 0, 0);
       MovableCopyable.take(mo);
-      Counter.check_counts(2, 1, 1, 0, 0, 2);
+      Counter.check_counts(2, 0, 1, 1, 0, 2);
       mo.delete();
-      Counter.check_counts(2, 1, 1, 0, 0, 3);
+      Counter.check_counts(2, 0, 1, 1, 0, 3);
     }
   }
 }

Examples/test-suite/python/cpp11_move_only_runme.py

@@ -22,6 +22,6 @@ Counter.reset_counts()
 mo = MovableCopyable(222)
 Counter.check_counts(1, 0, 0, 0, 0, 0)
 MovableCopyable.take(mo)
-Counter.check_counts(2, 1, 1, 0, 0, 2)
+Counter.check_counts(2, 0, 1, 1, 0, 2)
 del mo
-Counter.check_counts(2, 1, 1, 0, 0, 3)
+Counter.check_counts(2, 0, 1, 1, 0, 3)

Source/Swig/cwrap.c

@@ -427,10 +427,14 @@ String *Swig_cfunction_call(const_String_or_char_ptr name, ParmList *parms) {
       String *rcaststr = SwigType_rcaststr(rpt, pname);
 
       if (comma) {
-	Printv(func, ",", rcaststr, NIL);
-      } else {
-	Append(func, rcaststr);
+	Append(func, ",");
       }
+
+      if (cparse_cplusplus && SwigType_type(rpt) == T_USER)
+	Printv(func, "SWIG_STD_MOVE(", rcaststr, ")", NIL);
+      else
+	Printv(func, rcaststr, NIL);
+
       Delete(rpt);
       Delete(pname);
       Delete(rcaststr);