goldsteinn wrote: > High level question: Are all of these really useful? > > For parameter attributes, there are really two types, ones that are used to > reason about calls, and ones used to reason about function definitions. I > think the split here is something like: > > * readonly/readnone: Mostly used for calls. Since recently used for > definitions in conjunction with noalias. > * writeonly: Used for calls. > * range, dereferenceable_or_null: Used for definitions. > * align: Mostly used for definitions, but also used for intrinsic calls. > * nonnull, dereferenceable: Mostly used for definitions. Used for calls in > conjunction with noundef for "dominating conditions" in isKnownNonZero. > > Based on that breakdown, I can see some usefulness for propagating the > readonly family, align and nonnull/dereferenceable. > > Is there anything that propagating range and dereferenceof_or_null is good > for? I haven't checked how the latter is used in detail, but I'm pretty > confident that we don't use call-site parameter range information for > anything.
I see this a little differently. As a general principal, I think we should be doing our best to make our transforms preserve as much information as possible. It seems fine to drop something like `nofree` that isn't entirely well-defined, because we don't actually know what we are preserving yet, but something like `dereferenceable_or_null` is well defined and its not a great stretch of the imagination that the information may be useful somewhere in LLVM or in a downstream project. On the point of `dereferenceable_or_null`, I'd say if `dereferenceable` is considered useful, `dereferenceable_or_null` is also useful by, at the very least, its a potential `dereferenceable` if at any point in the future we can prove the pointer is non-null (and it's hard to argue we have ruled this out by now as inlining generally opens up a lot of new analysis). https://github.com/llvm/llvm-project/pull/91101 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
