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
