[FFmpeg-devel] [PATCH] Revert "lavu/atomic: add support for the new memory model aware gcc built-ins"

[wm4]

On Tue,  7 Mar 2017 00:29:53 -0300
James Almer <jamrial at gmail.com> wrote:

> This reverts commit faa9d2982969c999ab0e443a226eff116f7f8e4b.
> 
> This change became superfluous when support for C11 atomics was introduced.
> Reverting it will make the removal of this implementation in an upcoming
> merge conflict free.
> 
> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
>  configure              |  4 +---
>  libavutil/atomic_gcc.h | 17 -----------------
>  2 files changed, 1 insertion(+), 20 deletions(-)
> 
> diff --git a/configure b/configure
> index 0199fec5c0..6350942ef9 100755
> --- a/configure
> +++ b/configure
> @@ -1821,7 +1821,6 @@ ARCH_FEATURES="
>  
>  BUILTIN_LIST="
>      atomic_cas_ptr
> -    atomic_compare_exchange
>      machine_rw_barrier
>      MemoryBarrier
>      mm_empty
> @@ -2322,7 +2321,7 @@ symver_if_any="symver_asm_label symver_gnu_asm"
>  valgrind_backtrace_deps="!optimizations valgrind_valgrind_h"
>  
>  # threading support
> -atomics_gcc_if_any="sync_val_compare_and_swap atomic_compare_exchange"
> +atomics_gcc_if="sync_val_compare_and_swap"
>  atomics_suncc_if="atomic_cas_ptr machine_rw_barrier"
>  atomics_win32_if="MemoryBarrier"
>  atomics_native_if_any="$ATOMICS_LIST"
> @@ -5533,7 +5532,6 @@ if ! disabled network; then
>  fi
>  
>  check_builtin atomic_cas_ptr atomic.h "void **ptr; void *oldval, *newval; atomic_cas_ptr(ptr, oldval, newval)"
> -check_builtin atomic_compare_exchange "" "int *ptr, *oldval; int newval; __atomic_compare_exchange_n(ptr, oldval, newval, 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)"
>  check_builtin machine_rw_barrier mbarrier.h "__machine_rw_barrier()"
>  check_builtin MemoryBarrier windows.h "MemoryBarrier()"
>  check_builtin sarestart signal.h "SA_RESTART"
> diff --git a/libavutil/atomic_gcc.h b/libavutil/atomic_gcc.h
> index 5f9fc49ba0..2bb43c3cea 100644
> --- a/libavutil/atomic_gcc.h
> +++ b/libavutil/atomic_gcc.h
> @@ -28,40 +28,27 @@
>  #define avpriv_atomic_int_get atomic_int_get_gcc
>  static inline int atomic_int_get_gcc(volatile int *ptr)
>  {
> -#if HAVE_ATOMIC_COMPARE_EXCHANGE
> -    return __atomic_load_n(ptr, __ATOMIC_SEQ_CST);
> -#else
>      __sync_synchronize();
>      return *ptr;
> -#endif
>  }
>  
>  #define avpriv_atomic_int_set atomic_int_set_gcc
>  static inline void atomic_int_set_gcc(volatile int *ptr, int val)
>  {
> -#if HAVE_ATOMIC_COMPARE_EXCHANGE
> -    __atomic_store_n(ptr, val, __ATOMIC_SEQ_CST);
> -#else
>      *ptr = val;
>      __sync_synchronize();
> -#endif
>  }
>  
>  #define avpriv_atomic_int_add_and_fetch atomic_int_add_and_fetch_gcc
>  static inline int atomic_int_add_and_fetch_gcc(volatile int *ptr, int inc)
>  {
> -#if HAVE_ATOMIC_COMPARE_EXCHANGE
> -    return __atomic_add_fetch(ptr, inc, __ATOMIC_SEQ_CST);
> -#else
>      return __sync_add_and_fetch(ptr, inc);
> -#endif
>  }
>  
>  #define avpriv_atomic_ptr_cas atomic_ptr_cas_gcc
>  static inline void *atomic_ptr_cas_gcc(void * volatile *ptr,
>                                         void *oldval, void *newval)
>  {
> -#if HAVE_SYNC_VAL_COMPARE_AND_SWAP
>  #ifdef __ARMCC_VERSION
>      // armcc will throw an error if ptr is not an integer type
>      volatile uintptr_t *tmp = (volatile uintptr_t*)ptr;
> @@ -69,10 +56,6 @@ static inline void *atomic_ptr_cas_gcc(void * volatile *ptr,
>  #else
>      return __sync_val_compare_and_swap(ptr, oldval, newval);
>  #endif
> -#else
> -    __atomic_compare_exchange_n(ptr, &oldval, newval, 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
> -    return oldval;
> -#endif
>  }
>  
>  #endif /* AVUTIL_ATOMIC_GCC_H */

Sounds like a good thing.