[llvm-dev] Why does new llvm-as reject old IR format?

[James Y Knight via llvm-dev]

On Fri, Aug 12, 2016 at 10:05 AM, Madhur Amilkanthwar via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Surprised to know that backward compatibility is not honored across the
> tools.
> (i.e. you can read old .bc but NOT old .ll files)
> Supporting latter is more useful, IMO, because then I wouldn't have to
> modify all my sources.
>

It's been that way for LLVM's entire existence. One could imagine ways to
allow for source-level IR compatibility as well, but, at the moment there
isn't any such promise.

See:
http://llvm.org/docs/DeveloperPolicy.html#ir-backwards-compatibility

And who are "we" here?
>

"We" is the LLVM community, since that is the official policy of the LLVM
project.


>  On Fri, Aug 12, 2016 at 7:21 PM, Tim Northover <t.p.northover at gmail.com>
> wrote:
>
On 12 August 2016 at 06:42, Madhur Amilkanthwar via llvm-dev
>> <llvm-dev at lists.llvm.org> wrote:
>> > Ideally, I would expect backward compatibility from LLVM tools; and not
>> > requiring to modify the code again.
>> >
>> > What is LLVM's philosophy here?
>>
>> We support backwards compatibility (i.e. newer tools can read older
>> files) on .bc files but not .ll files. This goes back to version 3.0
>> so nothing new can read files from the 2.9 or earlier era and the
>> other direction (older tools reading newer files) is never going to
>> work.
>>
>> We're in the middle of changing our version numbering and official
>> policy, but the general sense is that we have no intent to break this.
>>
>> So for your particular problem you should be able to use a 3.2 llvm-as
>> and then do what you like with the .bc file.
>>
>> Cheers.
>>
>> Tim.
>>
>
>
>
> --
> *Disclaimer: Views, concerns, thoughts, questions, ideas expressed in this
> mail are of my own and my employer has no take in it. *
> Thank You.
> Madhur D. Amilkanthwar
>
>
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