On Tue, 2009-12-22 at 09:10 -0500, Daniel Jacobowitz wrote: > On Tue, Dec 22, 2009 at 12:09:55PM +0000, Paul Brook wrote: > > i.e. the following will work as expected: > > > > (define_insn "*my_movsi" > > (set (match_operand:SI "..." "=a,b") > > (match_operand:SI "..." "ab,ab"))) > > > > However the following will not. Once gcc has picked a particular insn > > (_a or _b), it will tend to stick with it and not try other patterns. > > This is my understanding too - but it's a real nuisance. Suppose you > have two optional ISA extensions that have their own move > instructions. For the sake of conversation I'll call them Alice and > Bob... no, I'll call them TARGET_MAVERICK and TARGET_NEON. Now you > need a minimum of three copies of the mov<mode> pattern that are > mostly the same. > > It'd be nice if there was a way to compose instruction patterns :-( > There is. Look at attribute "enabled".
I've not worked out how to use that properly yet, but it is used in the m68k back-end. R.
