On Sun, Jan 17, 2016 at 6:38 AM, Andreas Seltenreich <seltenre...@gmx.de> wrote:
> I'm currently experimenting with just-in-time compilation using libfirm.
> While discussing issues with its developers, it was pointed out to me
> that our spinlock inline assembly is less than optimal.  Attached is a
> patch that addresses this.
> ,----
> | Remove the LOCK prefix from the XCHG instruction.  Locking is implicit
> | with XCHG and the prefix wastes a byte.  Also remove the "cc" register
> | from the clobber list as the XCHG instruction does not modify any flags.
> |
> | Reported by Christoph Mallon.
> `----

I did a Google search and everybody seems to agree that the LOCK
prefix is redundant.  I found a source agreeing with the idea that it
doesn't clobber registers, too:


So I guess it would be safe to change this.  Scares me slightly, though.

Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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