C++：混淆可变参数模板导致“候选函数不可行”错误答案

【问题标题】：C++: confusing variadic template causing "candidate function not viable" errorC++：混淆可变参数模板导致“候选函数不可行”错误
【发布时间】：2019-08-19 17:23:21
【问题描述】：

我试图将 CUDA 项目移植到广泛使用 C++ 模板的 ROCm 平台。在此过程中，我收到以下编译错误

/root/warp-ctc/include/detail/gpu_ctc.h:381:5: error: no matching function for call to 'hipLaunchKernelGGL'
    hipLaunchKernelGGL((prepare_stable_SM_kernel<ProbT, VT>), dim3(grid_size), dim3(NT), 0, stream_, ctc_helper::identity<ProbT>(), probs_,
    ^~~~~~~~~~~~~~~~~~
.....
.....
/opt/rocm/hip/include/hip/hcc_detail/functional_grid_launch.hpp:138:13: note: candidate function [with Args = <ctc_helper::identity<float, float>, float *,
      float *, int, int>, F = void (*)(ctc_helper::identity<float, float>, float *, float *, int, int)] not viable: no overload of 'prepare_stable_SM_kernel'
      matching 'void (*)(ctc_helper::identity<float, float>, float *, float *, int, int)' for 1st argument
inline void hipLaunchKernelGGL(F kernel, const dim3& numBlocks, const dim3& dimBlocks,

为following piece of C++ code

hipLaunchKernelGGL((prepare_stable_SM_kernel<ProbT, VT>),
                   dim3(grid_size),
                   dim3(NT),
                   0,
                   stream_,
                   ctc_helper::identity<ProbT>(),
                   probs_,
                   denoms_,
                   out_dim_,
                   num_elements);

hipLaunchKernelGGL 是defined as

template <typename... Args, typename F = void (*)(Args...)>
inline void hipLaunchKernelGGL(F kernel,
                               const dim3& numBlocks,
                               const dim3& dimBlocks,
                               std::uint32_t sharedMemBytes,
                               hipStream_t stream,
                               Args... args) {

// ...
// ...
}

而prepare_stable_SM_kernel 是defined as

template <typename ProbT, int VT = 1, typename Op>
__global__ void prepare_stable_SM_kernel(Op f, ProbT* probs,
                                         const ProbT* const col_max,
                                         int alphabet_size,
                                         int count) {
// ...
}

请任何人提供一些提示来帮助我解决此问题。

【问题讨论】：

什么是(prepare_stable_SM_kernel<ProbT, VT>)？你能把它变成minimal reproducible example吗？
@NathanOliver：事实是，我是 C++11 的初学者，我无法完全理解代码。我已经用prepare_stable_SM_kernel 的定义更新了问题

标签： c++ variadic-templates amd-rocm

【解决方案1】：

通过在prepare_stable_SM_kernel 函数中添加第三个参数ctc_helper::identity<ProbT> 已修复此错误

参考https://github.com/harish2704/warp-ctc/commit/c7ec45febc9c0077ffa35932b3d11a05daf8bf7c#diff-1e372cfc8edab301b6c284e9db8dbf68

【讨论】：