From: "Óscar Fuentes" <ofv@wanadoo.es>
To: emacs-devel@gnu.org
Subject: Re: Emacs' C: static inline considered useless nowadays?
Date: Mon, 17 Oct 2022 05:33:18 +0200 [thread overview]
Message-ID: <87h703f7k1.fsf@telefonica.net> (raw)
In-Reply-To: 87a65vcfbp.fsf@rfc20.org
Matt Armstrong <matt@rfc20.org> writes:
> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>
>> Matt Armstrong [2022-10-16 15:08:51] wrote:
>>> I've spent the last few decades coding with an undersanding that
>>> "inline" is about linkage and allows one to place code in header files
>>> so that it *may* be inlined, but that compilers long ago stopped using
>>> it as a meaningful inlining hint. But this is mostly colored by how gcc
>>> and clang behave with C++, and not much else.
>>
>> I believe what you say does hold true for "optimized builds".
>> I'd be interested to know if it's true for lower levels of optimization
>> as well.
>>
>> Stefan "compiling with -Og"
>
> Seems the answer, thanks to godbolt, is "it depends", but "static
> inline" does enable inlining in gcc's -Og, so it has its use.
>
> For this program:
>
> static inline int static_inline_add(int x, int y) { return x + y; }
> static int static_add(int x, int y) { return x + y; }
> int add_three(int x, int y, int z) {
> return static_add(x, static_inline_add(y, z));
> }
>
> gcc and clang has the same behavior:
>
> -O0: nither static functions are inlined into 'add_three'
> -Og: only 'static_inline_add' is inlined
> -O1: 'static_add' is also inlined
See https://gcc.gnu.org/onlinedocs/gcc/Inline.html for some enlightening
comments on this topic.
Please note that modern compilers implement complex heuristics for
deciding when a function is inlined (and the presence of the `inline'
keyword is just another factor.) An "static inline" function may not be
inlined even at -O2 if your compiler decides that it is better left
un-inlined.
next prev parent reply other threads:[~2022-10-17 3:33 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-16 22:08 Emacs' C: static inline considered useless nowadays? Matt Armstrong
2022-10-17 0:43 ` Stefan Monnier
2022-10-17 3:13 ` Matt Armstrong
2022-10-17 3:33 ` Óscar Fuentes [this message]
2022-10-17 6:10 ` Eli Zaretskii
2022-10-17 19:08 ` Matt Armstrong
2022-10-17 19:12 ` Eli Zaretskii
2022-10-17 20:33 ` Matt Armstrong
2022-10-18 2:30 ` Eli Zaretskii
2022-10-18 13:32 ` Stefan Monnier
2022-10-18 15:09 ` Eli Zaretskii
2022-10-18 17:01 ` tomas
2022-10-18 19:22 ` Stefan Monnier
2022-10-18 19:31 ` Eli Zaretskii
2022-10-18 11:58 ` Richard Stallman
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