[llvm-dev] RFC: Building GlobalISel by default

Renato Golin via llvm-dev
Sat, 14 Jan 2017 19:32:30 -0000

On 14 January 2017 at 18:53, Mehdi Amini <mehdi.amini at apple.com>
wrote:
> I don’t see why having global ISel is supposed to increase the rate. `make
check` will runs on the committer machine with GlobalISel enabled.

You assume the environments are the same, so the same bugs will be
caught on an x86 host or on an ARM host. If that was true, than most
of the breakages we have would just not happen.

To make matters worse, if a breakage is unknown to the committer (ie,
due to some GISel idiosyncrasy), the committer will not worry about it
and will leave the bot red, which increases the load on bot
maintainers.


> But that’s totally unrelated to the bots, since it’ll fails on the
committer machine as well.

If that's unrelated, than why is it a plus that we have all other
buildbots building it instead of just the one Apple has it already?


> This is *not* about enabling GlobalISel  *by default* on any target AFAIK.

I got that. That is a second step, for later. My point is that, if a
feature is not good enough to be used anywhere, then it can remain as
experimental, since the cost is just adding a flag to enable the
back-end.

I can easily do that on one of my bots, just for that purpose, but I
wouldn't feel comfortable doing that to all my bots at once (or having
to use special flags to remove experimental features).

--renato