Re: Understanding IRA

[Jeff Law <law at redhat dot com>]

On 11/04/09 10:14, Vladimir Makarov wrote:
> I am agree with Jeff.  It is hard to understand what you are doing 
> without the architecture knowledge and some macro values in your port 
> (IRA_COVER_CLASSES, MEMORY_MOVE_COST, and REGISTER_MOVE_COST).
>
> I'd also add that besides right macro value definitions, you could use 
> insn alternative hints near register constraints like ? or even *.
I was wondering about the constraints in particular.  ISTM that for 
insns where TOP_REGS and BOTTOM_REGS have differing costs that the 
constraint letters for TOP_REGS ought to have a '?' to show they're 
slightly more costly than BOTTOM_REGS.

Alternately IRA_HARD_REGNO_ADD_COST_MULTIPLER might be used to get 
BOTTOM_REGS preferred without having to add a zillion '?' modifiers to 
the constraints in the machine description.

jeff