[C++4OpenCL] Cannot use struct as kernel parameter when accessing through templated struct

[biggysmith]

Hi,

I'm having some issues when using certain types as kernel parameters. Whenever I try to use a struct defined in template type I get compile errors:

struct test_param0{
public:
    struct constants_t{
        int size;
    };
};

template<typename T>
struct test_param1{
public:
    struct constants_t{
        int size;
    };
};

// this compiles fine
kernel void test_kernel0(               
    __read_only image3d_t src_volume, 
    __write_only image3d_t dst_img,  
    __constant test_param0::constants_t& c
)              
{        
} 

// this does not compile
// error: '__constant test_param1<int>::constants_t &__private' cannot be used as the type of a kernel parameter'
kernel void test_kernel1(               
    __read_only image3d_t src_volume, 
    __write_only image3d_t dst_img,  
    __constant test_param1<int>::constants_t& c
)              
{        
} 

Is this some sort of OpenCL C++ limitation? It feels like it should be ok.

--
cmd: clang -target spirv64 -emit-llvm -cl-std=clc++2021 -O0 -c -o output.bc input.clcpp
using llvm 15

[llvmbot]

@llvm/issue-subscribers-opencl

[AnastasiaStulova]

That's right, I can't see anything in the documentation stating that your example should be disallowed. The only relevant restrictions I can see from here https://www.khronos.org/opencl/assets/CXX_for_OpenCL.html#kernel_function are:

Moreover the types used in parameters of the kernel functions must be:

Trivial and standard-layout types C++17 [basic.types] (plain old data types) for parameters passed by value;

Standard-layout types for pointer parameters. The same applies to references[[2](https://www.khronos.org/opencl/assets/CXX_for_OpenCL.html#_footnotedef_2)] if an implementation supports them in kernel parameters.

None of which corresponds to your case. This seems like a clang bug indeed.

[AnastasiaStulova]

This patch seems to be fixing the reported test case but unfortunately it doesn't unlock general use of templates in kernel argument yet: https://reviews.llvm.org/D134445.

FYI as a workaround there is the following extension: https://clang.llvm.org/docs/LanguageExtensions.html#cl-clang-non-portable-kernel-param-types that can be used to enable/disable such diagnostics While I don't advertise using this extension widely it might be useful as s temporary solution while the proper fix of the diagnostics is in progress.

This example compiles with clang-15:

#pragma OPENCL EXTENSION __cl_clang_non_portable_kernel_param_types : enable
kernel void test_kernel1(               
    __read_only image3d_t src_volume, 
    __write_only image3d_t dst_img,  
    __constant test_param1<int>::constants_t& c
)              
{        
}
#pragma OPENCL EXTENSION __cl_clang_non_portable_kernel_param_types : disable

[biggysmith]

I just tried this out in my more complicated example code and it works! I check manually that the struct is standard_layout, so I think this will be safe for me to use for now.

Thanks for investigating this for me.

[AnastasiaStulova]

Fixed in: https://reviews.llvm.org/rG790cbaafc9e276aa740373c00849951338056174

[AnastasiaStulova]

Opened related issue to fix general problem: #58590