On (11/09/12 19:53), Phil Blundell wrote:
> On Tue, 2012-09-11 at 11:40 -0700, Khem Raj wrote:
> > On Tue, Sep 11, 2012 at 9:13 AM, Koen Kooi <k...@dominion.thruhere.net>
> > wrote:
> > > From a gcc point of view both are the same ISA, but using xscale will
> > > take in account the absurdly long pipeline on that SoC.
> >
> > Not really, when you tune for XScale it will use ldrd/strd and pld if
> > possible
>
> Are you sure? As far as I remember, the only effects of -mtune=xscale
> are to alter some minor pipeline-related tradeoffs in code generation.
> In particular, LDM is especially slow on xscale so it is usually best
> avoided unless loading very large numbers of registers.
yes that seems to be right looking at trunk and it does not prefer
LDRD/STRD/PLD too.
so all my claims are not valid anymore.
const struct tune_params arm_xscale_tune =
{
arm_xscale_rtx_costs,
xscale_sched_adjust_cost,
2, /* Constant limit. */
3, /* Max cond insns. */
ARM_PREFETCH_NOT_BENEFICIAL,
true, /* Prefer constant pool. */
arm_default_branch_cost,
false /* Prefer LDRD/STRD. */
};
>
> I can't think of any reason why pld would be any more beneficial on
> xscale than generic v5TE, and I don't think gcc does anything special
> with it in that regard.
>
> p.
>
>
--
-Khem
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