On Fri, 2017-01-13 at 23:22 +0530, 'Naveen N. Rao' wrote:

quoted

That rather depends on whether the processor has a store to load forwarder
that will satisfy the read from the store buffer.
I don't know about ppc, but at least some x86 will do that.

Interesting - good to know that.

However, I don't think powerpc does that and in-register swap is likely 
faster regardless. Note also that gcc prefers this form at higher 
optimization levels.

Of course powerpc has a load-store forwarder these days, however, I
wouldn't be surprised if the in-register form was still faster on some
implementations, but this needs to be tested.

Ideally, you'd want to try to "optimize" load+swap or swap+store
though.

Cheers,
Ben.