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Created by Artyom Kuznetsov@hithroc

Compile time regression in GHC 8.10.1

Summary

The module in the code snippet below compiles in about 2.4s on my machine with GHC 8.8.2 and in about 481.76s with GHC 8.10.1. However, if you remove either -Weverything or StrictData from it the compile time will get back to normal. I spent some time bisecting and identified that the following commit causes the issue: c5d888d4 (@sgraf812)

Steps to reproduce

  1. Compile this code snippet with GHC 8.10.1.
  2. Measure the compilation time.

Expected behavior

The code should not take 8 minutes to compile.

Environment

  • GHC version used: 8.10.1

Optional:

  • Operating System: NixOS 20.03
  • System Architecture: x64_86
Edited by Artyom Kuznetsov