GitLab

Duncan Coutts pushed to branch wip/dcoutts/issue-27086-wakeUpRts at Glasgow Haskell Compiler / GHC

Commits:

44cf9cd7
by Wolfgang Jeltsch at 2026-05-12T09:48:18-04:00
```
Move the `Text.Read` implementation into `base`
```

4ac3f7d6

by Vladislav Zavialov at 2026-05-12T09:49:03-04:00

EPA: Use AnnParen for tuples and sums

Summary of changes

* Do not use AnnParen in XListTy, replace it with EpToken "[" and "]"
* Specialise AnnParen to tuple/sums by dropping the AnnParensSquare
  and keeping only AnnParens and AnnParensHash
* Use AnnParen in XExplicitTuple
* Use AnnParen in XExplicitTupleTy
* Use AnnParen in XTuplePat
* Use AnnParen in XExplicitSum (via AnnExplicitSum)
* Use AnnParen in XSumPat (via EpAnnSumPat)

This is a refactoring with no user-facing changes.

1bdcddec

by Duncan Coutts at 2026-05-12T09:49:48-04:00

Add minimal dlltool support to ghc-toolchain

The dlltool is a tool that can create dll import libraries from .def
files. These .def files list the exported symbols of dlls. Its somewhat
like gnu linker scripts, but more limited.

We will need dlltool to build the rts and ghc-internal libraries as DLLs
on Windows. The rts and ghc-internal libraries have a recursive
dependency on each other. Import libraries can be used to resolve
recursive dependencies between dlls. We will use an import library for
the rts when linking the ghc-internal library.

f7fc3770

by Duncan Coutts at 2026-05-12T09:49:48-04:00

Add minimal dlltool support into ./configure

Find dlltool, and hopefully support finding it within the bundled llvm
toolchain on windows.

e4e22bfb

by Duncan Coutts at 2026-05-12T09:49:48-04:00

Update the default host and target files for dlltool support

5666c8f9

by Duncan Coutts at 2026-05-12T09:49:48-04:00

Add dlltool as a hadrian builder

Optional except on windows.

5e14fe3f

by Duncan Coutts at 2026-05-12T09:49:48-04:00

Update and generate libHSghc-internal.def from .def.in file

The only symbol that the rts imports from the ghc-internal package now
is init_ghc_hs_iface. So the rts only needs an import lib that defines
that one symbol.

Also, remove the libHSghc-prim.def because it is redundant. The rts no
longer imports anything from ghc-prim.

Keep libHSffi.def for now. We may yet need it once it is clear how
libffi is going to be built/used for ghc.

3d91e4a6

by Duncan Coutts at 2026-05-12T09:49:48-04:00

Add rule to build libHSghc-internal.dll.a and link into the rts

On windows only, with dynamic linking.

This is needed because on windows, all symbols in dlls must be resolved.
No dangling symbols allowed. References to external symbols must be
explicit. We resolve this with an import library. We create an import
library for ghc-internal, a .dll.a file. This is a static archive
containing .o files that define the symbols we need, and crucially have
".idata" sections that specifies the symbols the dll imports and from
where.

Note that we do not install this libHSghc-internal.dll.a, and it does
not need to list all the symbols exported by that package. We create a
special purpose import lib and only use it when linking the rts dll, so
it only has to list the symbols that the rts uses from ghc-internal
(which is exactly one symbol: init_ghc_hs_iface).

c8dae539

by Alice Rixte at 2026-05-12T09:50:52-04:00

Script for downloading and copying `base-exports` file

5fab2238

by Wolfgang Jeltsch at 2026-05-12T21:24:27+03:00

Introduce a cache of home module name providers

This contribution introduces to the module graph a cache that maps home
module names to sets of units providing them and changes the finder to
use that cache. This is a performance optimization, especially for
multi-home-unit builds.

The particular changes are as follows:

  * In `GHC.Unit.Module.Graph`, `ModuleGraph` is extended with a new
    field `mg_home_module_name_providers_map`, exposed as
    `mgHomeModuleNameProvidersMap`. This is a cache that assigns to each
    home module name the set of IDs of home units that define it.
    Operations that construct module graphs are updated such that this
    cache stays synchronized.

  * In `GHC.Unit.Finder`, `findImportedModule` is changed to pull
    `mgHomeModuleNameProvidersMap` from `hsc_mod_graph` and pass it to
    `findImportedModuleNoHsc`, which now does not search home units in
    arbitrary order but prioritizes those units that the cache mentions
    as potential providers of the requested module.

In addition, this contribution adds variants of the two multi-component
compiler performance tests that use 100 units instead of 20, because
with just 20 units the benefits from caching of home module name
providers are still negligible.

The following table shows the total time needed for running both
multi-component tests before and after this contribution and with
different numbers of units:

| # of units | Before | After |
|-----------:|-------:|------:|
|         20 |   0:12 |  0:12 |
|        100 |   0:47 |  0:42 |
|        200 |   3:05 |  2:08 |

Note that there seems to be a general overhead of 12 seconds that is not
attributable to the actual tests, so that the real running times should
be 12 seconds smaller than shown above.

Resolves #27055.

Metric Decrease:
    MultiComponentModules
    MultiComponentModulesRecomp

Co-authored-by: Matthew Pickering <matthewtpickering@gmail.com>
Co-authored-by: Fendor <fendor@posteo.de>

38b76b2f

by Cheng Shao at 2026-05-13T17:48:48-04:00

testsuite: mark T22159 as fragile

This patch marks T22159 as fragile on Windows for issue described in #27248.
Before we get to the bottom of those failures, this unblocks newer
Windows runners.

50188615

by Ian Duncan at 2026-05-14T13:45:07+02:00

AArch64: use ASR not LSR for MO_U_Shr at W8/W16

The unsigned right shift (MO_U_Shr) for sub-word widths (W8, W16)
with a variable shift amount was emitting ASR (arithmetic/signed shift
right) after zero-extending with UXTB/UXTH. This should be LSR
(logical/unsigned shift right). After zero-extension the upper bits
happen to be 0 so ASR produces the same result, but it is semantically
wrong and would break if the zero-extension were ever optimized away.
Includes assembly output test (grep for lsr) and runtime test
verifying unsigned right shift of Word8 and Word16 values.

28666fbf

by Vladislav Zavialov at 2026-05-19T12:44:05-04:00

Add type families: Tuple, Constraints, Tuple#, Sum# (#27179)

These type families map tuples of types to the corresponding Tuple<N>,
Tuple<N>#, CTuple<N>, and Sum<N># types. Some examples at N=2:

	Tuple (Int, Bool)          = Tuple2 Int Bool
	Constraints (Show a, Eq a) = CTuple2 (Show a) (Eq a)
	Tuple# (Int#, Float#)      = Tuple2# Int# Float#
	Sum# (Int#, Float#)        = Sum2# Int# Float#

See GHC Proposal #145 "Non-punning list and tuple syntax".

To make the Sum# instance at N=64 possible, this patch also introduces
the Sum64# constructor declaration and bumps mAX_SUM_SIZE from 63 to 64.

Metric Increase:
    ghc_experimental_dir

41c2448b

by Wen Kokke at 2026-05-19T12:44:53-04:00

rts: Add IPE event class for -l

This commit adds a new IPE event class to the -l RTS flag.
Previously, IPE events were enabled unconditionally.
However, the IPE events can easily grow to hundreds or thousands of megabytes.
With the new event class you can pass, e.g., -l-I to disable IPE events.

62536551
by Wen Kokke at 2026-05-19T12:44:53-04:00
```
ghc-internal: Add TraceFlags.traceIPE
```
e45312d1
by Wen Kokke at 2026-05-19T12:44:53-04:00
```
testsuite: Add test for TraceFlags.traceIpe
```
4768d9aa
by Wen Kokke at 2026-05-19T12:44:53-04:00
```
ghc-internal: Add DebugFlags.ipe
```
bc1b5c69
by Wen Kokke at 2026-05-19T12:44:53-04:00
```
testsuite: Add test for DebugFlags.ipe
```

0da1543f

by Duncan Coutts at 2026-05-19T12:45:37-04:00

Document removal of the signal-based interval timer

Update mentions within the RTS section of the users guide.

Add a changelog entry.

b2911514
by Duncan Coutts at 2026-05-19T12:45:37-04:00
```
Fix section for an recent changelog entry
```

d6d76a7a

by David Eichmann at 2026-05-19T12:46:19-04:00

ghc-toolchain: implement llvm program versioning logic

2dd36fa3

by Wolfgang Jeltsch at 2026-05-20T04:49:52-04:00

Turn `Trustworthy` into `Safe` in `base` where possible

f4399dd1
by Wolfgang Jeltsch at 2026-05-20T04:50:37-04:00
```
Make the current `base` buildable with GHC 10.0
```

1a7de232

by Duncan Coutts at 2026-05-20T12:26:25-04:00

Hadrian: remove legacy rts .so symlinks

For compatibility with the old makefile based build system, hadrian had
rules to generate symlinks from unversioned to versioned names for the
rts .so/.dynlib file, like libHSrts-ghcx.y.so -> libHSrts-1.0.3-ghcx.y.so

We no longer need these symlinks since the makefile build system has
been retired some time ago. The need for these symlinks is awkward on
windows where we cannot (in practice) create symlinks. So rather than
make them conditional (non-windows), just remove them entirely.

286f1adf

by fendor at 2026-05-20T12:27:09-04:00

Fix regression T27202: `:load` and `:add` work in GHCi

To fix the regression there are conceptually two major things that we
fix:

* We don't remove the `importDirs` from `interactive-session`
* When `:add`ing a module, we don't try to find them via PackageImports
    * The PackageImport is wrong as we can't know the package-name at
      this stage in ghc/UI.hs

What does it mean to not remove the `importDirs` from
`interactive-session`?
It means that, given some initial `DynFlags`, we will use those
`importDirs` in `interactive-session`.

The initial `DynFlags`, however, depend on how you initialise the GHC
session.
For a simple session, initialised by

    ghc -isrc -this-unit-id main

It is simple, just use the `DynFlags` given on the cli.
Thus, `main` and `interactive-session` will have the same `DynFlags`,
except for the `homeUnitId` and `interactive-session` depends on `main`
by construction of the GHCi session.

What about a multiple home unit session, though?

    ghc -unit @unit1 -unit @unit2

What are the `DynFlags` in this cli invocation? It shouldn't be either
`@unti1` nor `@unit2`, as the order shouldn't matter or any other
implicit condition.

For consistency, we decide that the initial `DynFlags` are the top
`DynFlags` on the cli, ignoring `-unit` flags.
Thus, in this example, there are no `importsDirs` regardless of what we
might find in `@unit1` and `@unit2`.

But in this invocation:

    ghc -isrc -unit @unit1 -unit @unit2

The `interactive-session` will have the `importsDirs` `src`.
Note, `-isrc` will be inherited in `@unit1` and `@unit2`, so you need to
explicitly use `-i` to clear the `importsDirs`, in order to avoid
accidentally adding `src` as an import directory to all other home
units.

This fix has been made possible by the improvements introduced in
!15888, which avoids ambiguity when a home unit shares the `importsDirs`
with the `interactive-session`, on top of being much faster for multiple
home units.

Adds regression tests for T27202 for `:load`ing and `:add`ing modules
that are located in import directories.

728662de

by fendor at 2026-05-20T12:27:09-04:00

Use home unit package db stacks in GHCi prompt and session unit

In order to import modules from home unit dependencies (e.g., `Data.Map`),
the ghci prompt unit needs to populate its `UnitState`.
This is tricky to handle correctly, which `PackageDBFlag`s should we use
to populate the `UnitState`?
We decide, the most intuitive solution for users is to depend on all
`PackageDBFlag`s, so that any dependency can be imported in GHCi.
This assumes consistency in the `PackageDBFlag`s, so no two home units
specify `PackageDBFlag`s that are inconsistent with each other.

We could simply concat all the `PackageDBFlag`s of the existing home
units, but later `PackageDBFlag`s shadow earlier ones, leading to the
last processed home units' `PackageDBFlag`s to shadow the earlier ones.
This is hard to fix, we need to give users the capability to provide ghc
options for the ghci prompt home unit.
However, as this is considerably more work, we decided on an
approximation that should work out most of the time.

Package Db stacks in cabal and stack follow a certain structure:

    -no-user-package-db > -package-db $cabal-store > -package-db $local-db

The first two arguments are always the same, namely the
`-no-user-package-db` and `-package-db`.
We compute the longest common prefix over all home units, and use that
as the start of the package db stack. Then, over the rest of the
`PackageDBFlag`s, we simply take the union and append them to our
initial stack.
We assume, that the rest of package dbs only defines very few, "local"
units that are usually not shadowing each other.

This allows us to get a relatively consistent package database stack for
the ghci prompt home unit.

Similar reasoning applies to the session unit in order to add modules to
the session and have dependencies available in the module.

We do something similar for `-package` flags, to make sure only the
correct units are actually visible in the ghci session.
This time, we simply take the union of all `PackageFlag`s, allowing us
to import modules from the home unit dependencies.

In the future, it would be beneficial to allow the user to provide the
exact ghc options to control the visibilities. For now, this will have
to do.

740d89a0

by Simon Peyton Jones at 2026-05-20T17:20:44-04:00

Do not use mkCast during typechecking

This commit fixes #27219.  The problem was that the typechecker was using
`mkCast`, whose assertion checks legitimately fail when applied to types
that contain unification variables.

a50fdb06

by Simon Peyton Jones at 2026-05-20T17:20:45-04:00

Major refactor of the Simplifier

The main payload of this patch is to refactor the Simplifer to avoid
repeated simplification when using Plan (AFTER) for rule rewrites.
The need for this was shown up by #26989.

See Note [Avoid repeated simplification] in GHC.Core.Opt.Simplify.Iteration.

Related refactoring:

* Refactor the two fields `sc_dup` and `sc_env` in `ApplyToVal` into one, `sc_env`.
  Reason: the envt is irrelevant in the "simplified" case, so the data type describes
  the possiblitiies much more accurately now.

* Some refactoring in `knownCon` to split off `wrapDataConFloats`.

* Refactor `lookupRule` and its auxiliary functions to return `RuleMatch`,
  a new data type. See Note [data RuleMatch] in GHC.Core. Ditto for BuiltinRule.

  This RuleMatch returns fragments of the target in rm_args and rm_floats,
  leaving `rm_rhs` to be the stuff from the RULE itself.

  Doing this has routine consequences in GHC.Core.Opt.ConstantFold. Many changes
  there but all routine.

* When doing occurrence analysis on RULEs, make the occ-info on the rule
  binders relate just to the RHS, not the LHS.  See (OUR1) in
  Note Note [OccInfo in unfoldings and rules]

  This means that Lint must not complain about the fact that the patterns
  in the RULE mentions binders that are marked dead.
  See Note [Dead occurrences] in GHC.Core.Lint.

  I changed the Core pretty-printer so that it didn't suppress dead binders,
  else I can't see those binders in RULEs.  That led to quite a lot of testsuite wibbles.

* Refactor FloatBinds, so that it is used both by
  `exprIsConApp_mabye` and by `lookupRule`
  * Move the definition of FloatBinds out of GHc.Core.Make, into GHC.Core.
  * Add FloatTick as an extra constructor.
  * Refactor `lookupRule` to use `FloatBinds` instead of `BindWrapper`.
  This refactor just shares more code.

  (Rename GHC.Core.Opt.FloatOut.FloatBinds to FloatLets, to avoid gratuitious
  name clash with GHC.Core.FloatBinds.)

Corecion optimisation

* In simpleOpt, when composing coercions, call new function `optTransCo`.
  This is much lighter weight than full blown coercion optimisation.

* Make `GHC.Core.Opt.Arity.pushCoValArg` and `pushCoTyArg` return the
  coercionLKind of the coercion. This saves recomputing that coercionLKind
  at the key call sites in GHC.Core.Opt.Simplify.Iteration.pushCast.

* Rename `addCoerce` in GHC.Core.Simplify.Iteration to become `pushCast`.

* In the `ApplyToVal` case of `pushCast` we had a very unsavoury call to `simplArg`.
  I eliminated it by adding a field `sc_cast` to `ApplyToVal` that records any
  pending casts.  Much nicer now.  See Note [The sc_cast field of ApplyToVal].

* Don't optimise coercions if the type-substitution is empty.
  See Note [Optimising coercions] in GHC.Core.Opt.Simplify.Iteration.

The fix for #26838 is dramatic.  For the test in perf/compiler/T26839 we have

   Compiler allocs:  Before: 7,363M
                     After:    688M

Compile time goes down generally.  Here are compiler-alloc changes
over 0.5%:
           CoOpt_Read(normal)    729,184,920   -0.7%
     CoOpt_Singletons(normal)    666,916,960   -4.6% GOOD
          LargeRecord(normal)  1,227,056,876   +1.1%
               T12227(normal)    256,827,604   -4.6% GOOD
               T12425(optasm)     76,879,410   -0.8%
               T12545(normal)    787,826,918  -10.8% GOOD
               T12707(normal)    775,186,464   -0.9%
               T13253(normal)    318,599,596   -0.8%
               T14766(normal)    685,857,320   -1.0%
               T15304(normal)  1,123,333,422   -2.2%
               T15630(normal)    123,142,330   -2.6%
              T15630a(normal)    123,092,100   -2.6%
               T15703(normal)    299,751,682   -2.9% GOOD
               T17516(normal)    964,072,280   +1.0%
               T18223(normal)    367,016,820   -6.2% GOOD
               T18730(optasm)    130,643,770   -3.3% GOOD
               T20261(normal)    535,608,584   -0.7%
              T21839c(normal)    340,340,436   -0.9%
               T24984(normal)     85,568,392   -1.9%
                T3064(normal)    174,631,992   -1.2%
                T3294(normal)  1,215,886,432   -0.7%
                T5030(normal)    141,449,704  -17.2% GOOD
             T5321Fun(normal)    258,484,744   -1.9%
                T8095(normal)    770,532,232   -2.7%
                T9630(normal)    858,423,408  -14.5% GOOD
               T9872c(normal)  1,591,709,448   +0.7%
  info_table_map_perf(normal) 19,700,614,458   -1.3%

                    geo. mean                  -0.7%
                    minimum                   -17.2%
                    maximum                    +1.1%

However, strangely there seems to be a 5.0% increase in CoOpt_Read in
the x86_64-linux-fedora43-validate+debug_info+ubsan job, although
there generally a /decrease/ in this test in other builds.  The baseline
value looks strange.  Anyway I'll just accept it.

Metric Decrease:
    CoOpt_Singletons
    T12227
    T12545
    T12707
    T15703
    T18223
    T18730
    T21839c
    T5030
    T9630

Metric Increase:
    CoOpt_Read

834623d4

by Mrjtjmn at 2026-05-20T17:21:41-04:00

users-guide: Fix weird notation in "Summary of stolen syntax"

6f9d7c71

by Markus Läll at 2026-05-21T15:25:34-04:00

Use "grimily" instead of "grimly"

Fixes https://gitlab.haskell.org/ghc/ghc/-/issues/27221

50e999ca

by fendor at 2026-05-21T15:26:18-04:00

Speed up 'closure' computation in `ghc-pkg`

Cache the set of already seen `UnitId`s and use `Set` operations to
speed up 'closure' computation.

Further simplify the implementation of 'closure' to account for the
actual usage.
As a consequence, we rename 'closure' to 'brokenPackages' to reflect its
purpose better after the simplification.

7ecc6184

by sheaf at 2026-05-21T15:27:10-04:00

TcMPluginHandling: be more lenient when no plugins

This change ensures that, if a function such as 'typecheckModule' was
invoked with 'NoTcMPlugins', GHC doesn't spuriously complain about TcM
plugins having already been stopped, as there were none to start with.

72c8de5c

by Simon Jakobi at 2026-05-23T18:41:42-04:00

Implement List.elem via foldr

...in order to allow specialization to Eq instances.

The implementation of notElem is updated for consistency.`

Corresponding CLC proposal:
https://github.com/haskell/core-libraries-committee/issues/412

Addresses #27096.

3268c610

by Alan Zimmerman at 2026-05-23T18:42:30-04:00

EPA: Fix span for qualified multiline string

Fix the span for a qualified multiline string like

  Text."""
    I'm a multiline
    Text value
    !
  """

to extend to the end of the entire string, not just the first line.

Closes #27274

1f096790

by Alan Zimmerman at 2026-05-23T18:43:20-04:00

EPA: Fix exact printing namespace-specified wildcards

Ensures correct printing of imports of the form

   import Data.Bool (data True(data ..))
   import Data.Bool (data True(type ..))

Closes #27291

56ada7c0

by Mrjtjmn at 2026-05-23T18:44:19-04:00

Fix ambiguous syntax of BangPatterns in users guide

Update documentation for the BangPatterns extension to specify
how surrounding whitespace affects interpretation of `!`.

* Only when there is whitespace before `!` and no whitespace after,
  it is recognized as a BangPattern.
* Other cases `⟨varid⟩!⟨varid⟩`, `⟨varid⟩ ! ⟨varid⟩`, `⟨varid⟩! ⟨varid⟩`
  are treated as infix operators.

579aa0b7

by Simon Jakobi at 2026-05-25T16:31:26-04:00

Ensure that SetOps.{minusList,unionListsOrd} can be specialized

...by marking them INLINABLE. Haddock allocates 0.1–0.3% less as a
result.

This also removes some redundant constraints on unionListsOrd.

cccf45da

by Cheng Shao at 2026-05-25T16:32:13-04:00

wasm: ensure post-linker output is synchronous ESM

This patch fixes wasm backend's post-linker output script to ensure
it's synchronous ESM and doesn't use top-level await, which doesn't
work in ServiceWorkers. Fixes #27257.

8db331a3

by Zubin Duggal at 2026-05-26T04:54:03-04:00

Update to semaphore-compat 2.0.0 using v2 of the protocol

On Linux and other POSIX platforms, GHC's -jsem jobserver client now
speaks v2 of the semaphore-compat protocol, which uses Unix domain
sockets in place of POSIX named semaphores. This avoids the libc-ABI
issues that affected the old implementation. Windows is unaffected
and continues to use the v1 protocol (Win32 named semaphores); its
reported protocol version remains v1.

When GHC receives a -jsem name whose protocol version it does not
support, it emits a -Wsemaphore-version-mismatch warning and falls
back to -j<N> rather than crashing. ghc --info exposes the supported
version in a new "Semaphore version" entry so cabal-install can detect
a mismatch before invoking GHC.

Users on a cabal-install that predates the v2 update will continue to
build successfully on Linux/POSIX, but will lose the cross-process
-jsem coordination and fall back to -j<N> per GHC invocation. Users
must upgrade to a cabal-install that supports protocol v2 to recover
full parallelism.

Also fix a leak in cleanupSem (#27253): cleanupSem used to snapshot
heldTokens and release them before killing the loop, while the loop's
in-flight acquire/release children could still be mutating it.
Cleanup now runs inside the loop's own exit handler, after draining
the active child via a new activeChild TVar, so the snapshot has no
concurrent mutator.

See also:
- GHC proposal amendment: https://github.com/ghc-proposals/ghc-proposals/pull/673
- cabal-install patch: https://github.com/haskell/cabal/pull/11628
- semaphore-compat MR: https://gitlab.haskell.org/ghc/semaphore-compat/-/merge_requests/8

Bump semaphore-compat submodule to 2.0.0

Fixes #25087 and #27253

17be4f1f

by Alan Zimmerman at 2026-05-26T04:54:52-04:00

EPA: Record semicolons in HsModifier

Ensure the semi colons are captured in the ParsedSource for code like

  %True;; %False;
  instance C D

It makes HsModifier (and hence HsModifierOf) LocatedA, so the semi
colons can be recorded as [TrailingAnn]

Also rename pprHsModifiers to pprLHsModifiers to match.

Closes #27294

8f991755

by fendor at 2026-05-26T11:02:52-04:00

Revert prog003 acceptance

We thought the commit 286f1adff3e78d775ff325caff71d0cee25d710b fixed the
test, but due to changes to ghci, modules loaded during the GHCi
session, the test was actually no longer testing what it set out to do,
"fixing" the broken test.

As modules are added to the `interactive-session` home unit, the object code needs
to be compiled with `-this-unit-id interactive-session`, otherwise the
object code won't be used.
Once this has been fixed in the test, the test fails as expected again.

277a3687

by mangoiv at 2026-05-26T11:03:40-04:00

libraries/process: bump submodule to v1.6.29.0

This submodule bump resolves a segfault on macos 15.
Fixes #27144

6779bb0c

by mangoiv at 2026-05-26T11:03:40-04:00

libraries/unix: in submodule, don't pick branch 2.7

The 2.7 branch is outdated and the module has been advanced far beyond
it anyway, so remove that line.

4a645683

by Simon Peyton Jones at 2026-05-27T21:41:59-04:00

Trim the continuation in mkDupableContWithDmds

When there are no remaining argument demands, it means the application
is bottoming. In this case, we can trim the continuation to avoid the
panic that was observed in #27261.

See Note [Trimming the continuation for bottoming functions] in
GHC.Core.Opt.Simplify.Iteration.

8ab506ff

by Cheng Shao at 2026-05-27T21:42:47-04:00

ghci: fix module name string lifetime in hs_hpc_module invocation

This patch makes hpcAddModule pass a properly malloced module name
string to hs_hpc_module, instead of using useAsCString which causes
use-after-free of module name string. Fixes #27297.

Co-authored-by: Codex <codex@openai.com>

b0233814

by sheaf at 2026-05-27T21:43:31-04:00

Relax acceptance threshold for T10421

As seen in #27289, the 1% acceptance threshold for this text was
overly narrow, resulting in spurious test failures. This commit widens
the acceptance threshold to 2%. Fixes #27289.

63ce5770

by Luite Stegeman at 2026-05-28T12:23:35-04:00

Fixes for black holes

 - suspend duplicate work for eager black holes
 - detect eager black holes in checkBlockingQueues
 - don't overwrite existing black holes even if they're not
     in an eager blackhole frame
 - don't deadlock on self when thunk is already blackholed

Fixes #26936

037a80dc

by Tom McLaughlin at 2026-05-28T12:24:36-04:00

Event/Windows.hsc: rethrow exceptions in overlapped IO

This prevents the WinIO manager from swallowing exceptions in overlapped IO. It
was added to make WinIO support possible in the `network` library. See
https://gitlab.haskell.org/ghc/ghc/-/issues/27283.

We also bump __IO_MANAGER_WINIO__ to 2 so libraries can gate on this using CPP.

2d53bcdb

by Wolfgang Jeltsch at 2026-05-28T12:25:21-04:00

Allow `downsweep` to use nodes of an existing module graph

To this end, `downsweep` has not been able to use the nodes of a module
graph obtained from a previous downsweeping round. In some GHC API
applications, downsweeping is performed somewhat incrementally and
therefore could profit from reusing such existing results. This
contribution makes this possible.

Resolves #27054.

Co-authored-by: Matthew Pickering <matthewtpickering@gmail.com>

f4fbb583
by Simon Jakobi at 2026-05-28T12:26:04-04:00
```
Add regression test for T11226

Closes #11226.
```

ed29a5e6

by Sven Tennie at 2026-05-28T17:30:36-04:00

Add optional config setting for LibDir (#19174)

Previously, the `libDir` was derived from `topDir`. This won't work for
inplace stage2 cross-compilers where binaries and libraries are in
different stage dirs (`_build/stage1/` for executables and
`_build/stage2` for libraries).

`LibDir` is set in the inplace `settings` files. For bindists, we
generate a new `settings` file with no `LibDir` entry. GHC then defaults
to use `topDir` as `libDir` again. This keeps the bindist relocatable.

If `LibDir` is a relative path, it is interpreted relatively to
`topDir`.

The global package db is part of the `lib/` folder. If we want to point
for inplace cross-compilers to the succeeding stage's folder, this is
done by setting `LibDir`. Thus, the global package db must be found
relative to `libDir`` (which may default to `topDir` or be set by
`LibDir`).

The complexity of settings becomes scary. So, add a test to ensure
`LibDir` works as expected.

8339cf8f

by Sven Tennie at 2026-05-28T17:30:36-04:00

Add Haddock to FileSettings

Helping to understand the fields' meanings without deeper analyses.

4ce251e4

by Sylvain Henry at 2026-05-28T17:31:39-04:00

foundation test: skip signed minBound `quot` (-1) (#27222)

`minBound `quot` (-1)` for fixed-width signed integers is platform
dependent: the mathematical result -minBound is not representable in
the type. On x86, IDIV traps; LLVM's sdiv is undefined behaviour in
this case; on AArch64/RISC-V, SDIV wraps to minBound.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

b8ba7e61

by Simon Jakobi at 2026-05-28T17:32:23-04:00

Prevent dictionary-passing in checkTyEqRhs

...by pre-specializing it to TcM.

Previously, wherever checkTyEqRhs was used in other modules, the
Core showed dictionary passing ($fMonadIOEnv). The added SPECIALIZE
pragma prevents this.

d603477f

by David Eichmann at 2026-05-29T13:17:12-04:00

Hadrian: create a ghc-internal .def file per ghc-internal dll

The .def file generated from rts/win32/libHSghc-internal.def.in contains
the name of the ghc-internal dll. The correct dll name differs based
on if the dll is inplace/final and if using the Dynamic way. Previously,
this was not accounted for and inconsistent dlls names where used. That
led to failure when loading dlls at runtime in experiments with windows
dynamic linking.

1fc21753

by Sylvain Henry at 2026-05-29T13:18:14-04:00

ghc-bignum: copy backend interface haddocks to Native backend (#27305)

The haddock comments documenting the BigNat backend interface (function
contracts, expected MutableWordArray# sizes, return-value semantics, etc.)
were attached to the FFI backend module. Copy them to the Native backend
so they remain in tree once the FFI backend is removed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

717059df

by Sylvain Henry at 2026-05-29T13:18:14-04:00

ghc-bignum: remove FFI backend (#27305)

The FFI backend of ghc-bignum (now part of ghc-internal) had no known
users and is easy to recreate by relinking ghc-internal with a custom
backend. Remove the backend module, the bignum-ffi cabal flag, and the
ffi option from Hadrian's --bignum selector. The backend interface
documentation now lives in the Native backend module.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

4bb3b1d8

by Sylvain Henry at 2026-05-29T13:18:14-04:00

ghc-bignum: remove Check backend (#27305)

The Check backend of ghc-bignum (now part of ghc-internal) compared the
selected backend's output against the Native backend for validation.
It had no known users. Remove the backend module, the bignum-check
cabal flag, the bignumCheck Hadrian flavour field, and the check-
prefix in Hadrian's --bignum selector.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

6b3044a0
by David Eichmann at 2026-05-30T11:58:48-04:00
```
Add code comments to allocator code
```

f4e04210

by Matthew Pickering at 2026-05-30T11:59:34-04:00

hadrian: Refactor system-cxx-std-lib rules

I noticed a few things wrong with the hadrian rules for
`system-cxx-std-lib` rules.

* For `text` there is an ad-hoc check to depend on `system-cxx-std-lib`
outside of `configurePackage`.
* The `system-cxx-std-lib` dependency is not read from cabal files.
* Recache is not called on the packge database after the `.conf` file is
generated, a more natural place for this rule is `registerRules`.

Treating this uniformly like other packages is complicated by it not
having any source code or a cabal file. However we can do a bit better
by reporting the dependency firstly in `PackageData` and then needing
the `.conf` file in the same place as every other package in
`configurePackage`.

This commit increases the `shakeVersion`, to provide backwards
compatibility to previous builds with different PackageData.

Fixes #25303

Co-authored-by: Sven Tennie <sven.tennie@gmail.com>

576987d0

by Simon Jakobi at 2026-06-02T04:53:36-04:00

compiler: use nubOrd from containers

Address #27103 by replacing GHC.Utils.Misc.ordNub[On] with
Data.Containers.ListUtils.nubOrd[On].

Note that nubOrd suffers from a small inefficiency, a fix for which
will be included in the next containers release:

  https://github.com/haskell/containers/issues/1202

deea53c3

by David Eichmann at 2026-06-02T04:54:22-04:00

Hadrian: disable response files for GHC/Haddock builders on non-Windows

This makes debugging build errors easier on non-windows hosts.
See issue #27230

f2f5c6ba
by Nikita Efremov at 2026-06-02T16:04:54+00:00
```
fix typo : compete with performance, not complete
```

5524ea0e

by Wolfgang Jeltsch at 2026-06-03T08:01:26-04:00

Make the current `base` buildable with GHC 9.14

This comprises the following changes:

  * Disable some imports into `GHC.Base` for GHC 9.14
  * Disable some imports into `Prelude` for GHC 9.14
  * Disable separate `ArrowLoop` import for GHC 9.14
  * Disable `GHC.Internal.STM` import for GHC 9.14
  * Disable `GHC.Internal.Unicode.Version` import for GHC 9.14
  * Disable `GHC.Internal.TH.Monad` import for GHC 9.14
  * Add alternative `fixIO` import for GHC 9.14
  * Add alternative `unsafeCodeCoerce` import for GHC 9.14
  * Disable hiding of imported SIMD operations for GHC 9.14
  * Disable use of GHC 9.14’s `printToHandleFinalizerExceptionHandler`
  * Enable use of `getFileHash` from `ghc-internal` for GHC 9.14
  * Make `thenA` available for GHC 9.14
  * Make `thenM` available for GHC 9.14
  * Disable translation of `IoManagerFlagPoll` for GHC 9.14
  * Add `hGetNewlineMode` for GHC 9.14

d3438055
by Enrico Maria De Angelis at 2026-06-03T08:02:17-04:00
```
Fix #27067 - Clarify haddocks on `minusNaturalMaybe`
```

f9bcfac2

by sheaf at 2026-06-03T14:47:19-04:00

Avoid mkTick in Core Prep breaking ANF

As discovered in #27182, mkTick can break ANF. This patch introduces a
variant of mkTick that skips the single optimisation that could break
ANF. This is preferrable over switching to the raw Tick constructor,
as the latter may introduce spurious cost centres in profiling reports.

This is a temporary measure until we more thoroughly refactor how
mkTick works (see #27141).

See Note [mkTick breaks ANF] in GHC.CoreToStg.Prep.

Fixes #27182

cf1fd661

by Artem Pelenitsyn at 2026-06-03T14:48:09-04:00

clarify comment for getSizeofMutableByteArray#: we get the size in bytes, not "elements"

a3b431f3

by David Eichmann at 2026-06-04T10:10:19+00:00

Hadrian: convert env variable ACLOCAL_PATH to unix paths.

Convert ACLOCAL_PATH to a unix style path when invoking autoreconf.
Autoreconf doesn't handle windows paths.
See Note [Autoreconf unix paths from ACLOCAL_PATH].

Fixes #27311

18f6138a

by Simon Jakobi at 2026-06-04T20:20:31-04:00

testsuite: Deduplicate --only test names

config.only is assumed to be a set, but supplying --only overwrote it
with the (list) argparse result, which can contain duplicates. When a
test ran, config.only.remove(name) dropped only the first occurrence,
so a duplicated name lingered and was later misreported as a
"test not found" framework failure. Store it as a set instead.

Fixes #27322

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

2f3cc9ff

by Simon Jakobi at 2026-06-08T07:55:49-04:00

testsuite: detect fast bignum via ghc-internal, not removed ghc-bignum

The ghc-bignum package was merged into ghc-internal, so the BIGNUM_GMP
probe in test.mk ran `ghc-pkg field ghc-bignum exposed-modules`, which
fails with "cannot find package ghc-bignum". That error went to stderr
and leaked into the captured stderr of every makefile_test, causing
spurious [bad stderr] failures across the suite. The probe also silently
returned empty, so config.have_fast_bignum was wrongly False even on GMP
builds.

Probe ghc-internal's extra-libraries for the gmp library instead: the
GMP backend module is an other-module (not exposed), but GMP_LIBS adds
gmp to extra-libraries only on a GMP build, so this distinguishes the
backends. Redirect stderr to keep any future missing-package error off
the harness's stderr.

This also removes a stale comment as per suggestion from hsyl20.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

eb3bf6e7

by Alan Zimmerman at 2026-06-08T07:56:32-04:00

EPA: Rename Transform.anchorEof to addModuleCommentOrigDeltas

This now matches what it actually does.

498bb21a

by David Eichmann at 2026-06-09T18:02:39-04:00

Hadrian: avoid response files when command line is short enough

This replaces the logic of always using response files on Windows.
With the new condition based on command line lenght, reponse files
can be avoided in many more cases (on windows).

Now that response files are only used in a small number of cases,
response files are always kept and the -r / --keep-response-files
command line options have been removed

The response file paths are nolonger randomized. They are placed in the
`_build/rsp` directory. This ensures they are ignored by git and we
that Hadrian reuses response file paths when rebuilding rather than
leaving stale response files around.

Update user guide putting response files in its own section

87f510a5
by Simon Hengel at 2026-06-09T18:03:25-04:00
```
Don't use non-breaking spaces
```

41a19379

by David Eichmann at 2026-06-09T18:04:11-04:00

Hadrian: remove unused wrapper scripts from windows bindist

These wrapper scripts are only installed on non-relocatable builds
which are not generally supported on windows.

ce01ccb6

by sheaf at 2026-06-10T05:08:48-04:00

Don't drop ticks around variables of type `IO ()`

GHC.Core.Utils.mkTick is responsible for placing a tick on a Core
expression. It contains logic for dropping SCCs (non-counting profiling
ticks) around non-function variables, as such variables cannot
meaningfully contribute to profiles. However, the logic for what counts
as a function was incorrect: it used `isFunTy` which returns 'False' for
types such as 'IO ()' where the function arrow is hidden under a
newtype.

We now use 'mightBeFunTy' instead of 'isFunTy'. This ensures we don't
drop ticks in cases we aren't sure.

On the way, we improve the documentation of 'isFunTy', 'isPiTy' and
'mightBeFunTy', and update the latter's implementation to consistently
handle unary classes.

Fixes #27225

-------------------------
Metric Decrease:
    T5642
-------------------------

d311c4f1

by Simon Jakobi at 2026-06-10T05:09:32-04:00

testsuite: Add regression test for #4081

Check that a strict constructor field is unboxed once outside an
enclosing loop, not re-inspected each iteration (the float-out
case-floating from 9cb20b488). Uses simonpj's `data T a = T !a` example
from the ticket; T4081.stderr captures the expected Core.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

333df444

by sheaf at 2026-06-10T05:10:25-04:00

Check for cabal-install >= 3.12 upfront

Starting with commit 8cb99552f607f6bc4000e45ab32532d50c8bb996, Hadrian
requires cabal-install >= 3.12 in order to use the 'cabal path' command
that was introduced in version 3.12, as per
  https://github.com/haskell/cabal/blob/a51c4ee1556d816ad86e90db7e6330dd51b0b6e7/release-notes/cabal-install-3.12.1.0.md?plain=1#L45

This was not reflected in the Hadrian build script, causing a delayed
build failure instead of enforcing the version requirement upfront,
which this patch does.

Fixes #27317

98c20394

by sheaf at 2026-06-10T05:11:09-04:00

Fix crash in Data.Data instance for HsCtxt

The Data.Data instance for HsCtxt contained an error for the 'toConstr'
method, which could trigger for example when looking at -ddump-tc-ast
traces. Replace it with the 'abstractConstr' pattern used in the rest of
the codebase.

5ac9ce7d

by Zubin Duggal at 2026-06-10T21:26:32+05:30

hadrian: Remove old package.conf files when generating new ones

Old package.conf files might exists with different hashes, causing issues like #26661

Fixes #26661

c9015f09

by sheaf at 2026-06-11T12:40:28-04:00

Fix AArch64 clobbering bug for MUL2

On AArch64, the code generator could clobber one of the input operands
when computing the lower bits of a MUL2 operation. This rendered invalid
the subsequent computation of the high bits.
This commit fixes that by using a temporary register. The register
allocator can remove the redundant move in the common case when the
registers do not conflict.

Fixes #27046

7ab90288

by Rodrigo Mesquita at 2026-06-11T12:41:11-04:00

fix: make T27131 less flaky

It seems that T27131 fails flakily in a race where we check the flag
before the capability had the chance to process the mailbox which sets
the flag. This seemingly should only happen if the capability ends up
being the same for setting and checking the flag.

8965cb76
by Marc Scholten at 2026-06-12T04:53:22-04:00
```
haddock: render modules concurrently
```

8cc0b64a

by Duncan Coutts at 2026-06-12T04:54:06-04:00

Promote HAVE_PREEMPTION from Timer.c to OSThreads.h

We will want to know about HAVE_PREEMPTION in more places.

HAVE_PREEMPTION tells us that we do have OS threads available,
irrespective of whether THREADED is defined. In particular,
HAVE_PREEMPTION is defined on all proper OSs, but not on WASM (and
hyopthetically may not be true on some other platforms like
micro-controllers, RTOSs, VM hypervisors etc).

cce574ed

by Duncan Coutts at 2026-06-12T04:54:06-04:00

Define ACQUIRE_LOCK_ALWAYS and friends

Fix issue #27335

Like the atomic _ALWAYS variants, these lock actions are always defined,
rather than being dependent on whether we are in the THREADED case. All
the "normal" LOCK macros are defined to be no-ops when !THREADED.

The use case for the _ALWAYS variants is where we are using OS threads
even in the non-threaded RTS. This includes everything to do with the
timer/ticker thread, which is used in the non-threaded RTS too.

In particular, we will want to use this for eventlog things, because the
timer thread performs eventlogging concurrently with the main
capability, even in the non-threaded RTS.

1f28d1f6

by Duncan Coutts at 2026-06-12T04:54:06-04:00

Use ACQUIRE/RELEASE_LOCK_ALWAYS with eventBufMutex

Even in the non-threaded RTS the eventBufMutex is needed by both the
main capability and the timer/ticker thread, so always use the mutex.

This should fix #25165 which is about the main capability and the timer
thread posting events to the eventlog buffer concurrently and thereby
corrupting the buffer data.

0ff29782

by Duncan Coutts at 2026-06-12T04:54:06-04:00

Expose eventBufMutex in the EventLog interface/header

We will need it in forkProcess to ensure we don't write to the global
eventlog buffer concurrently with trying to flush eventlog buffers and
do the fork().

7a688395

by Duncan Coutts at 2026-06-12T04:54:07-04:00

Split flushAllCapsEventsBufs into safe and unlocked version

Following the convention that unlocked versions have a trailing _
underscore in their name. This one requires the caller to hold the
eventlog global buffer mutex. We will need this in forkProcess.

341ed474

by Duncan Coutts at 2026-06-12T04:54:07-04:00

Remove redundant use of stopTimer in setNumCapabilities

Historically, the comment here was:

  We must stop the interval timer while we are changing the
  capabilities array lest handle_tick may try to context switch
  an old capability. See #17289.

and

  We must disable the timer while we do this since the tick handler may
  call contextSwitchAllCapabilities, which may see the capabilities array
  as we free it.

What this refers to is that historically, when changing the number of
capabilities, the array of capabilities was reallocated to a new size,
allocating new ones and freeing the old ones, thus invalidating all
existing capbility pointers.

Strangely, for good measure the code used to call stopTimer twice (hence
the two similar comments above).

However, since commit a3eccf06292dd666b24606251a52da2b466a9612, the
capabilities array is no longer reallocated. Instead the array is
allcoated once on RTS startup to the maximum size it could ever be
allowed to be, and then capabilities get enabled/disabled at runtime. So
the capability pointers never become invalid anymore. At worst, they may
point to capabilities that are disabled.

Thus we no longer need to stop the timer (twice) while we change the
number of enabled capabilities. This also partially solves issue #27105,
which notes that stopTimer is being used as if it were synchronous, when
it is not. At least for this case, the solution is that stopTimer is not
needed at all!

674858e3

by Duncan Coutts at 2026-06-12T04:54:07-04:00

Remove redundant use of stopTimer in forkProcess

but replace it with taking the eventlog buffer lock during the fork.

Fixes issue #27105

The original reason to block the timer during a fork was that
historically the timer was implemented using a periodic timer signal,
and the signal itself would interrupt the fork system call (returning
EINTR). For large processes (where fork() takes a while) this could
permanently livelock: the timer always would go off before the fork
could complete, which got retried in a loop forever.

The timer is no longer implemented as a unix signal, but uses threads.
Thus the original problem no longer exists. The only remaining reason to
block the timer tick is to prevent actions taken by the tick from
interfering with the delicate process involved in fork (taking a load of
locks and pausing everything).

The only thing we need to do is to prevent the eventlog from being
written to or flushed while the fork is taking place. To achieve this
all we need to do is hold the mutex for the global eventlog buffer.

This removes the last use of stopTimer that expects stopTimer to work
synchronously (which it was not) and thus solves issue #27105. To be
clear, we solve issue #27105 not by making stopTimer synchronous, but by
eliminating the use sites that expected it to be synchronous.

eb64f6fa

by Duncan Coutts at 2026-06-12T13:37:09+01:00

Add a test for thread scheduler fairness

It also tests that the interval timer and context switching works.
We also test that fairness is lost when the context switching interval
is too coarse for the duration of the test.

We add this test before doing surgery on the interval timer, so we have
decent coverage.

b98680f0

by Duncan Coutts at 2026-06-12T13:37:09+01:00

Make exported stop/startTimer no-ops, and rename internal functions

Specifically, internally rename:
stop/startTimer to pause/unpauseTimer
stop/startTicker to pause/unpauseTicker

and keep stop/startTimer as exported functions, but now as no-ops.

In the past the stop/startTicker actions were used incorrectly as if
they were synchronous, which they are not. See issue #27105. We now
document pause/unpackTicker as being async and not to be used for the
purpose of concurrency safety.

The existing stop/startTimer (note Timer not Ticker, the Timer calls the
Ticker!) are also exported from the RTS as a public API. This was
historically because the ticker used signals and it was important to
suspend the timer signel over a process fork. So these functions were
exported to be used by the process and unix libraries.

We cannot just remove the RTS exports, but we now make them no-ops, and
they can be removed from the process and unix library later. This
was already documented in a changelog.d entry no-more-timer-signal but
due to changes during the MR process the change to make stop/startTicker
into no-ops didn't make it into the earlier MR.

c09e823b

by Duncan Coutts at 2026-06-12T13:37:09+01:00

Make exitTicker/exitTimer unconditionally synchronous

We never use them asynchronously, and we should never need to do so.

And update some related comments.

1d60852d

by Duncan Coutts at 2026-06-12T13:37:09+01:00

posix ticker: update and improve comments on (un)pause and exit

Clarify what is async vs sync.

7bcd9b93