[TESTING]: ClangBSD branch needs testing before the import to HEAD

[Robert Watson]

On Mon, 31 May 2010, Scott Long wrote:

> On May 31, 2010, at 3:56 AM, Kostik Belousov wrote:
>>
>> My personal opinion is that pushing the import now at the present state of 
>> clang makes a disservice to FreeBSD, and possible clang. Why not keep the 
>> glue on the branch as it is ? Motivated testers willing to help definitely 
>> can checkout from the branch. Import can happen when we are satisfied with 
>> the quality of new compiler, instead of discontent about old one.
>
> Who is "we", and what is their criteria?  Are you speaking for the entire 
> FreeBSD project?

I think Kostik's question here is legitimate: clang maturity changes over 
time.  The earlier we adopt it, the sooner we get the advantages of clang -- 
but we also end up being the people who fault in more of the hard-to-diagnose 
compiler bugs.  Since Kostik fields many of our complex file system/VM/etc 
bugs, which are themselves often symptoms of hardware problems rather than 
software bugs (a similar class of issue), and is on the release engineering 
team, I think he speaks with some authority on the matter.

I happen to (currently) disagree with him on whether clang is ready for us to 
drop in the base system, as I feel providing early access to it (but not 
enabling it as the bootstrap by default) will be of significant benefit, but 
don't think that delegitimizes the concern he raises.  You can burn a lot of 
hours chasing software bugs only to eventually (or never) figure out they are 
compiler bugs.

This is the trade-off, but as you point out in your e-mail, there is also a 
larger non-technical context.  By throwing our weight behind clang, we benefit 
in numerous and often non-technical ways: we lend the clang folks an engaged 
and technically astute user community who can help them mature their software, 
as well as give them a user they community they can point at as part of 
establishing their own legitimacy.  That engagement in turn means they will be 
more responsive to our needs, and it's clear we're at a swing of the 
compiler/systems pendulum where we can benefit from the improved compiler 
technology we get through using clang.

I also have to say that I've found the clang folks extremely responsive to 
date -- the one compiler bug I ran into doing the GCD port to FreeBSD was 
fielded in about 60 minutes, from my report to a fix in their tree.  Very 
impressive.  Of course, I also burned 4-6 hours realizing it was a compiler 
bug before we got to that point, which is, of course, precisely the issue 
Kostik is pushing on.  But I think, at this moment, it's a risk we need to 
take, manage it well, and benefit from the results.

Robert