"Erich Plondke" <[EMAIL PROTECTED]> writes: > * Combine doesn't pick tuples of three to attempt to combine, so it > would never > pick mult, plus, and ashift to try together.
Actually, combine does try to put pairs and triplets of instructions together. It won't do four instructions at once, though. > * Combine doesn't put an instruction back to try and combine again, > so once I get "mac" > combine doesn't try again to find "mac_s16". No, actually, it will do this. It is possible to build up combinations through a sequence of insn patterns. I don't know why it didn't combine for you. You will have look at the RTL debugging dump to figure it out. A common problem is that combine will normally only combine two or three SETs if the destination register of the earlier one dies in the later one. (Technically it will try to putting together a PARALLEL of the combined instruction and the initial SET, but this rarely matches.) Another occasional problem is that combine will only do a combination if the resulting instruction is cheaper, so you have to make sure that your costs are right. Ian
