On Thu, Feb 10, 2022 at 05:21:07PM +0100, Jakub Jelinek wrote: > On Thu, Feb 10, 2022 at 10:10:13AM -0600, Segher Boessenkool wrote: > > But we do have that in other cases, and not just for combine. IMO it > > is a good idea to robustify for_each_inc_dec (simply have it skip if the > > address is not MODE_INT or such). It also is a good idea to robustify > > combine subst, just as you do. It is best to do both! > > Well, skipping would mean the callback isn't called on it so the autoinc > isn't detected.
Which is fine, because it isn't valid in the first place! The only thing we have to do is not ICE, this RTL is not long for this world. > > So does it not fail if you make this valid code (by using another > > register)? bp, si, or di maybe? > > Not on x86, that isn't a general auto-inc-dec target, but uses PRE_DEC > etc. only for the sp hard register. Ugh. Does it have any benefit from using autoinc at all then? (Actual benefit, not notational convenience). > For other targets we'd need to somehow convince all the earlier passes > (gimple and RTL) not to try to propagate the constant value into the > addition inside of a memory address. I wonder if there is any target for which autoinc is more convenient than inconvenient (other than in inline asm, a whole separate challenge) :-( Segher
