2.2. Version 9.6.2

The significant changes to the various parts of the compiler are listed below. See the migration guide on the GHC Wiki for specific guidance on migrating programs to this release.

The LLVM backend of this release is to be used with LLVM 11, 12, 13, 14 or 15.

  • A simplifier bug resulting in compiler crashes in some situations involving rules has been fixed.
  • Several issues affecting the bytecode interpreter’s handling of optimised programs have been fixed (#23068, #22958)
  • A specialisation bug resulting looping of some programs involving non-trivial chains of instances (namely, requiring UndecidableInstances) has been fixed (#22549)
  • A bug resulting in crashes of programs using the new listThreads# primop has been fixed (#23071).
  • A compiler crash triggered by certain uses of quantified constraints has been fixed (#23171)
  • Various bugs in the Javascript backend have been fixed (#23399, #23360, #23346)
  • The non-moving garbage collector’s treatment of weak pointers has been revamped which should allow more reliable finalization of Weak# closures (#22327)
  • The non-moving garbage collector now bounds the amount of marking it will do during the post-marking stop-the-world phase, greatly reducing tail latencies in some programs (#22929)
  • A missing write barrier in the non-moving collector’s handling of selector thunks has been fixed (#22930).

2.2.1. Included libraries

The package database provided with this distribution also contains a number of packages other than GHC itself. See the changelogs provided with these packages for further change information.