https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78655
--- Comment #12 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Jeffrey A. Law from comment #11) > We can assume that the result of a POINTER_PLUS is non-null if either > argument is non-null. So X + constant is always non-null. X + Y would be > non-null if either X or Y is known to be non-null. > > If we know that X + Y is non-null via some mechanism (for example the result > was dereferenced), then we know that X and Y are non-null. Yes, that summarizes it. Note this only applies when !targetm.addr_space.zero_address_valid. There non-null plus a negative offset may yield null. Btw, the old VRP did this already, so I wonder whether it isn't already handled correctly (minus the addr space thing maybe).
