.. _release-9-10-1:

Version 9.10.2
==============
The significant changes to the various parts of the compiler are listed in the
following sections. See the `migration guide
<https://gitlab.haskell.org/ghc/ghc/-/wikis/migration/9.10>`_ on the GHC Wiki
for specific guidance on migrating programs to this release.

Language
~~~~~~~~



Compiler
~~~~~~~~

- Optimized lowering of BigNat# literals. ((:ghc-ticket:`23942`), !12179)

- Fixed a bug where the jump shortcutting optimization could lead to unsoundness in pattern matching. ((:ghc-ticket:`24507`))

- Look for haskell symbols only in relevant libraries. ((:ghc-ticket:`23415`))

  When dynamically loading a Haskell symbol (typical when running a splice or
  GHCi expression), before this change we would search for the symbol in
  all dynamic libraries that were loaded. However, this could be very
  inefficient when too many packages are loaded (which can happen if there are
  many package dependencies) because the time to lookup the would be
  linear in the number of packages loaded.

  In one measurement, this improved performance for executing a GHCi expression
  from ~38 seconds down to ~2s.

- Fixed a bug that could cause a linker error when `TypeData` and `StrictData`
  where used in combination. ((:ghc-ticket:`24620`))

- The flag :ghc-flag:`-fprof-late` when combined with `-prof` will no longer prevent top level
  constructors from being statically allocated.

  It used to be the case that we would add a cost centre for bindings like `foo = Just bar`.
  This turned the binding into a caf that would allocate the constructor on first evaluation.

  However without the cost centre `foo` can be allocated at compile time. This reduces code-bloat and
  reduces overhead for short-running applications.

  The tradeoff is that calling `whoCreated` on top level value definitions like `foo` will be less informative.

- IPE profiling - optimize the representation of some internal representations. Leading to smaller executables. ((:ghc-ticket:`24504`))

- Fixed an issue where `-Wmissing-home-modules` caused quadratic compile time increases. ((:ghc-ticket:`24778`))

- Fixed a crash when using `-prof` with `-forig-thunk-info`. ((:ghc-ticket:`24809`))

- Better type inference in certain situations. ((:ghc-ticket:`24810`))

- Fixed a bug where the magic `inline` function sometimes failed to inline functions
  if there were coercions involved. ((:ghc-ticket:`24808`))

- Fixed a bug where the simplifier sometimes destroyed join points during float out. ((:ghc-ticket:`24768`))

- PPC NCG: Fix sign hints in C calls. This bug caused segfaults when using FFI under some
  circumstances. ((:ghc-ticket:`23034`))

- Fixed a bug that caused GHC to panic when using the aarch64 ncg and -fregs-graph
  on certain programs. ((:ghc-ticket:`24941`))

- The flag :ghc-flag:`-fkeep-auto-rules` that forces GHC to keep auto generated
  specialization rules was added. It was actually added ghc-9.10.1 already but
  mistakenly not mentioned in the 9.10.1 changelog.

- Fixed re-exports of ``MkSolo`` (:ghc-ticket:`25182`)

- Fixed the behavior of ``Language.Haskell.TH.mkName "FUN"`` (:ghc-ticket:`25174`)

- Various code generation improvements to the ARM backend.

- Fixed a bug that could case segfaults in GHCi when `-fworker-wrapper-cbv` was enabled. ((:ghc-ticket:`24870`))

- Fixed a correctness issues for Int64/Word64 on 32bit backends ((:ghc-ticket:`24893`))

- Various rts linker improvements:
  - R_X86_64_PC64 relocation support on windows
  - Use m32 allocator for sections when NEED_PLT - works around ((:ghc-ticket:`24432`))
  - AArch64 - Skip NONE relocations

- AArch64 ncg: Multiway branches are now lowered to jump tables for better performance. ((:ghc-ticket:`19912`))

- Fixes related to better use of sse4 when using the llvm backend:
  - Use +sse4.2 rather than +sse42, fixing ((:ghc-ticket:`25019`)),
  - make SSE4.2 imply +popcnt, fixing ((:ghc-ticket:`25353`)).

- Fixed a bug where the use of ``throw`` caused a loss of strictness ((:ghc-ticket:`25066`)).

- Fixed incorrect behaviour that could occur when using ``control0#/prompt#`` ((:ghc-ticket:`25439`)) by making `prompt#` lazy.

- Fixed a bug where ghc paniced during type checking. ((:ghc-ticket:`25325`))

- Fix linearity for strict unit patterns in a local let bindings. ((:ghc-ticket:`25428`))

- Improve the performance of type family consistency checks. ((:ghc-ticket:`25554`))

- Fixed a bug where type checking failed to terminate. ((:ghc-ticket:`25597`))

- Fixed a bug where ``__GLASGOW_HASKELL_LLVM__`` was not defined even if `-fllvm` was set. ((:ghc-ticket:`25606`))

- Added flags to control speculative evaluation: ``-fspec-eval`` and ``-fspec-eval-dictfun``. This allows
  users to work around cases where recent changes to speculative evaluation caused performance regressions. ((:ghc-ticket:`25606`))

JavaScript backend
~~~~~~~~~~~~~~~~~~

- Changes for better support of the Google Closure Compiler ((:ghc-ticket:`24602`), !12330)

- JS Backend: support rubbish static literals

- Fix h$withCStringOnHeap helper ((:ghc-ticket:`25288`))

WebAssembly backend
~~~~~~~~~~~~~~~~~~~

- wasm: use scheduler.postTask() for context switch when available

- The in tree gmp library now is configured to produce faster and smaller code given
  the current constraints of the wasm backend. (!12592)

GHCi
~~~~

- When using XDG directories ``.ghci_history`` now uses the ``$XDG_DATA_HOME`` variable as expected. ((:ghc-ticket:`24266`))

- Replaced some uses of lists with Arrays for better performance during bytecode compilation.

- GHCi: support cross-module inlining of breakpoints. Fixing (:ghc-ticket:`24712`)

- Fix a bug where GHCi would not start alongside a local file called ``Prelude.hs``
  or ``Prelude.lhs`` (:ghc-ticket:`10920`).

- Fixed a panic in the ghci debugger when using breakpoints around field selectors. ((:ghc-ticket:`25109`))

- Fixed a bug (:ghc-ticket:`25150`) where ghc would not consider ``-working-dir`` when
  looking for foreign files.

Runtime system
~~~~~~~~~~~~~~

- Memory return logic now uses live bytes rather than live blocks to measure the size of the heap.
  This primarily affects the non-moving GC, which should now be more willing to return memory to the OS.
  Users who have fine-tuned the :rts-flag:`-F ⟨factor⟩`, :rts-flag:`-Fd ⟨factor⟩`, or :rts-flag:`-O ⟨size⟩` flags,
  and use the non-moving GC, should see if adjustments are needed in light of this change.

- Reduce fragmentation incurred by the nonmoving GC's segment allocator. In one application this reduced resident set size by 26%. See :ghc-ticket:`24150`.

- Emit warning when -M < -H.

- Fix a bug ((:ghc-ticket:`24672`)) causing programms on FreeBSD to occasionally terminate with the error:
  ``internal error: Ticker: read(timerfd) failed with Operation not supported and returned -1``

- Fixed a bug ((:ghc-ticket:`25503`)) that sometimes caused the rts to terminate with ``internal error: alloc_adjustor_chunk: failed to allocate`` on windows.
  This primarily affect programs making use of the ``foreign import "wrapper"`` functionality.

- Fixed a bug in compacting gc that could result in program termination with ``update_fwd_large: unknown/strange object  38`` ((:ghc-ticket:`24791`)).

- Fixed a bug where calling ``setNumCapabilities`` with a argument larger than 256 caused crashes. (:ghc-ticket:`25560`)

Build system and packaging
~~~~~~~~~~~~~~~~~~~~~~~~~~

- Escape argument strings when storing them in the settings file. Fixes (:ghc-ticket:`24265`)

- Updated autoconf scripts to commit 948ae97ca5703224bd3eada06b7a69f40dd15a02 (dated 2024-01-01).
  (From https://git.savannah.gnu.org/cgit/config.git/)

- GHC now distinguishes more between the Cmm and C preprocessor. The new flags
  `-pgmCmmP` and `-optCmmP` can be used to control
  the Cmm preprocessor. C preprocessor flags will still be passed to the Cmm
  preprocessor, expect for -g flags which have special handling. Fixes (:ghc-ticket:`24474`)

- Bindists: Fixed a bug in the Makefile which caused windows installs to duplicate files. ((:ghc-ticket:`24800`))

- The packages ghc-internal and ghc-experimental are now versioned based on the GHC version they are shipped with.

- Fixed a bug where running ``Xelatex`` concurrently failed. (:ghc-ticket:`25564`)

- Fixed a bug where building ghc from source using ghc-9.8.4 failed with an error mentioning ``ghc_unique_counter64``. (:ghc-ticket:`25576`)

``base`` library
~~~~~~~~~~~~~~~~




``ghc-prim`` library
~~~~~~~~~~~~~~~~~~~~


``ghc`` library
~~~~~~~~~~~~~~~

- Added some utility functions to `GHC.Data.SmallArray`

``ghc-heap`` library
~~~~~~~~~~~~~~~~~~~~

- Fix typo in ghc-heap cbits that caused compilation errors when assertions were enabled.

``ghc-experimental`` library
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* Primops and other ghc extensions are now exported via ``GHC.PrimOps``
* The library is now versioned according to the ghc version it shipped with.


``template-haskell`` library
~~~~~~~~~~~~~~~~~~~~~~~~~~~~


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.
