Howto pass flag to nvcc compiler in CMAKE

Question

I have a C project in Cmake in which I have embedded cuda kernel module.

I want to pass --ptxas-options=-v only to nvcc in-order to view Number of registers usage per thread and shared Memory usage per block.

By searching on howto pass flags to nvcc in Cmake, I came across a solution

add_compile_options(myprog
    PRIVATE
    $<$<COMPILE_LANGUAGE:C>:-Wall>
    $<$<COMPILE_LANGUAGE:CUDA>:-arch=sm_20 -ptxas-options=-v>
)

but this didn't show me the above properties. I think these flags aren't passed to nvcc properly.

How can I pass --ptxas-options=-v to my nvcc compiler ?

Answer 1

The proper way to set CUDA flags only on a target is

target_compile_options(<my_target> PRIVATE $<$<COMPILE_LANGUAGE:CUDA>:my_cuda_option>) 

This will set the option, via the generator expression, only for files which are compiled for the CUDA language.

Using CMAKE_CUDA_FLAGS as suggested by the other answer sets a global property for all targets, which might or might not be the right approach depending on the use-case.

Answer 2

The newer approach of cmake cuda sets some other variables. Check the docs here.

What we need is to set CMAKE_<LANG>_FLAGS, which actually CMAKE_CUDA_FLAGS here.

set(CMAKE_CUDA_FLAGS "${CMAKE_CUDA_FLAGS} --ptxas-options=-v")