How to track down a bad llvm optimization pass

[Joakim via digitalmars-d-ldc]

On Sunday, 19 June 2016 at 06:45:42 UTC, Dan Olson wrote:
> Dan Olson <gorox at comcast.net> writes:
>
>> Joakim <dlang at joakim.fea.st> writes:
>>
>>> On Saturday, 18 June 2016 at 15:31:03 UTC, Joakim wrote:
>>> I just built and linked against llvm 3.7.1 and the problem 
>>> goes away,
>>> so it appears that it is a regression in the GVN optimization 
>>> pass
>>> with llvm 3.8.0.  I'll check if it goes away with llvm 
>>> master, and
>>> file an llvm bug if it doesn't.
>>
>> And I am trying opposite: builting ldc master against llvm 
>> 3.8.0.  See if I can duplicate the problem.
>
> Yup, fails same way on a Raspberry Pi with 3.8.0.

And it's still hitting on llvm 3.9 master svn-271934 from a 
couple weeks ago, looks like we'll have to submit a bug report.  
Anyone know if we're breaking some llvm assumptions here?