On Fri, Mar 10, 2017 at 10:30:33AM +0000, Kyrill Tkachov wrote: > I'm trying to improve the cases where the result of the arithmetic > operation is used in multiple places besides the comparison. > For example: > add w0, w0, w1 > add w1, w0, 2 > cmp w0, 0 > > Combine will not attempt to merge the first ADD and CMP because W0 is used > in the second ADD.
So the LOG_LINK from the first instruction will point at the second, and combining the first and the third isn't considered (because the first and second insns don't combine). combine doesn't try to combine all producer-consumer pairs, only producer with first consumer, because it would not often help and could easily take much more time. On the other hand I'd love to get rid of the LOG_LINKS and use DF directly. Note that combining the first and third insns in your example requires to put the combined insns in the place of the first insn, where normally it would put it at the third insn. Maybe we could treat compares specially? Do such cases happen a lot, btw? Segher
