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Re: PATCH: PR target/40470: unable to find a registe r to spill in class ‘SSE_FIRST_REG’


On 6/17/09, Jeff Law <law@redhat.com> wrote:
> Richard Guenther wrote:
> > On Wed, Jun 17, 2009 at 4:01 PM, H.J. Lu<hongjiu.lu@intel.com> wrote:
> >
> >
> > > Hi,
> > >
> > > Some SSE4 instructions have implicit XMM0 operand. This patch helps RA
> > > deal with them by forcing operand into XMM0 during expand. OK for trunk
> > > and 4.4?
> > >
> > >
> >
> > I don't think it's a particularly good idea to put things in hardregs
> > that early.
> >
> >
> Agreed.  In fact, it can have horrific performance impacts.

Why? Most optimizazions that can be done for this insn can only be
done on GIMPLE, right?  And the insn must have that specific register.
So unless I am missing something, I don't see why this patch would do
any harm.

I'm guessing HJ looked at performance, anyway...?

Ciao!
Steven


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