llvm dev - Oct 2015 - Should I worry about test failures in a release?

On 13 October 2015 at 13:45, Kuperstein, Michael M via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> As far as I know, the consensus was that all 3.x versions should retain
> backward compatibility for bitcode.
Emphasis on "should". :)

I don't think we have enough tests to make sure we don't break that
promise, precisely because it's important, but not crucial.

> So, 3.7 should be able to consume bitcode (but not text IR) produced by any
> earlier 3.x. When 4.0 rolls around, all bets are off.
And not the other way around, either.

> Note that “consume” here is a not as strong a guarantee as it may sound,
> since metadata may be stripped off. Debug metadata almost certainly will
be.
Yup.

--renato

There's a bunch of tests that make sure at least basic IR constructs from
LLVM 3.2 are still handled correctly.
In addition, this is something that we *used* to test internally, rather more
thoroughly. I'm not sure whether it's still being tested by anyone,
unfortunately.

In any case, if this promise gets broken, it's a bug, not a feature. :-)

-----Original Message-----
From: Renato Golin [mailto:renato.golin at linaro.org] 
Sent: Tuesday, October 13, 2015 15:51
To: Kuperstein, Michael M
Cc: mats petersson; Joachim Durchholz; llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] Should I worry about test failures in a release?

On 13 October 2015 at 13:45, Kuperstein, Michael M via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> As far as I know, the consensus was that all 3.x versions should 
> retain backward compatibility for bitcode.
Emphasis on "should". :)

I don't think we have enough tests to make sure we don't break that
promise, precisely because it's important, but not crucial.

> So, 3.7 should be able to consume bitcode (but not text IR) produced 
> by any earlier 3.x. When 4.0 rolls around, all bets are off.
And not the other way around, either.

> Note that “consume” here is a not as strong a guarantee as it may 
> sound, since metadata may be stripped off. Debug metadata almost certainly
will be.
Yup.

--renato
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On 13 October 2015 at 13:59, Kuperstein, Michael M
<michael.m.kuperstein at intel.com> wrote:
> In any case, if this promise gets broken, it's a bug, not a feature.
:-)
Indeed!

--renato