why Visual Studio can not optimize the initialization code?

This is a discussion on why Visual Studio can not optimize the initialization code? within the C++ Programming forums, part of the General Programming Boards category; Hello everyone, Why Visual Studio compiler can not optimize in this case? I think this case is almost the same ...

  1. #1
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    why Visual Studio can not optimize the initialization code?

    Hello everyone,


    Why Visual Studio compiler can not optimize in this case? I think this case is almost the same as sample 1, why compiler can optimize sample 1 but can not optimze sample 2?

    (sample 2, http://msdn2.microsoft.com/en-us/lib...57(vs.80).aspx)

    Code:
    #include <stdio.h>
    class A {
      public:
        A() {printf ("A: I am in constructor\n");i = 1;}
        ~A() { printf ("A: I am in destructor\n"); i = 0;}
        A(const A& a) {printf ("A: I am in copy constructor\n"); i = a.i;}
        int i, x, w;
    };
     class B {
      public:
        A a;
        B()  { printf ("B: I am in constructor\n");}
        ~B() { printf ("B: I am in destructor\n");}
        B(const B& b) { printf ("B: I am in copy constructor\n");}
    };
    A MyMethod()
    {
        B* b = new B();
        A a = b->a;
        delete b;
        return (a);
    }
    int main()
    {
        A a;
        a = MyMethod();
    }

    thanks in advance,
    George

  2. #2
    The larch
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    Have you turned compiler optimizations on? Apparently VC++ 2005 won't use NRVO (here) if optimizations are off.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  3. #3
    and the hat of wrongness Salem's Avatar
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    AFAIK, a lot of the optimisations are disabled in the express (ie free) version.
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  4. #4
    C++ Witch laserlight's Avatar
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    AFAIK, a lot of the optimisations are disabled in the express (ie free) version.
    Didn't Microsoft tout the express version as having the optimising compiler?
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  5. #5
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    Quote Originally Posted by laserlight View Post
    Didn't Microsoft tout the express version as having the optimising compiler?
    I'm pretty sure it's the same compiler. I have no idea what the answer is to the above question, but I'm pretty sure that it's likely to be "interpreting the linked page", rather than what is supported and not by the compiler. Also, different versions of compilers may be more or less good at certain optimizations, and a newer compiler may have a bug-fix that an older one didn't have, which also means that some cases of certain optimizations are not done [because under some circumstances, the optimisation is unsafe].

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  6. #6
    The larch
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    I used the free VC++ 2005 compiler with Code::Blocks and I could produce both the optimized and non-optimized output by changing project settings.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  7. #7
    Algorithm Dissector iMalc's Avatar
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    Quote Originally Posted by laserlight View Post
    Didn't Microsoft tout the express version as having the optimising compiler?
    Yes VS2005 Express comes with the full optimising compiler.
    Otherwise my programs wouldn't be able to match or exceed the speed they ran at when compiled with an older full version MS compiler, with all optimisations on
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