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

[Florian Hahn via llvm-dev]

Hi,

> On Mar 19, 2020, at 20:29, Jeff Bezanson via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hello all,
> 
> We are seeing a large compiler performance regression in moving from LLVM 6.0.1 to 8.0.1. We have a long function (~50000 instructions) that used to compile in about a minute but now takes at least an hour. All the time is in MergeConsecutiveStores, I believe due to super-linear behavior in analyzing very long chains of stores. For example, this change makes the problem go away:
> 

Are you seeing the same performance regression on master? 

Over the last year, at least 2 patches landed to improve compile time in similar cases: https://reviews.llvm.org/D62633 https://reviews.llvm.org/D65174

Cheers
Florian