Re: [PATCH 5/5] MdePkg/BaseSynchronizationLib GCC: simplify IA32 InternalSyncCompareExchange64()

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 30/09/2018 00:23, Laszlo Ersek wrote:
> The IA32 variant of InternalSyncCompareExchange64() is correct, but we can
> simplify it. We don't need to load the lower 32 bits of ExchangeValue into
> EBX in two steps (first into a general register, then into EBX); we can
> ask GCC to populate EBX like that itself.
> 
> Cc: Liming Gao <liming.gao@intel.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1208
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

> ---
>  MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c b/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c
> index 44188e265af2..af39bdeb516c 100644
> --- a/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c
> +++ b/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c
> @@ -193,14 +193,11 @@ InternalSyncCompareExchange64 (
>    )
>  {
>    __asm__ __volatile__ (
> -    "push        %%ebx      \n\t"
> -    "movl        %2,%%ebx   \n\t"
>      "lock                   \n\t"
>      "cmpxchg8b   (%1)       \n\t"
> -    "pop         %%ebx      \n\t"
>      : "+A"  (CompareValue)                    // %0
>      : "S"   (Value),                          // %1
> -      "r"   ((UINT32) ExchangeValue),         // %2
> +      "b"   ((UINT32) ExchangeValue),         // %2
>        "c"   ((UINT32) (ExchangeValue >> 32))  // %3
>      : "memory",
>        "cc"
>