SIMD和动态内存分配 [英] SIMD and dynamic memory allocation

问题描述

可能重复:
SSE，内在函数和对齐方式

我是SIMD编程的新手，所以请问一个明显的问题.

I'm new to SIMD programming, so please excuse me if I'm asking an obvious question.

我做了一些实验，以至于想要将SIMD值存储在动态分配的结构中.

I was experimenting a bit and got to a point where I want to store a SIMD value in a dynamically allocated structure.

代码如下:

struct SimdTest
{
    __m128      m_simdVal;

    void setZero()
    {
        __m128 tmp = _mm_setzero_ps(); 
        m_simdVal = tmp; // <<--- CRASH ---
    }
};

TEST( Plane, dynamicallyAllocatedPlane )
{
    SimdTest* test = new SimdTest();

    test->setZero();

    delete test;
}

执行标有CRASH注释的方法时，代码将崩溃，并具有以下异常:

When the method marked with CRASH comment is executed, the code crashes with the following exception:

Unhandled exception at 0x775315de in test-core.exe: 0xC0000005: Access violation reading location 0x00000000

有人可以解释一下为什么分配操作会中断，以及应该如何动态分配包含SIMD的对象以使其正常工作?

Could someone please explain why does the assignment operation break, and how should SIMD-containing objects be allocated dynamically so that they work fine?

我需要补充的是，如果我静态实例化SimdTest对象并调用setZero方法，则一切正常.

I need to add that if I statically instantiate a SimdTest object and call the setZero method, everything works fine.

谢谢，帕克萨斯(Paksas)

Thanks, Paksas

推荐答案

之所以死亡，是因为结构未对齐.CRT分配器仅承诺此处需要对齐8、16.您需要在MSVC上使用_aligned_malloc()以获得正确对齐的堆分配内存.

It dies because the structure is mis-aligned. The CRT allocator only promises alignment to 8, 16 is required here. You'll need to use _aligned_malloc() on MSVC to get properly aligned heap allocated memory.

两种解决方法.由于这是一个POD结构，因此您可以进行以下转换:

Two ways to go about it. Since this is a POD struct, you could just cast:

#include <malloc.h>
...
    SimdTest* test = (SimdTest*)_aligned_malloc(sizeof SimdTest, 16);
    test->setZero();
    _aligned_free(test);

或者您可以覆盖该结构的new/delete运算符:

Or you could override the new/delete operators for the struct:

struct SimdTest
{
    void* operator new(size_t size) { return _aligned_malloc(size, 16); }
    void operator delete(void* mem) { return _aligned_free(mem); }
    // etc..
};

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