[llvm] r202304 - Add a limit to the heuristic that register allocates instructions in local order.

[Andrew Trick]

On Feb 27, 2014, at 11:57 AM, Renato Golin <renato.golin at linaro.org> wrote:

> On 27 February 2014 19:36, Andrew Trick <atrick at apple.com> wrote:
>> - A bug in the host compiler on that builder.
> 
> I'm using Ubuntu's own 4.8.1, which has been working for months. I
> think the chances of the compiler being bad are pretty slim.
> 
> What kind of LNT runs do you do on ARM? Is it Darwin only?
> 
> 
>> - A recent bug in CodeGen that has been hidden by that heuristic and is now exposed.
> 
> I believe this one is the one we should look for. It fails at -O3
> only, so it's probably something that a new optimization is doing and
> the old heuristics can't cope with.
> 
> I did a quick debug session and it failed on something that I remember
> seeing last year. The same problem, and it was magically fixed, and if
> memory serves me well, it was a register allocation commit that "fixed
> it", it might just as well be yours...
> 
> 
>> Reverting would certainly only hide whatever the issue is.
> 
> Agree.
> 
> 
>> 3. I can temporarily disable this change on armv7 using a target hook and file a PR.
> 
> If you could have a look at it on an ARM/Linux, we don't need to
> disable it temporarily. But Linaro Connect will start this weekend and
> will take a whole next week, and I won't be able to look at it until
> the other Monday. When I do start, it'll take a while before I can
> find out where it's breaking, and get a closer idea of how to fix it.
> 
> If not, I think we should disable on ARM, create a PR and assign it to me.
> 
> Makes sense?

Makes sense. PR18996, and workaround in r202433. Let’s hope that fixes the tester.

I wasn’t able to find any record of this failing earlier, but probably didn’t save the emails.

Thanks for all you help.
-Andy

> 
> cheers,
> --renato