On Mon, Jul 30, 2012 at 08:21:40PM +0100, Jamie Lokier wrote: > Paul E. McKenney wrote: > > > Does some version of gcc, under the options which we insist upon, > > > make such optimizations on any of the architectures which we support? > > > > Pretty much any production-quality compiler will do double-fetch > > and old-value-reuse optimizations, the former especially on 32-bit > > x86. I don't know of any production-quality compilers that do value > > speculation, which would make the compiler act like DEC Alpha hardware, > > and I would hope that if this does appear, (1) we would have warning > > and (2) it could be turned off. But there has been a lot of work on > > this topic, so we would be foolish to rule it out. > > GCC documentation for IA-64: > > -msched-ar-data-spec > -mno-sched-ar-data-spec > (En/Dis)able data speculative scheduling after reload. This results > in generation of ld.a instructions and the corresponding check > instructions (ld.c / chk.a). The default is 'enable'. > > I don't know if that results in value speculation of the relevant kind. If I remember correctly, the chk.a instruction will detect failed speculation via cache state and deal with the situation correctly, but I really need to defer to someone with more recent IA-64 experience. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
