GHC HEAD (Quickest) segfaults during compilation of optparse-applicative

Hello, GHC HEAD (9668781a36941e7552fcec38f6d4e1d5ec3ef6d1) compiled with the Quickest flavour segfaults when compiles optparse-applicative-0.15.1.0. But it compiles fine with the Quick or the default flavours. [image: image.png] Everything compiles fine (with vanilla Quickest GHC HEAD) until the Options.Applicative.Help.Core module where GHC segfaults. (as I understand the error code) Is this a known bug? If not then I'll submit an issue. Thanks, Csaba