[Beignet] [PATCH] GBE: avoid vector registers when there is high register pressure.

[Zhigang Gong]

On Mon, Sep 21, 2015 at 11:11:48AM +0800, Ruiling Song wrote:
> It makes sense to use short-live vector register under register pressure.
> But please also remove the comment
> "// If an element has very long interval, we don't want to put it into a
>  // vector as it will add more pressure to the register allocation"

Right, the comments are out-of-date now and need to be removed.
Thanks,
Zhigang Gong.

> 
> Thanks!
> Ruiling
> 2015-09-17 8:39 GMT+08:00 Zhigang Gong <zhigang.gong at linux.intel.com>:
> 
> > Ping for review.
> > Thanks.
> >
> > On Sun, Sep 06, 2015 at 05:21:29PM +0800, Zhigang Gong wrote:
> > > If the reservedSpillRegs is not zero, it indicates we are in a
> > > very high register pressure. Use register vector will likely
> > > increase that pressure and will cause significant performance
> > > problem which is much worse than use a short-live temporary
> > > vector register with several additional MOVs.
> > >
> > > So let's simply avoid use vector registers and just use a
> > > temporary short-live-interval vector.
> > >
> > > Signed-off-by: Zhigang Gong <zhigang.gong at intel.com>
> > > ---
> > >  backend/src/backend/gen_reg_allocation.cpp | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/backend/src/backend/gen_reg_allocation.cpp
> > b/backend/src/backend/gen_reg_allocation.cpp
> > > index 39f1934..36ad914 100644
> > > --- a/backend/src/backend/gen_reg_allocation.cpp
> > > +++ b/backend/src/backend/gen_reg_allocation.cpp
> > > @@ -318,7 +318,7 @@ namespace gbe
> > >        if (it == vectorMap.end() &&
> > >            ctx.sel->isScalarReg(reg) == false &&
> > >            ctx.isSpecialReg(reg) == false &&
> > > -          (intervals[reg].maxID - intervals[reg].minID) < 2048)
> > > +          ctx.reservedSpillRegs == 0 )
> > >        {
> > >          const VectorLocation location = std::make_pair(vector, regID);
> > >          this->vectorMap.insert(std::make_pair(reg, location));
> > > --
> > > 1.9.1
> > >
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