Excerpts from Nicholas Piggin's message of April 22, 2020 4:18 pm: > If we go further and try to preserve r3 as well by putting the return > value in r9 or r0, we go backwards about 300 bytes. It's good for the > lock loops and complex functions, but hurts a lot of simpler functions > that have to add 'mr r3,r9' etc. > > Most of the time there are saved non-volatile GPRs around anyway though, > so not sure which way to go on this. Text size savings can't be ignored > and it's pretty easy for the kernel to do (we already save r3-r8 and > zero them on exit, so we could load them instead from cache line that's > should be hot). > > So I may be inclined to go this way, even if we won't see benefit now.
By, "this way" I don't mean r9 or r0 return value (which is larger code), but r3 return value with r0,r4-r8 preserved. Thanks, Nick
