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Re: [patch] Move lowering of switches to bit tests to GIMPLE
On Tue, 2012-07-24 at 08:34 -0700, Richard Henderson wrote:
> On 07/21/2012 06:10 AM, Oleg Endo wrote:
> > I think on SH the cost test in lshift_cheap_p with
> > gen_rtx_ASHIFT (word_mode, const1_rtx, reg), speed_p);
> >
> > will always 'fail', because of sh.c (shiftcosts):
> > /* There is no pattern for constant first operand. */
> > if (CONST_INT_P (XEXP (x, 0)))
> > return MAX_COST;
> >
> > On SH3 / SH4* / SH2A there is a dynamic shift that does "reg << reg" or
> > "reg >> reg", which is not that expensive actually. However, the
> > constant "1" must be loaded into a register first. I'm currently trying
> > to brush up the shift code in SH a little bit and could add some things
> > to handle the "const << reg" case.
>
> Having to load the "1" into a register is something common to all targets.
> I shouldn't think that SH should need to do anything special.
Nope, nothing special. Just load '1' into a reg.
> Indeed, that
> conditional that you quote above looks very wrong. I believe you should
> simply recurse (or let the rtx_cost driver recurse) to find the cost of
> arguments to the shift.
Thanks for the hint. I'll try it out. If it doesn't work I'll just
handle the case 'manually'.
Cheers,
Oleg