On Thu, Aug 15, 2019 at 4:17 PM Jan Hubicka <hubi...@ucw.cz> wrote: > > > On Tue, Aug 6, 2019 at 5:44 PM Martin Liska <mli...@suse.cz> wrote: > > > > > > > > > gcc/ChangeLog: > > > > So I suppose this isn't to call operand_equal_p on two FIELD_DECLs > > but to make two COMPONENT_REFs "more equal"? If so I then > > yes. The patch originates from my original patchset I believe and it is > what ICF does. > > I suggest to make this change "local" to the COMPONENT_REF handling. > > This also interacts with path-based disambiguation so you want to make > > sure to only make things equal here iff it wouldn't change the outcome > > of path-based analysis. Honza? > > Indeed this can be handled as part of COMPONENT_REF match. > Access path oracle here basically checks: > 1) that MEM_REF type matches (we want predicate for this) > 2) if it finds type match via same_type_for_tbaa and then it applies > the assumption about disjointness or overlap > > So I guess ideally we should > > 1) do matching part of COMPONENT_REF > 2) compare OFFSET, BIT_OFFSET > This establishes that the access has same semantics. > 3) for -fno-strict-aliasing be happy > 4) for -fstrict-aliaisng check if access path applies (we should export > predicate from tree-ssa-alias as discussed earlier) > 5) compare types by same_type_for_tbaa_p
Ick. This smells like a layering violation to me. IMHO this extended equality handling should be handled with the overloading/callback and not in native operand_equal_p. Either on the level of the COMPONENT_REF itself (sounds like that would be needed) or the FIELD_DECL. Not sure if the above suggestions make it neccessary to look at more than a single COMPONENT_REF/FIELD_DECL in the access path. If so then watch out for quadraticness as operand_equal_p traverses a reference chain... Richard. > Honza
