[llvm-dev] large slowdown in DAGCombiner::MergeConsecutiveStores

[Florian Hahn via llvm-dev]

Hi,

> On Mar 20, 2020, at 18:58, Jeff Bezanson <jeff.bezanson at gmail.com> wrote:
> 
> Thanks for those references. I tried this with a ~1 week old master and indeed the situation is much better. It's now about 2x slower than 6.0.1. The extra time is still in MergeConsecutiveStores. Do you think there's any scope for further limiting the work done there? The performance is now at least tolerable though.

IIRC there is a lot of redundant work done in MergeConsecutiveStores & co. The patches mentioned earlier improved things a bit, but there is definitely more potential for improvements, e.g. by better caching things. 

As a first step, it would be helpful if you could create a bug report with the IR that causes a lot of time spent in MergeConsecutiveStores.

Cheers,
Florian