On Tue, Apr 21, 2015 at 11:55:33PM -0400, Vladimir Makarov wrote: > >The combiner can add or remove clobbers of scratches whenever needed, > >but it cannot do that for clobbers of pseudos. > > > Yes, I think there are some pitfalls with scratches in other passes.
Probably. But this one is documented (under CLOBBER as well as MATCH_SCRATCH) ;-) > As for combiner, it is probably worth to consider processing clobbers of > pseudos with *one* reference as scratches too. The combiner can already remove any clobber when it needs to (to pass recog). It cannot add a clobber of a pseudo -- making it do that requires changing recog (and few lines in combine, if any). Currently, combine can add clobbers of scratches and hard regs, when recog tells it to. In the past combine could not handle any new registers (even though it actually creates some), but Jakub's r220368 should take care of that. > It might improve code > for some cases although I am not sure about this. I don't see how. Maybe there is some sub-optimality in current code, but that can be fixed of course. The concept stays the same: a pseudo that isn't used anywhere else, or a scratch. Same thing, just expressed differently. Getting rid of match_scratch from the RTL passes before RA will be an enormous amount of work, and it will not improve anything (quite the opposite): every define_expand, define_insn, define_split and define_insn_and_split that runs (or can run) before reload, and currently has a match_scratch, will need to be modified. We will need extra expanders everywhere, to match the pattern without the new pseudo, and add a new pseudo. Then we could add some markup so we do not need that, but we already *have* such markup: match_scratch. I'm also not looking forward to checking all RTL passes for regressions. In your last reply to Steven you say that IRA only wants match_scratch with every alternative needed (not "X") to be a pseudo before IRA gets to see it. Can IRA not do this itself? Segher
