推力减少和重载运算符-(const float3&amp ;, const float3&)不会编译 [英] Thrust reduction and overloaded operator-(const float3&, const float3&) won't compile

问题描述

我重载了运算符，使vectorspace.cuh中的float3(和类似结构)上的向量空间为:

I overload operators to have a vector space over float3 (and similar structs) in vectorspace.cuh:

// Boilerplate vector space over data type Pt
#pragma once

#include <type_traits>


// float3
__device__ __host__ float3 operator+=(float3& a, const float3& b) {
    a.x += b.x; a.y += b.y; a.z += b.z;
    return a;
}

__device__ __host__ float3 operator*=(float3& a, const float b) {
    a.x *= b; a.y *= b; a.z *= b;
    return a;
}

// float4
__device__ __host__ float4 operator+=(float4& a, const float4& b) {
    a.x += b.x; a.y += b.y; a.z += b.z; a.w += b.w;
    return a;
}

__device__ __host__ float4 operator*=(float4& a, const float b) {
    a.x *= b; a.y *= b; a.z *= b; a.w *= b;
    return a;
}


// Generalize += and *= to +, -=, -, *, /= and /
template<typename Pt> __device__ __host__
typename std::enable_if<std::is_class<Pt>::value || std::is_enum<Pt>::value, Pt>::type
operator+(const Pt& a, const Pt& b) {
    auto sum = a;
    sum += b;
    return sum;
}

template<typename Pt> __device__ __host__
typename std::enable_if<std::is_class<Pt>::value || std::is_enum<Pt>::value, Pt>::type
operator-=(Pt& a, const Pt& b) {
    a += -1*b;
    return a;
}

template<typename Pt> __device__ __host__
typename std::enable_if<std::is_class<Pt>::value || std::is_enum<Pt>::value, Pt>::type
operator-(const Pt& a, const Pt& b) {
    auto diff = a;
    diff -= b;
    return diff;
}

template<typename Pt> __device__ __host__
typename std::enable_if<std::is_class<Pt>::value || std::is_enum<Pt>::value, Pt>::type
operator-(const Pt& a) {
    return -1*a;
}

template<typename Pt> __device__ __host__
typename std::enable_if<std::is_class<Pt>::value || std::is_enum<Pt>::value, Pt>::type
operator*(const Pt& a, const float b) {
    auto prod = a;
    prod *= b;
    return prod;
}

template<typename Pt> __device__ __host__
typename std::enable_if<std::is_class<Pt>::value || std::is_enum<Pt>::value, Pt>::type
operator*(const float b, const Pt& a) {
    auto prod = a;
    prod *= b;
    return prod;
}

template<typename Pt> __device__ __host__
typename std::enable_if<std::is_class<Pt>::value || std::is_enum<Pt>::value, Pt>::type
operator/=(Pt& a, const float b) {
    a *= 1./b;
    return a;
}

template<typename Pt> __device__ __host__
typename std::enable_if<std::is_class<Pt>::value || std::is_enum<Pt>::value, Pt>::type
operator/(const Pt& a, const float b) {
    auto quot = a;
    quot /= b;
    return quot;
}

这些重载中断了thrust::reduce的编译，这里是一个示例:

These overloads break compilation of thrust::reduce, here an example:

#include <thrust/reduce.h>
#include <thrust/execution_policy.h>

#include "vectorspace.cuh"


int main(int argc, char const *argv[]) {
    int n = 10;
    float3* d_arr;
    cudaMalloc(&d_arr, n*sizeof(float3));

    auto sum = thrust::reduce(thrust::device, d_arr, d_arr + n, float3 {0});

    return 0;
}

在Ubuntu 16.04上使用nvcc -std=c++11 -arch=sm_52会导致200多行编译器错误:

Using nvcc -std=c++11 -arch=sm_52 on Ubuntu 16.04 this results in 200+ lines of compiler errors:

$ nvcc -std=c++11 -arch=sm_52 sandbox/mean.cu 
sandbox/mean.cu(26): error: no operator "*" matches these operands
            operand types are: int * const thrust::zip_iterator<thrust::tuple<const float3 *, thrust::pointer<float3, thrust::system::cuda::detail::par_t, thrust::use_default, thrust::use_default>, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type>>
          detected during:
            instantiation of "std::enable_if<<expression>, Pt>::type operator-=(Pt &, const Pt &) [with Pt=thrust::zip_iterator<thrust::tuple<const float3 *, thrust::pointer<float3, thrust::system::cuda::detail::par_t, thrust::use_default, thrust::use_default>, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type>>]" 
(35): here
            instantiation of "std::enable_if<<expression>, Pt>::type operator-(const Pt &, const Pt &) [with Pt=thrust::zip_iterator<thrust::tuple<const float3 *, thrust::pointer<float3, thrust::system::cuda::detail::par_t, thrust::use_default, thrust::use_default>, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type>>]" 

...

如何在不破坏thrust的情况下使运算符超载?

How can I overload the operators without breaking thrust?

推荐答案

^{_{(在OP编辑后编辑.)}}

问题出在运算符重载的到达"上:您不仅要为您感兴趣的类重载，而且要为符合您的enable_if条件的 all 类重载-相当放松.即使可以编译，这已经是一个严重的错误.

The problem is with the 'reach' of your operator overloads: You are not overloading only for the classes you're interested in, but for all classes fitting your enable_if condition - which is quite relaxed. That's already a serious bug even if things would compile.

更具体地说，推力使用算术运算，例如可以理解，在"zip迭代器"上(不管它们是什么)，您的操作编译失败.

More specifically, thrust uses arithmetic operations, e.g. on "zip iterators" (never mind what they are), and compilations of your operations for such iterators fails, understandably.

因此您必须:

• 准确指定过载与哪些类相关(例如，在enable_if中使用std::is_same的析取)，或

• 使用特征类:

• Specify exactly which classes the overload is relevant to (e.g., using a disjunction of std::is_same in the enable_if), or

• use a trait class:

template<class T> struct needs_qivs_arithmetic_operators : public std::false_type {};

template<> struct needs_qivs_arithmetic_operators<float3> : public std::true_type {};
template<> struct needs_qivs_arithmetic_operators<float4> : public std::true_type {};
/* ... etc. You can also add specializations elsewhere in the translation unit. */

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