Re: [PATCH] compiler, clang: Add always_inline attribute to inline

[Sodagudi Prasad]

On 2017-06-19 13:25, David Rientjes wrote:
> On Mon, 19 Jun 2017, Prasad Sodagudi wrote:
>
> > Commit abb2ea7dfd82 ("compiler, clang: suppress warning for unused
> > static inline functions") re-defining the 'inline' macro but
> > __attribute__((always_inline)) is missing. Some compilers may
> > not honor inline hint if always_iniline attribute not there.
> > So add always_inline attribute to inline as done by
> > compiler-gcc.h file.
>
> IIUC, __attribute__((always_inline)) was only needed for gcc versions < 
> 4
> and that the inlining decision making is improved in >= 4.  To make a
> change like this, I would think that we would need to show that clang 
> is
> making suboptimal decisions.  I don't think there's a downside to 
> making
> CONFIG_OPTIMIZE_INLINING specific only to gcc.
>
> If it is shown that __attribute__((always_inline)) is needed for clang 
> as
> well, this should be done as part of compiler-gcc.h to avoid duplicated
> code.

Hi David,

Here is the discussion about this change -  
https://lkml.org/lkml/2017/6/15/396
Please check mark and will's comments.

-Thanks, Prasad

> > Signed-off-by: Prasad Sodagudi <psodagud@xxxxxxxxxxxxxx>
> > ---
> >  include/linux/compiler-clang.h | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/include/linux/compiler-clang.h 
> > b/include/linux/compiler-clang.h
> > index d614c5e..deb65b3 100644
> > --- a/include/linux/compiler-clang.h
> > +++ b/include/linux/compiler-clang.h
> > @@ -22,4 +22,9 @@
> >   * directives.  Suppress the warning in clang as well.
> >   */
> >  #undef inline
> > +#if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) ||		\
> > +    !defined(CONFIG_OPTIMIZE_INLINING)
> > +#define inline inline __attribute__((always_inline)) 
> > __attribute__((unused)) notrace
> > +#else
> >  #define inline inline __attribute__((unused)) notrace
> > +#endif

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