How to track down a bad llvm optimization pass

[Joakim via digitalmars-d-ldc]

On Monday, 4 July 2016 at 09:21:19 UTC, Joakim wrote:
> On Saturday, 2 July 2016 at 07:42:31 UTC, Johan Engelen wrote:
>> On Saturday, 2 July 2016 at 07:29:47 UTC, Joakim wrote:
>>> 
>>> I was surprised that llvm is just silently doing this, with 
>>> no warning.
>>
>> This blog article gives some insight:
>> http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_21.html
>
> Thanks for the link, it's very relevant.  I've mentioned these 
> issues and closed the llvm bug as invalid, as that GVN pass was 
> only surfacing this undefined behavior.
>
> Leaving aside the optimizer, the unoptimized phobos debug tests 
> should have caught this, shouldn't they?  I'll look into why 
> those passed next.

Alright, tracked this down, it was a test that had a bad failure 
mode.  I'll write it up in the General forum.

Johan, you mentioned this other shift bug that you ran into:

https://github.com/dlang/phobos/pull/4509

Was that just one that you had hit recently or did you go 
checking all 20+ uses of logical right shift in Phobos to look 
for bugs?