On Fri, Oct 11, 2013 at 11:43 AM, Richard Sandiford
<rdsandif...@googlemail.com> wrote:
> Jakub Jelinek <ja...@redhat.com> writes:
>> On Fri, Oct 11, 2013 at 10:17:41AM +0200, Richard Biener wrote:
>>> asm(".alias __sync_synchronize sync_synchronize");
>>
>> It is .set, but not everywhere.
>> /* The MIPS assembler has different syntax for .set. We set it to
>> .dummy to trap any errors. */
>> #undef SET_ASM_OP
>> #define SET_ASM_OP "\t.dummy\t"
>> But perhaps it would require fewer variants than providing inline asm
>> of the __sync_* builtin by hand for all the targets that need it.
>
> Yeah, that's why I prefer the sed approach. GCC knows how to do exactly
> what we want, and what syntax to use. We just need to take its output and
> change the function name.
>
> And like Richard says, parsing top-level asms would be fair game,
> especially if GCC and binutils ever were integrated (for libgccjit.so).
> So using top-level asms seems like putting off the inevitable
> (albeit putting it off further than __asm renaming).
>
> Do either of you object to the sed thing?
Well, ideally there would be a way to not lie about symbol names to GCC.
That is, have a "native" way of telling GCC what to do here (which is
as far as I understand to emit the code for the builtin-handled $SYM
in a function with $SYM - provide the out-of-line copy for a builtin).
For the __sync functions it's unfortunate that the library function has
the same 'name' as the builtin and the builtin doesn't have an alternate
spelling. So - can't we just add __builtin__sync_... spellings and use
__sync_synchronize ()
{
__builtin_sync_syncronize ();
}
? (what if __builtin_sync_syncronize expands to a libcall? if it can't,
what's the point of the library function?)
Why does a simple
__sync_synchronize ()
{
__sync_synchronize ();
}
not work? On x86_64 I get from that:
__sync_synchronize:
.LFB0:
.cfi_startproc
mfence
ret
.cfi_endproc
(similar to how you can have a definition of memcpy () and have
another memcpy inside it inline-expanded)
Richard.
> Thanks,
> Richard
