ghc 8.8.3 with llvm 9, instead of 8.6.5 with llvm 6 sometimes OOM on arm

In Ubuntu we are currently upgrading from 8.6.5 to 8.8.3 Before llvm 6 was used on arm architectures, but now llvm 9 is.

We are observing packages that used to build fine, now get killed during build by the OOM killer when trying to build optimized builds of haskell packages. For example, pandoc.

Disabling optimization make the build succeed.

It's hard to tell, if this is a regression in llvm, ghc, or Ubuntu. But i thought it might be worth mentioning.