[cfe-dev] [LLVMdev] Proposal to add Bitcode version field to bitcode file wrapper

[Renato Golin]

On 29 September 2014 15:16, Robinson, Paul
<Paul_Robinson at playstation.sony.com> wrote:
> That promise is what I understood from a discussion within the past month,
> e.g. http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-September/076815.html
> If I misunderstood, clarification on the clarification would be helpful. ;-)

I see, I missed that one. My concerns seem to be similar to Bob's,
though in the past, when we discussed the same topic, there was one
major hurdle to implement that: we'd have to know what features we
removed / stopped supporting and warn on what version brackets
supported that feature. This can only grow as the compiler ages.

Enforcing backwards compatibility with only the major version created
another hurdle: we'd only be able to deprecate bad/temporary features
every few years, creating another bag of legacy. Warnings can be made,
and deprecation of whole sets of features will happen at major
version, which will stress the release validation and increase the
influx of bugs on all major releases.

Whenever I think of any of that, I remember Chris' words: "LLVM IR is
a compiler IR. Nothing more, nothing less". I don't think we should
try to standardise that too much.

My tuppence.

--renato