[llvm-dev] LLVM bc converter from LLVM 3.9 to LLVM 3.1

[Hans Wennborg via llvm-dev]

On Tue, Aug 2, 2016 at 8:44 PM, Mehdi Amini via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
> On Aug 2, 2016, at 8:38 PM, Stephen Hines via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>
> Hi Hongbin,
>
> On Tue, Aug 2, 2016 at 8:26 PM, Hongbin Zheng <etherzhhb at gmail.com> wrote:
>>
>> Hi Steve,
>>
>> Several people told me that LLVM TOT bcreader can read odder version of
>> bitcode without any problem. Do you know the oldest version of bitcode that
>> the TOT bitcode reader supports?
>
>
> The current policy is that LLVM can read bitcode for any prior version with
> the same major version number. Thus 3.9svn can read all the way back to 3.0
> (and also 3.1/3.2/...). It cannot read 2.9 or earlier bitcode. It was also
> policy that the next major release (but only the .0 version) will be able to
> read the prior version of bitcode too. Thus 4.0 is expected to read 3.x
> bitcode as well. 4.1 is not expected to read 3.x bitcode, and it will be an
> error to try to do so. With the new shift to version numbering (i.e. major
> versions are coming out faster - check the recent archives here), I am not
> sure how reliable bitcode will be as a storage format. This is something
> that the RenderScript team is also planning for, since 4.0 will be the last
> supported release that can easily read the 3.2 IR that we currently
> generate.
>
>
> No this is not the current situation: with the version numbering change, the
> policy changed as well. The new and current policy is: we support bitcode
> since 3.0 till we changed our mind.
> Note also that LLVM 4.1 will be a minor “patch” release (like 3.8.1), you
> can expect LLVM 5.0 to be released ~6 months after LLVM 4.0.

Minor point: the patch release after 4.0 will be 4.0.1, to try to
avoid confusion about what kind of release it is.