Or how about this version ? Here I use the + modifier and I don't put any
constraints on the input line.
static inline int32_t opal_atomic_add_32(volatile int32_t* v, int i)
{
int ret = i;
__asm__ __volatile__(
SMPLOCK "xaddl %1,%0"
: "+m" (*v), "+r" (ret)
:
: "memory", "cc"
);
return (ret+i);
}
george.
On Feb 23, 2011, at 16:59 , George Bosilca wrote:
> Jay,
>
> Thanks for the code. The code you pointed out is only used during configure,
> so I don't think is that critical. However, we use similar code deep into our
> voodoo assembly generation, for opal_atomic_add_32 and opal_atomic_sub_32.
>
> So if I understand your statement the correct version of the code should be
>
> static inline int32_t opal_atomic_add_32(volatile int32_t* v, int i)
> {
> int ret = i;
> __asm__ __volatile__(
> SMPLOCK "xaddl %1,%0"
> :"=m" (*v), "+r" (ret)
>>> new >> :"m" (*v)
> );
> return (ret+i);
> }
>
> On the GCC extended ASM documentation
> (http://gcc.gnu.org/onlinedocs/gcc/Modifiers.html#Modifiers), it is specified:
>
> `=' Means that this operand is write-only for this instruction: the
> previous value is discarded and replaced by output data.
>
> `+' Means that this operand is both read and written by the instruction.
>
> Based on this info, I would rather rewrite this function like this:
>
> static inline int32_t opal_atomic_add_32(volatile int32_t* v, int i)
> {
> int ret = i;
> __asm__ __volatile__(
> SMPLOCK "xaddl %1,%0"
> : "=m" (*v), "=r" (ret)
> : "m" (*v), "1" (ret)
> : "memory", "cc"
> );
> return (ret+i);
> }
>
> Can you ask the kindly GCC expert which version is "correct" (whatever the
> definition of correct might means related to GCC extended assembly). Do I
> have to specify = for the output if I put the register on the input? Aren't
> this conflicting?
>
> george.
>
> On Feb 23, 2011, at 13:04 , Jay Fenlason wrote:
>
>> I was recently handed
>> https://bugzilla.redhat.com/attachment.cgi?id=480307
>> for which a kindly GCC expert attached the enclosed patch. Apparently
>> this only causes problems on 32-bit i686 machines, which could by why
>> it has gone undetected until now.
>>
>> -- JF
>>
>> --- openmpi-1.5/opal/config/opal_config_asm.m4.jj 2010-09-28
>> 23:33:51.000000000 +0200
>> +++ openmpi-1.5/opal/config/opal_config_asm.m4 2011-02-23
>> 01:39:21.191433509 +0100
>> @@ -885,7 +885,7 @@ AC_DEFUN([OMPI_CONFIG_ASM],[
>> ompi_cv_asm_arch="AMD64"
>> fi
>> OPAL_ASM_SUPPORT_64BIT=1
>> - OMPI_GCC_INLINE_ASSIGN='"xaddl %1,%0" : "=m"(ret), "+r"(negone)'
>> + OMPI_GCC_INLINE_ASSIGN='"xaddl %1,%0" : "=m"(ret), "+r"(negone)
>> : "m"(ret)'
>> ;;
>>
>> ia64-*)
>> _______________________________________________
>> devel mailing list
>> de...@open-mpi.org
>> http://www.open-mpi.org/mailman/listinfo.cgi/devel
>
> "I disapprove of what you say, but I will defend to the death your right to
> say it"
> -- Evelyn Beatrice Hall
>
>
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