[LLVMbugs] [Bug 24132] New: __declspec(property): double invocations of foo() when compiling foo()->propertyName

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=24132

            Bug ID: 24132
           Summary: __declspec(property): double invocations of foo() when
                    compiling foo()->propertyName
           Product: clang
           Version: 3.6
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: chenxuz at outlook.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Code for repro is as follows. 

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.

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