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Re: SSE2(/AVX) and alignment issues [message #30971 is a reply to message #30968]

Sun, 30 January 2011 18:24

mirek
Messages: 13976
Registered: November 2005

Ultimate Member

tojocky wrote on Sun, 30 January 2011 10:52

Looking in boost code:

class X{
public:

    explicit X(int n): n_(n){
    }

    void * operator new(std::size_t){
        return std::allocator<X>().allocate(1, static_cast<X*>(0));
    }

    void operator delete(void * p){
        std::allocator<X>().deallocate(static_cast<X*>(p), 1);
    }

private:

    X(X const &);
    X & operator=(X const &);

    int n_;
};

class Y{
public:

    explicit Y(int n): n_(n){
    }

    void * operator new(std::size_t n){
        return boost::detail::quick_allocator<Y>::alloc(n);
    }

    void operator delete(void * p, std::size_t n){
        boost::detail::quick_allocator<Y>::dealloc(p, n);
    }

private:

    Y(Y const &);
    Y & operator=(Y const &);

    int n_;
};

where something in the memory alocator we can get alignmet of type by:

for Codegear: alignof(T)
for GCC: __alignof__(T)
for MSC: __alignof(T)

according by IBM link and boost source code.

According by boost source code in file intrinsics.hpp MSC __alignof(T) fails when used with /Zp property. We need to be care of.

In this case we can easily use sse2/3/4/...:

Y y_v = new Y(1);

Is possible to implement a tool that can be integrated in the "operator new" of the classes with sse2/3/4 types properties?

Sorry, if it is a stupid question. I have not experience with sse, but i'me very interested to speed up the program by using sse/2/3/4.

struct Foo {
   int bar;
   Y y;
};

and we are back where we were...

Anyway, deeper research has revealed that all this is somewhat obsolete. Where I am heading now is larger vectors of values that are fully encapsulated in some object (which can keep proper alignment) and using the most advanced ISA available... Smile

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