[llvm-dev] Self-hosting bots noise

[Renato Golin via llvm-dev]

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.

At hindsight, it's obvious. But I hadn't connected the dots before... :/

I'm moving all my self-hosting bots to clean builds and will be
relying solely on ccache to make stage1 fast. This shall help with
"breakages not on the blame list" problems.

cheers,
--renato