[patch][i386] Remove some dead code (TARGET_BRANCH_PREDICTION_HINTS)

Uros Bizjak ubizjak@gmail.com
Tue Jul 10 08:58:00 GMT 2012


On Tue, Jul 10, 2012 at 9:04 AM, Steven Bosscher <stevenb.gcc@gmail.com> wrote:
>>> TARGET_BRANCH_PREDICTION_HINTS isn't used at all. This patch removes it.
>>> Bootstrapped&tested (incl. -m32) on x86_64-unknown-linux-gnu. OK for trunk?
>>
>> This infrastructure can be used for future targets, so let's leave it as is.
>
> Yes, I suppose that's theoretically possible. However, I don't think
> this is very likely to happen. The branch hints only ever were
> supported for P4, but even Intel's own ICC never emits them
> (http://sources.redhat.com/ml/binutils/2004-07/msg00322.html). In
> fact, the whole Netburst microachitecture appears to have been
> abandoned (in favor of the ppro microachitecture).  For EM64T another
> form of branch hints was introduced (which GCC doesn't support and ICC
> doesn't emit).
>
> So any future target that would need this, would have to be a 32-bits,
> deep-pipeline microarchitecture. I personally don't believe that such
> an architecture will emerge, given the history of failure of this
> concept.
>
> Are these arguments reason enough for you to reconsider? :-)

Arguments are indeed good, but I'd like to hear HJ's opinion about
future targets.

Anyway, this functionality can be reimplemented from the scratch for
future target, but OTOH, it is not a mainenance burden at all...

Uros.



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