On Jun 14, 2016, at 1:32 AM, Richard Smith via cfe-dev <cfe-...@lists.llvm.org> wrote: > I think that this is the right approach, and we happen to have a natural > forcing function here: opaque pointer types. I think we should increment the > major version number when opaque pointer types are here, as it will be a > major breaking change, and then we'll have a version 4.0. Until then, unless > something else breaking comes up, 3.10 sounds fine to me. > > We're talking about version numbers for the entire LLVM project here, which > encompasses a lot more than LLVM IR, and for many parts of which LLVM IR is > utterly irrelevant. I'm not convinced that tying version numbers to > backwards-incompatible changes to IR is reasonable any more, and it doesn't > seem hard to explicitly document the oldest version with which we are > compatible (in fact, we need to do that regardless, whether we say it's "the > same major version" or "everything since 3.0" or whatever else). > > Given that our releases are time-based rather than feature-based, I don't see > a distinct major / minor version being anything other than arbitrary, so I'd > suggest we take 4.0 as our next release, 4.1 as the first patch release on > that, 5.0 as the next release after that, and so on.
I completely agree with Richard here. “Breaking of IR compatibility” was an interesting metric for older and less mature versions of LLVM. We can solve the same sort of challenge (the desire to eject old autoupgrade code) by having a sliding window of versions supported (e.g. version 4.5 supports back to version 3.6). -Chris
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