Managed C++/CLI

static MCppStruct GetStack()              | public static CshStruct GetNew()
{ return MCppStruct(1,2,3); }             | { return new CshStruct(1, 2, 3); }
-------------------------------------------------------------------------------------
00  push  ebp                             | 00  push  ebp
01  mov   ebp,esp                         | 01  mov   ebp,esp
03  sub   esp,10h                         | 03  sub   esp,10h
06  push  edi                             | 06  push  edi
07  push  esi                             | 07  push  esi
08  push  ebx                             | 08  push  ebx
09  <FONT color="green">mov   ebx,ecx</FONT>                         |  
0b  <FONT color=blue>lea   edi,[ebp-10h]</FONT>                   |  
0e  xor   eax,eax                         | 09  xor   eax,eax
10  <FONT color=blue>stos  dword ptr [edi]</FONT>                 | 0b  <FONT color=blue>mov   dword ptr [ebp-10h],eax</FONT>
11  <FONT color=blue>stos  dword ptr [edi]</FONT>                 | 0e  <FONT color=blue>mov   dword ptr [ebp-0Ch],eax</FONT>
12  <FONT color=blue>stos  dword ptr [edi]</FONT>                 | 11  <FONT color=blue>mov   dword ptr [ebp-8],eax</FONT>
                                          | 14  <FONT color="green">mov   ebx,ecx</FONT>
13  push  2                               | 16  push  2
15  push  3                               | 18  push  3
17  lea   ecx,[ebp-10h]                   | 1a  lea   ecx,[ebp-10h]
1a  mov   edx,1                           | 1d  mov   edx,1
1f  call  dword ptr ds:[00825230h]        | 22  call  dword ptr ds:[008151F0h]
25  mov   edi,ebx                         | 28  mov   edi,ebx
27  lea   esi,[ebp-10h]                   | 2a  lea   esi,[ebp-10h]
2a  movs  dword ptr [edi],dword ptr [esi] | 2d  movs  dword ptr [edi],dword ptr [esi]
2b  movs  dword ptr [edi],dword ptr [esi] | 2e  movs  dword ptr [edi],dword ptr [esi]
2c  movs  dword ptr [edi],dword ptr [esi] | 2f  movs  dword ptr [edi],dword ptr [esi]
2d  pop   ebx                             | 30  pop   ebx 
2e  pop   esi                             | 31  pop   esi 
2f  pop   edi                             | 32  pop   edi
30  mov   esp,ebp                         | 33  mov   esp,ebp 
32  pop   ebp                             | 35  pop   ebp
33  ret                                   | 36  ret
-------------------------------------------------------------------------------------

In response to your questions:

1) 
The C# version is creating the struct on the stack.  Turns out newobj 
instruction can be used to create value types on the stack.  I verified 
this from the CIL spec (http://msdn.microsoft.com/net/ecma/ , see the link 
for CLI Partition III , which documents the CIL instruction set), and by 
writing a small MC++ sample that successfully consumes a value type 
returned from C# in this manner.

2)
Our team has entered a suggestion to see if we can generate more efficient 
CIL for the sample you provided.

-- 
Andrew Brown, Visual C++ Team
This posting is provided AS IS with no warranties, and confers no rights.

#include "stdafx.h"

#using <mscorlib.dll>
#include <tchar.h>

using namespace System;

__nogc struct StdHello
{
	int nSomething;
};

__value struct MCHello
{
	StdHello member;
};

// This is the entry point for this application
int _tmain(void)
{
    // TODO: Please replace the sample code below with your own.
    Console::WriteLine(S"Hello World");

	MCHello hello;
	hello.member.nSomething = 2003227;

	Console::WriteLine(__box(hello.member.nSomething));

    return 0;
}