[cfe-dev] Clang issue with __declspec(property)

[chen xu]

When using clang (3.6.0, on Ubuntu 15.04) to build a C++ class with __declspec(property), we observed a strange behavior, please see sample code below.
 
00  #include <stdio.h>
01  class Test1 {
02  private:
03      int x_;
04  public:
05      Test1(int x) : x_(x) {}
06      __declspec(property(get=get_x)) int X;
07      int get_x() const { return x_; }
08      static Test1* GetTest1() { printf("create, "); return new Test1(10); }
09  };
10  int main(int argc, char** argv) {
11      int x = Test1::GetTest1()->X;
12      printf("x=%d\n",x);
13  }
 
The execution output is like: 
create, create, x=10
 
Basically, the compiler builds the code line 11 into
0x000000000040077f  call 0x4007c0 <Test1::GetTest1()> 

0x0000000000400784  mov QWORD PTR [rbp-0x20],rax 

0x0000000000400788  call 0x4007c0 <Test1::GetTest1()> 

0x000000000040078d  mov rdi,rax 

0x0000000000400790  call 0x400830 <Test1::get_x() const> 

0x0000000000400795  movabs rdi,0x4008e4 

0x000000000040079f  mov DWORD PTR [rbp-0x14],eax 
 
As we notice, Test1::GetTest1() is called twice. The result of the 1st call is stored into a compiler-allocated stack variable, and seems never used later; The result of the 2nd call is passed as "this" pointer to Test1::get_x(). Is this an expected behavior? Since our real GetTest1() is not idempotent, being called twice is causing incorrect program behavior. Could any folk working on __declspec(property) feature of clang take a look? Thanks a lot in advance. 
 
 		 	   		  
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