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

[chen xu]

Thanks, Reid, David. I have submitted a PR at llvm bugzilla. https://llvm.org/bugs/show_bug.cgi?id=24132
Date: Tue, 14 Jul 2015 16:49:28 -0700
Subject: Re: [cfe-dev] Clang issue with __declspec(property)
From: rnk at google.com
To: chenxuz at outlook.com; majnemer at google.com
CC: cfe-dev at cs.uiuc.edu

David took a look at this. If you could file a PR for it, that'd be great.
On Thu, Jul 9, 2015 at 9:38 AM, chen xu <chenxuz at outlook.com> wrote:



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. 
 
 		 	   		  

_______________________________________________

cfe-dev mailing list

cfe-dev at cs.uiuc.edu

http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev



 		 	   		  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20150715/978f0741/attachment.html>