RE: [RFC] eal: use same atomic intrinsics for gcc and clang

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

<snip>

> 
> On Fri, Feb 10, 2023 at 07:56:22PM -0600, Honnappa Nagarahalli wrote:
> > The size generic atomic intrinsics generate the same code as the size
> > specific intrinsics for gcc. Use size generic intrinsics for both gcc
> > and clang.
> >
> > Fixes: 7bdccb93078e ("eal: fix ARM build with clang")
> > Cc: stable@dpdk.org
> > Cc: pbhagavatula@marvell.com
> >
> > Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> 
> Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> 
> so first of all thanks for fixing this up. it was confusing me why it was being
> conditionally compiled (there was no documented rationale).
> 
> i do have a slight concern that perhaps the reason this was done was because
> __atomic_exchange_n on some gcc versions or for some specific target
> processor was generating less than desirable code but if nobody else has this
> concern i won't get in the way since it simplifies things.
Agree, I could not find a rationale from the commit logs. However, I did some tests on Godbolt and the latest compilers generated the same code for both the variants for x86 and ARM.
I think the initial author was Stephen, may be he has some comments.

> 
> thanks!
> 
> > ---
> >  lib/eal/include/generic/rte_atomic.h | 12 ------------
> >  1 file changed, 12 deletions(-)
> >
> > diff --git a/lib/eal/include/generic/rte_atomic.h
> > b/lib/eal/include/generic/rte_atomic.h
> > index f5c49a9870..234b268b91 100644
> > --- a/lib/eal/include/generic/rte_atomic.h
> > +++ b/lib/eal/include/generic/rte_atomic.h
> > @@ -176,11 +176,7 @@ rte_atomic16_exchange(volatile uint16_t *dst,
> > uint16_t val);  static inline uint16_t  rte_atomic16_exchange(volatile
> > uint16_t *dst, uint16_t val)  { -#if defined(__clang__)
> >  	return __atomic_exchange_n(dst, val, __ATOMIC_SEQ_CST); -#else
> > -	return __atomic_exchange_2(dst, val, __ATOMIC_SEQ_CST);
> > -#endif
> >  }
> >  #endif
> >
> > @@ -459,11 +455,7 @@ rte_atomic32_exchange(volatile uint32_t *dst,
> > uint32_t val);  static inline uint32_t  rte_atomic32_exchange(volatile
> > uint32_t *dst, uint32_t val)  { -#if defined(__clang__)
> >  	return __atomic_exchange_n(dst, val, __ATOMIC_SEQ_CST); -#else
> > -	return __atomic_exchange_4(dst, val, __ATOMIC_SEQ_CST);
> > -#endif
> >  }
> >  #endif
> >
> > @@ -741,11 +733,7 @@ rte_atomic64_exchange(volatile uint64_t *dst,
> > uint64_t val);  static inline uint64_t  rte_atomic64_exchange(volatile
> > uint64_t *dst, uint64_t val)  { -#if defined(__clang__)
> >  	return __atomic_exchange_n(dst, val, __ATOMIC_SEQ_CST); -#else
> > -	return __atomic_exchange_8(dst, val, __ATOMIC_SEQ_CST);
> > -#endif
> >  }
> >  #endif
> >
> > --
> > 2.25.1