[llvm-dev] Self-hosting bots noise

Reid Kleckner via llvm-dev
Mon, 09 Nov 2015 18:27:42 -0000

On Mon, Nov 9, 2015 at 8:53 AM, James Y Knight via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> On Nov 9, 2015, at 11:42 AM, David Blaikie via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>
>
> On Mon, Nov 9, 2015 at 4:32 AM, Renato Golin <renato.golin at
linaro.org>
> wrote:
>
>> Hi David/Galina,
>>
>> FYI, I found one big reason why self-hosting bots fail long after the
>> offending commit is tested: dirty builds.
>>
>> In a dirty build (no make clean), when a file X is changed that breaks
>> file Y, the bot will only accuse the failure when file Y is changed,
>> too, so that stage1 with modified X will compile file Y, and break.
>>
>
> That sounds like a bug in the build system - do you have any examples of
> this? We should fix them.
>
> The build should be reliable - any case where a clean build produces a
> different result from a dirty build reduces/removes confidence in
> incremental builds & hurts developer productivity (just like flakey
tests,
> etc).
>
>
> I think he meant that the /second-stage/ build should always be done as a
> clean build -- to make sure that all of the source gets rebuilt with the
> newly-compiled compiler, instead of only rebuilding the modified sources
> with the newly-built compiler.
>
> Build systems typically aren't expected to watch out for the compiler
> itself changing out from under them.
>

+1, I know that my self-hosting Windows buildbot does not do a clean second
stage build, and I've been meaning to fix that for some time.

Renato, I would rather fix this in our buildbot configs. We should just
make stage2 always be clean, and that will fix my builders as well as yours.
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