Re: Question on replacing macros with static inline functions
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- Subject: Re: Question on replacing macros with static inline functions
- From: Steffen Nurpmeso <steffen@...>
- Date: 2022年11月17日 23:28:21 +0100
Ah, sorry to be here again. You may surely skip this.
Andrew Cagney wrote in
<CAJeAr6vo7Rzzo+op+J6WBtHko=zobapERXcTq0pSbpy3TGL7pg@mail.gmail.com>:
|> From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
|> Sent: Monday, November 14, 2022 11:45 AM
|> To: Lua mailing list
|> Subject: Re: Question on replacing macros with static inline functions
|>
|>> I noticed that Lua code sometimes uses macros where a static inline \
|>> function
|>> would appear to work equally as well.
|>> [...]
|>>
|>> How interested would the Lua development team be in replacing such \
|>> macros with
|>> functions in the future?
|>
|> Inline functions is not present in C89, and Lua is (still) compatible
|> with C89.
|On 2022年11月14日 at 11:49, Brent Pappas <pappasbrent@knights.ucf.edu> \
|wrote:
|> I see, that makes sense.
|> Thanks for the quick reply.
|
|I'd expect those macros to be around for some time:
|
|- GCC didn't adopt C99 inline semantics until GCC 4.3 and that was
|only released in 2008 https://gcc.gnu.org/gcc-4.3/
|https://gcc.gnu.org/gcc-4.3/porting_to.html ); sticking with macros
|avoids that compatibility headache
But just to note that gcc did support inline by other means many
years earlier, via __inline__. Linkage was a bit messy so you
could do "extern __inline__" or "static __inline__" which was
better but would complain about unused functions iirc. Ie you
could simply have lots of injected static functions without
__inline__ if that would not be supported. Or you did
a tremendous dance of doing "extern myprefix_function()" and
"XYINLINE myinlineprefix_function()", which you could inject only
upon optimization time or when the implementation compiles, and
use preprocessor macros to define myprefix_function() to
myinlineprefix_function() in the former case only. And
myprefix_function() would do nothing but assertions etc and then
call myinlineprefix_function(). (You can still call
myprefix_function() via (myprefix_function)(), ie, for taking the
address.) I think the Linux kernel by that time (~2000) was full
of extern __inline__.
|- putting the stubs in .c files works well with modern compilers (the
|link-time optimizer will eliminate the call), older compilers don't
|support this though and take a hit; sticking to macros avoids this
I personally always felt it was a shame that the ({ .. })
extension of gcc never made it to a standard. But now that C++ is
about to eliminate the preprocessor (as i heard), that ship has
sailed.
P.S.: not to mention that once in a while gcc reintroduces bugs
that some inline functions not actually happen, the latest two
examples (i know of) being an "-Os" inlining bug in March 2019
# if defined __STDC_VERSION__ && __STDC_VERSION__ +0 >= 199901L
...
+ /* xxx gcc 8.3.0 bug: does not truly inline with -Os */
+# if su_CC_GCC && defined __OPTIMIZE_SIZE__
+# define su_INLINE inline __attribute__((always_inline))
+# else
+# define su_INLINE inline
+# endif
and in June this year, when a windriver guy reported something
with -Og (that i did not even know), so now i have finally dropped
it all and only go for what i did for clang always:
...
# elif su_CC_CLANG || su_CC_GCC || su_CC_PCC
# if defined __STDC_VERSION__ && __STDC_VERSION__ +0 >= 199901l
# if !defined NDEBUG || !defined __OPTIMIZE__
# define su_INLINE static inline
# define su_SINLINE static inline
# else
/* clang does not like inline with <-O2 */
# define su_INLINE inline __attribute__((always_inline))
# define su_SINLINE static inline __attribute__((always_inline))
# endif
# else
# if su_CC_VCHECK_GCC(3, 1)
# define su_INLINE static __inline __attribute__((always_inline))
# define su_SINLINE static __inline __attribute__((always_inline))
# else
# define su_INLINE static __inline
# define su_SINLINE static __inline
# endif
# endif
...
# endif
Actually i have lost track. But twenty years ago it worked
flawless as stated above. (But which was _tremendous_ work.)
Ciao.
--steffen
|
|Der Kragenbaer, The moon bear,
|der holt sich munter he cheerfully and one by one
|einen nach dem anderen runter wa.ks himself off
|(By Robert Gernhardt)