https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69847
--- Comment #10 from Vladimir Makarov <vmakarov at gcc dot gnu.org> --- I've been working on this for about 2 weeks and still I don't see the problem will be solved soon. Therefore I've decided to write some update. First of all after analyzing hot functions, I found that LRA generates more code to load high parts of addresses than the reload pass. Digging into the reload pass I found that the reload does an inheritance beyond memory load/stores and reuse values in pseudos containing an address high part where it is possible. This functionality is missed in LRA. I started to think how to better implement it in LRA (inheritance or rematerialization) but I came to the conclusion that the inheritance is the only way to do this. Unfortunately, inheritance in LRA is a complicated thing and I need to make it even more complicated. I almost finished the implementation of the inheritance beyond the spills. Unfortunately, I found that even LRA generates fewer insns and loads of address high parts for the code examples, there are still additional reg-reg moves in comparison with the code generated by the reload pass. I think removing these additional moves will require changes in LRA assignment sub-pass. Currently LRA assigns hard registers to reload pseudos first (to guarantee they will get hard registers in any case) and then to inheritance pseudos. To remove the moves, assignment to reload pseudos and inheritance pseudos connected to the reload pseudos should be assigned at the same time (or one immediately after another). It means that we need to able to spill the inheritance pseudos (or assign it to other registers) if another reload pseudo needs an inheritance pseudo register. So I am going to try this new assignment scheme. ETA for this is June-July.
