Only write changing parts of kernel arguments to kernel CRA

[sophimao]

No description provided.

[zibaiwan]

Thanks Sophie. The overall PR looks good to me. Just one comment regarding using C code vs C++ code. I think since the Runtime have migrated to C++, we probably want to adopt C++ features in the case. Like using new&delete vs malloc&free, it's recommended to never use malloc in C++ due to a number of reasons.

For example

Instead of using
kern->kernel_arg_cache = (char **)acl_malloc(kern->num_accel * sizeof(char *));

Maybe use

kern->kernel_arg_cache = new char*[kern->num_accel](); Note: The () at the end should initialize each of the pointer to nullptr for you.

Don't forget to use delete [] for the array and delete each pointer.

While I am typing those, I feel I don't want to handle memory management myself already. I feel it's better to use the modern C++ feature unique_ptr and vector here as the underlying type of kernel_arg_cache.

I will let you decide.

[sophimao]

Thanks Zibai for the suggestion! I think it's definitely valid, but I might submit that as a separate change in another PR as there are a lot of members of acl_kernel_if that currently still use malloc. In the separate change I might just update everything at once.