使用DirectXMath中的XMVECTOR作为类成员只会在释放模式下导致崩溃？

问题描述

我一直试图使用XMVECTOR作为边界框的类成员，因为我做了很多计算，但我每次使用XMFLOAT3只有一次，所以边界框有一个方法，它给我它的中心在XMFLOAT3中，否则它保留在XMVECTOR中;类使用__declspec（align（16））delcared并且在调试模式下工作。然而在发布模式下，它将崩溃的时间我设置为某物：

  Box& Box :: operator =（const Box& box）
 {
 _center = box._center; 
 _extents = box._extents; 
 return * this; 
} 
  

每当我这样做：

  Box A; 
 
 Box B; 
 
 A = B; 
  

它崩溃，给我0xC0000005：访问冲突读取位置0x00000000。
当我创建它作为一个指针时崩溃：

  Box * A = new Box 
  

这是构造函数：

  Box :: Box（）
 {
 center = XMVectorZero（）; 
 extents = XMVectorSplatOne（）; 
} 
  

同样，这在Debug模式下可以正常工作，

解决方案

类不是在对齐的地址创建的，所以即使XM *成员在16字节边界对齐，父对齐错误对齐他们，导致崩溃。

为了防止这种情况，你需要使用 _mm_alloc （这真的只是包装），或将默认分配器替换为返回最低限度对齐到16个字节的块（在x64下，使用默认分配器的情况下）。

在C ++中一个简单的解决方案是为所有类创建一个基类包含如下所示的XM *成员：

 模板< size_t Alignment> class AlignedAllocationPolicy 
 {
 public：
 static void * operator new（size_t size）
 {
 return _aligned_malloc（size，Alienment）; 
} 
 
 static void operator delete（void * memory）
 {
 _aligned_free（memory）; 
} 
}; 
 
 class MyAlignedObject：public AlignedAllocationPolicy< 16> 
 {
 // ... 
}; 
  

正如@Dave所指出的，这是一个最小的例子， > all new 和 delete 运算符，特别是 new [ code>和 delete []

I've been trying to use XMVECTOR as a class member for a bounding box, since I do a lot of calculations, but I use the XMFLOAT3 only once per frame, so the bounding box has a method that gives me it's center in a XMFLOAT3, otherwise it stays in a XMVECTOR;The class is delcared with __declspec(align(16)) and works in debug mode.However in Release mode it crashes the instant I set it to something:

    Box& Box::operator=(const Box& box)
    {
        _center = box._center;
        _extents = box._extents;
        return *this;
    }

Whenever I do:

Box A;

Box B;

A = B;

It crashes, giving me 0xC0000005: Access violation reading location 0x00000000.Also it crashes when I create it as a pointer:

Box* A = new Box();

This is the constructor:

    Box::Box()
    {
        center = XMVectorZero();
        extents = XMVectorSplatOne();
    }

Again, this works fine in Debug mode, but in Release it crashes.What could Release mode be changing that would generate invalid code?Do I need to do something else, other than aligning the box to 16 bytes?

解决方案

The class is not being created at an aligned address, so even though the XM* members are aligned on 16-byte boundaries, the parent's alignment miss-aligns them, causing the crash.

To prevent this you need to use _mm_alloc (which really just wraps _aligned_alloc), or replace the default allocator with one that returns blocks minimally aligned to 16 bytes (under x64 this the case with the default allocator).

a simple solution to this in C++ is to create a base class for all classes the contain XM* members that looks like the following:

template<size_t Alignment> class AlignedAllocationPolicy
{
    public:
    static void* operator new(size_t size)
    {
        return _aligned_malloc(size,Alienment);
    }

    static void operator delete(void* memory)
    {
        _aligned_free(memory);
    }
};

class MyAlignedObject : public AlignedAllocationPolicy<16>
{
//...
};

As pointed out by @Dave, this is a minimal example, you'd want to overload all the new and delete operators, specifically new[] and delete[]

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