> On Fri, Sep 20, 2013 at 6:00 AM, Zamyatin, Igor <igor.zamya...@intel.com>
> wrote:
> >
> > For x86 32-bit is still important due to mobile market so we would like to
> > make some measurements first to see how this new generic model works on 32
> > bits
I assume by mobile market you mean atom CPU these days (not Pentium-M generic32
was tuned for).
>
> I would expect people compiling code for the mobile market to use an
> appropriate -mtune option. What this patch affects is the default
> tuning.
I agree here. Moreover the 32bit generic model is not at all that new. It is
same as the old code only flipping the four flags I mentioned plus changing the
scheduling to K8 instead of PPro based model. The flags changed are:
use_leave - this was there because pentium-M was slow on leave instructions.
How does atom behave here?
avoid_vector_decode - this is affecting gneration of integer->FP conversions
K8 preferred to use vector instructions to avoid penalty.
We now enable the flag:
m_CORE_ALL | m_K8 | m_GENERIC64
I suppose we enabled it for Generic as a result of the overall
ideology
of not using instructions in generic that have evil performance
on one of CPUs we consider important for generic.
I think the flag was copied to CORE as a result of core tunning
being
based on generic tuning and hsould be dropped - both from core and
generic based on fact that newer AMD CPUs do not care.
slow_imul_imm32_mem
slow_imul_imm8
This enables splitting of those instructions into move+mul that
should
not be terrible for atom either.
Again, I think this flag is mistakely enabled for core.
I need to dig up the thread we had last year about dropping
some of these - as I recall, all except for inc/dec was fine.
Honza
>
> Ian
