[NSWI004] static inline

[Kryštof Višňák]

Sorry for necroing this thread but would like to ask a related question.
Is it ok to use assembly in inlined functions (sometimes the
compiler inlines even functions that do not have the inline keyword
strapped to them)?

Specifically, can I safely assume that the $a0 register holds
the first parameter? I bumped into this problem when trying to write
a wrapper function around ll/sc instructions. It seems to be working fine
but may not be best practice.

Thanks in advance
KV

út 10. 11. 2020 v 14:55 odesílatel Lubomír Bulej <bulej at d3s.mff.cuni.cz> napsal:
>
> Hi,
>
> TLDR: they are normal functions, except they are very likely to be inlined.
>
>
> Each of the modifiers tells the compiler something about the function.
>
> "static" tells the compiler that the function is private to the compilation
> unit, i.e., it cannot be called from outside the file it is used to.
>
> "inline" is a hint for the compiler suggesting to inline the function when
> called. That keyword is relatively old and as compiler technology advanced,
> the compilers were typically able to make better decisions about whether to
> inline a function or not, especially for functions that are "public", i.e.,
> exported. Modern compilers are therefore likely to ignore the hint on
> non-static functions.
>
> When used together, "static inline" tells the compiler that a function is
> local to a compilation unit (i.e., cannot be called from outside) and that it
> would be nice to inline it, which the compilers (even modern ones) are much
> more likely to respect. The function then effectively becomes a snippet of
> code that can be inlined whenever needed.
>
> This allows removing function call overhead for functions that just hide
> implementation details, but are otherwise so short that the function call
> overhead would be comparable to what the function is actually doing.
>
> For example, in the case of the list implementation, many of the operations
> just rewire pointers, so they compile to a few (small units) instructions.
>
> This is one of the few cases (at least in C) in which code is allowed to live
> in a header file, because it is meant to provide a private copy of the code to
> any source file that uses it. The compiler throws away the unused functions
> (they are all static), and inlines those that are used, thanks to the "static
> inline" hint combined with small size of those functions.
>
>
>
> Best regards,
> Lubomir
>
>
> On 10/11/2020 13:11, Káně, Vojtěch wrote:
> > Hello,
> > I would like to ask what exactly static inline functions are. They are used in
> > include/adt/list.h for example. I did some research on my own, but all the
> > answers were mixing ANSI C, GNU C and C++ together so I got confused even more.
> >
> > I am asking just out of curiosity, it is not blocking my implementation.
> >
> > Thank you in advance,
> > Vojtěch Káně
> >
>
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