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Re: [PATCH] Use lwsync in PowerPC sync_* builtins
On Wed, Sep 3, 2008 at 6:09 PM, David Edelsohn <dje.gcc@gmail.com> wrote:
> On Wed, Sep 3, 2008 at 6:53 PM, Anton Blanchard <anton@samba.org> wrote:
>> The only thing lwsync wont order is a store followed by a load. Since
>> the lwsync will always be paired with a store (the stwcx), we will order
>> all accesses before it and provide a release barrier.
>
> Anton,
>
> My one other concern is developers using the builtins for applications on
> embedded PowerPC processors. lwsync will not order accesses to device
> memory space, AFAICT. I do not know if developers would rely on GCC builtins
> in that context and assume it implements the correct semantics. Otherwise,
> I agree that the memory barrier operations probably can use lwsync.
Would it be possible to have a conservative default and use a more
optimal form based on a specific CPU specified by -mcpu=?
I was thinking of doing something similar on MIPS where there are
similar issues.
David Daney