Is restrict(amp) more restrictive than CUDA kernel code? - parallel-processing

Question

In C++ AMP, kernel functions or lambdas are marked with restrict(amp), which imposes severe restrictions on the allowed subset of C++ (listed here). Does CUDA allow any more freedom on the subset of C or C++ in kernel functions?

Answer 1

As of Visual Studio 11 and CUDA 4.1, restrict(amp) functions are more restrictive than CUDA's analogous __device__ functions. Most noticeably, AMP is more restrictive about how pointers can be used. This is a natural consequence of AMP's DirectX11 computational substrate, which disallows pointers in HLSL (graphics shader) code. By constrast, CUDA's lower-level IR is PTX, which is more general purpose than HLSL.
Here's a line by line comparison:
| VS 11 AMP restrict(amp) functions | CUDA 4.1 sm_2x __device__ functions |
|------------------------------------------------------------------------------|
|* can only call functions that have |* can only call functions that have |
| the restrict(amp) clause | the __device__ decoration |
|* The function must be inlinable |* need not be inlined |
|* The function can declare only |* Class types are allowed |
| POD variables | |
|* Lambda functions cannot |* Lambdas are not supported, but |
| capture by reference and | user functors can hold pointers |
| cannot capture pointers | |
|* References and single-indirection |* References and multiple-indirection |
| pointers are supported only as | pointers are supported |
| local variables and function | |
|* No recursion |* Recursion OK |
|* No volatile variables |* Volatile variables OK |
|* No virtual functions |* Virtual functions OK |
|* No pointers to functions |* Pointers to functions OK |
|* No pointers to member functions |* Pointers to member functions OK |
|* No pointers in structures |* Pointers in structures OK |
|* No pointers to pointers |* Pointers to pointers OK |
|* No goto statements |* goto statements OK |
|* No labeled statements |* Labeled statements OK |
|* No try, catch, or throw statements |* No try, catch, or throw statements |
|* No global variables |* Global __device__ variables OK |
|* Static variables through tile_static |* Static variables through __shared__ |
|* No dynamic_cast |* No dynamic_cast |
|* No typeid operator |* No typeid operator |
|* No asm declarations |* asm declarations (inline PTX) OK |
|* No varargs |* No varargs |
You can read more about restrict(amp)'s restrictions here. You can read about C++ support in CUDA __device__ functions in Appendix D of the CUDA C Programming Guide.