performance impact of "inline" function with "fastcall" calling convension

Question

I have a CRC calculation function which gets called with extremely high frequency. I have already declared as inline i tried making it a __attribute((hot))__ but i am not sure if that buys anything. I am thinking about making it a fastcall.

According to gcc docs ,

fastcall On the Intel 386, the fastcall attribute causes the compiler to pass the first argument (if of integral type) in the register ECX and the second argument (if of integral type) in the register EDX. Subsequent and other typed arguments are passed on the stack. The called function will pop the arguments off the stack. If the number of arguments is variable all arguments are pushed on the stack.

fastcall would make it essentially faster because input params would be sent through registers instead of pushing them on to the stack. with inline, compiler would replace the function call with the body of the function .

So question is does fastcall when used with inline even make sense ?

Answer 1

If you make your function inline, the compiler will simply "paste" it wherever you write it, as you've said.

Therefore, nothing will get called, and so using fastcall would be pointless.