GitLab

Zubin pushed to branch ghc-10.0 at Glasgow Haskell Compiler / GHC

Commits:

4da783a3

by Rodrigo Mesquita at 2026-06-09T15:02:45+05:30

Add test for #25636

The existing test behaviour of "T23146_liftedeq" changed because the
simplifier now does a bit more inlining. We can restore the previous bad
behavior by using an OPAQUE pragma.

This test doubles as a test for #25636 when run in ghci, so we add it as
such.

(cherry picked from commit d1ddfd4bcb71d771eab69ca26b855fe1bb4e56ce)

dacdffe0

by Rodrigo Mesquita at 2026-06-09T15:02:50+05:30

refactor: protoBCOName is always a Name

Simplifies the code by removing the unnecessary type argument to
ProtoBCO which was always 'Name'

(cherry picked from commit b9df40eed42f487c470758c52ce26b532466f8af)

1434980c

by Rodrigo Mesquita at 2026-06-09T15:02:59+05:30

Allocate static constructors for bytecode

This commit adds support for static constructors when compiling and
linking ByteCode objects.

Top-level StgRhsCon get lowered to ProtoStaticCons rather than to
ProtoBCOs. A ProtoStaticCon gets allocated directly as a data con
application on the heap (using the new primop newConApp#).

Previously, we would allocate a ProtoBCO which, when evaluated, would
PACK and return the constructor.
A few more details are given in Note [Static constructors in Bytecode].

Secondly, this commit also fixes issue #25636 which was caused by
linking *unlifted* constructors in BCO instructions as
    - (1) a thunk indexing the array of BCOs in a module
    - (2) which evaluated to a BCO which still had to be evaluated to
      return the unlifted constructor proper.

The (2) issue has been resolved by allocating the static constructors
directly. The (1) issue can be resolved by ensuring that we allocate all
unlifted top-level constructors eagerly, and leave the knot-tying for
the lifted BCOs and top-level constructors only.

The top-level unlifted constructors are never mutually recursive, so we
can allocate them all in one go as long as we do it in topological
order. Lifted fields of unlifted constructors can still be filled by the
knot-tied lifted variables since in those fields it is fine to keep
those thunks. See Note [Tying the knot in createBCOs] for more details.

Fixes #25636

-------------------------
Metric Decrease:
    LinkableUsage01
-------------------------

(cherry picked from commit 5c2a179efea36296c35f2c273eb614e3efd89f78)

359df3a6

by Rodrigo Mesquita at 2026-06-09T15:03:39+05:30

Revert "StgToByteCode: Assert that PUSH_G'd values are lifted"

This reverts commit ec26c54d818e0cd328276196930313f66b780905.

Ever since f7a22c0f4e9ae0dc767115d4c53fddbd8372b777, we now do support
and will link top-level unlifted constructors into evaluated and
properly tagged values which we can reference with PUSH_G.

This assertion is no longer true and triggered a failure in T25636

(cherry picked from commit cde4705344642cc8a188bcad5a71d99a9ca59e8c)

54ffdbcf

by Rodrigo Mesquita at 2026-06-09T15:03:46+05:30

refactor: Tag more remote Ptrs as RemotePtr

Pure refactor which improves the API of

- GHC.ByteCode.Linker
- GHC.Runtime.Interpreter
- GHC.Runtime.Interpreter.Types.SymbolCache

by using `RemotePtr` for more functions which used to return `Ptr`s that
could potentially be in a foreign process. E.g. `lookupIE`,
`lookupStaticPtr`, etc...

(cherry picked from commit c7a7e5b8d6e75223bfd48da447d8a7bb7c99688b)

3583edee

by Rodrigo Mesquita at 2026-06-09T15:03:54+05:30

Add float# and subword tests for #25636

These tests cover that static constructors in bytecode work correctly
for Float# and subword values (Word8#, Word16#)

(cherry picked from commit fc59494c363f692bd073d12c7a08331ff02b9bb0)

3b9e67ef

by Rodrigo Mesquita at 2026-06-09T15:04:01+05:30

test: Validate topoSort logic in createBCOs

This test validates that the topological sorting and ordering of the
unlifted constructors and lifted constructors in `createBCOs` is
correct.

See `Note [Tying the knot in createBCOs]` for why tying the knot for the
created BCOs is slightly difficult and why the topological sorting is
necessary.

This test fails when `let topoSortedObjs = topSortObjs objs` is
substituted by `let topoSortedObjs = zip [0..] objs`, thus witnessing
the toposort logic is correct and necessary.

The test calls the ghci `createBCOs` directly because it is currently
impossible to construct in Source Haskell a situation where a top-level
static unlifted constructor depends on another (we don't have top-level
unlifted constructors except for nullary constructors like `Leaf ::
(UTree :: UnliftedType)`).

This is another test for fix for #25636

(cherry picked from commit 477f521bec17f475e611da3efd28cba106f86017)

fc901f8d

by sheaf at 2026-06-09T15:14:39+05:30

Simplify mkTick

This commit simplifies 'GHC.Core.Utils.mkTick', removing the
accumulating parameter 'rest' which was suspiciously treating a bunch of
different ticks as a group, and moving the group as a whole around the
AST, ignoring that the ticks in the group might have different placement
properties.

The most important change is that we revert the logic (added in 85b0aae2)
that allowed ticks to be placed around coercions, which caused serious
issues (e.g. #27121). It was just a mistake, as it doesn't make sense
to put a tick around a coercion.

Also adds Note [Pushing SCCs inwards] which clarifies the logic for
pushing SCCs into lambdas, constructor applications, and dropping SCCs
around non-function variables (in particular the treatment of splittable
ticks).

A few other changes are also implemented:

  - simplify 'can_split' predicate (no functional change)
  - combine profiling ticks into one when possible

Fixes #26878, #26941 and #27121

Co-authored-by: simonpj <simon.peytonjones@gmail.com>
(cherry picked from commit 2dadf3b0d057c087af812e5dd33fe4135a4ef19f)

ed6ed37b

by sheaf at 2026-06-09T15:14:39+05:30

Deal with 'noSpec' in 'coreExprToPmLit'

This commit makes two separate changes relating to
'GHC.HsToCore.Pmc.Solver.Types.coreExprAsPmLit':

  1. Commit 7124e4ad mistakenly marked deferred errors as non-canonical,
     which led to the introduction of 'nospec' wrappers in the
     generated Core. This reverts that accident by declaring deferred
     errors as being canonical, avoiding spurious 'nospec' wrapping.
  2. Look through magic identity-like Ids such as 'nospec', 'inline' and
     'lazy' in 'coreExprAsPmLit', just like Core Prep does.
     There might genuinely be incoherent evidence, but that shouldn't
     obstruct the pattern match checker. See test T27124a.

Fixes #25926 #27124

-------------------------
Metric Decrease:
    T3294
-------------------------

(cherry picked from commit e8a196c65cee32f06c3d99b74af33457511408c7)

a6d10535

by Luite Stegeman at 2026-06-09T15:14:39+05:30

rts: add a few missing i386 relocations in the rts linker

(cherry picked from commit 04d143c02e82e9ca03eb75849959d369d07fb81a)

71e68812

by Luite Stegeman at 2026-06-09T15:14:39+05:30

CodeOutput: Fix finalizers on multiple platforms

 - ELF platforms: emit .fini_array section
 - wasm32/Darwin: emit initializer with __cxa_atexit call
 - Windows: use -Wl,--whole-archive to prevent dropping finalizer symbols
 - rts linker: fix crash/assertion failure unloading objects with finalizers

fixes #27072

(cherry picked from commit 014087e7a5753687161a24a1b2bc55c7bf7273fd)

9a3ac65f

by sheaf at 2026-06-09T15:14:39+05:30

Ensure TcM plugins are only initialised once

This commit ensures we keep TcM plugins (typechecker plugins,
defaulting plugins and hole fit plugins) running all the way through
desugaring, instead of stopping them at the end of typechecking.

To do this, the "stop" actions of TcPlugin and DefaultingPlugin are
split into two: one for the "post-typecheck" action, and one for the
final shutdown action (after desugaring).

This allows the plugins to be invoked by the pattern match checker
(during desugaring) without having to be repeatedly re-initialised and
stopped, fixing #26839.

In the process, this commit modifies 'initTc' and 'initTcInteractive',
adding an extra argument that describes whether to start/stop the 'TcM'
plugins.

See Note [Stop TcM plugins after desugaring] for an overview.

(cherry picked from commit 1350271b55e30e8b4c3e7b61af889906d82f5e93)

8c48198c

by Simon Peyton Jones at 2026-06-09T15:14:39+05:30

Fix assertion check in checkResultTy

As #27210 shows, the assertion was a little bit too eager.

I refactored a bit by moving some code from GHC.Tc.Gen.App
to GHC.Tc.Utils.Unify; see the new function tcSubTypeApp,
which replaces tcSubTypeDS

(cherry picked from commit 9797052b974b3356c34b457558ffda3c1b6a0c48)

75cd9831

by Rodrigo Mesquita at 2026-06-09T15:14:39+05:30

New rts Message to {set,unset} TSO flags

This commit introduces stg_MSG_SET_TSO_FLAG_info and
stg_MSG_UNSET_TSO_FLAG_info, which allows setting flags of a TSO other
than yourself.

This is especially useful/necessary to set breakpoints and toggle
breakpoints of different threads, which is needed to safely implement
features like pausing, toggling step-out, toggling step-in per thread,
etc.

Fixes #27131

-------------------------
Metric Decrease:
    T3294
-------------------------

(cherry picked from commit 5bd6a96485ff9bfcbf06eaec69776bf8af61b563)

43f4503a

by Rodrigo Mesquita at 2026-06-09T15:14:39+05:30

test: Add test setting another TSO's flags

Introduces a test that runs on two capabilities. The main thread running
on Capability 0 sets the flags on a TSO running on Capability 1.
The TSO from Capability 1 itself checks whether its flags were set and
reports that back.

This validates that the RTS messages for setting TSO flags work, even if
it doesn't test a harsher scenario with race conditions to exercise why
the message passing is necessary for safely setting another TSO's flags.

Part of #27131

(cherry picked from commit ce97fd3ed13028034ba27c34a6decdb3460aa4eb)

b44312d2

by Wen Kokke at 2026-06-09T15:14:39+05:30

rts: Add dynamic trace flags API

This commit adds an API to the RTS (exposed via Rts.h) that allows users to dynamically change the trace flags.
Prior to this commit, users were able to stop and start the profiling and heap profiling timers (via startProfTimer/stopProfTimer and startHeapProfTimer/stopHeapProfTimer).
This extends that functionality to also cover the core event types.

The getTraceFlag/setTraceFlag functions read and write the values of the trace flag cache, which is allocated by Trace.c, rather than modifying the members of RtsFlags.TraceFlags.
This is done under the assumption that the members of RtsFlags should not be modified after RTS initialisation.
Consequently, if the user modifies the trace flags using setTraceFlag, the object returned by getTraceFlags (from base) will not reflect these changes.

The trace flags are not protected by locks of any sort.
Hence, these functions are not thread-safe.
However, the trace flags are not modified by the RTS after initialisation, only read, so the race conditions introduced by one user modifying them are most likely benign.

This PR also puts the trace flag cache in a single global struct, as opposed to a collection of global variables, and changes the types of the individual flags from uint8_t to bool, as these have the same size on both Clang and GCC and are a better semantic match.
Prior to the change to uint8_t, they had type int, see 42c47cd6.
Even with its deprecation in C23, I don't think there should be any issue depending on stdbool.h.
The TRACE_X macros are redefined to access the global struct, with values cast to const bool to ensure they are read-only.

(cherry picked from commit 1cb1d6728f6c0e83669f2956f3c061966886e4b6)

e668a66c

by Wen Kokke at 2026-06-09T15:14:39+05:30

rts: Ensure TRACE_X values are used in place of RtsFlags.TraceFlags.X

(cherry picked from commit 9d54dc947704eb446f8821ae03c421960639cdbd)

531f361f

by Wen Kokke at 2026-06-09T15:14:39+05:30

rts: Fix nonmoving-GC tracing

The current nonmoving-GC tracing functions were written in a different
style from the other tracing functions. They were directly implemented
as, e.g., a traceConcMarkEnd function that called postConcMarkEnd.
The other tracing functions are implemented as, e.g., traceThreadLabel_,
a function that posts the thread label event, and traceThreadLabel, a
macro that checks whether TRACE_scheduler is set. This commit fixes that
implementation, and ensures that the nonmoving-GC tracing functions only
emit events if nonmoving-GC tracing is enabled.

(cherry picked from commit 418d737b7494d978cf77d567014ae28dadf1359c)

61b588bc

by Wen Kokke at 2026-06-09T15:14:39+05:30

rts: Add SymI_HasProto for get/setTraceFlag

(cherry picked from commit 99f4afa41dc1a8817cf5fe9dda76e3f1bae09f69)

a0255ae3

by Wen Kokke at 2026-06-09T15:14:39+05:30

rts: Add SymI_HasProto for start/endEventLogging

(cherry picked from commit 7e9eb8b9d47d9e2115612155ea8800cfbd20bc5f)

f07b0b95

by Wen Kokke at 2026-06-09T15:14:39+05:30

rts: Add changelog entry

(cherry picked from commit 3a3045fb1a21c1f8f90e4ab88f93ea3f4d238a49)

1cba5109

by Wolfgang Jeltsch at 2026-06-09T15:14:40+05:30

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>
(cherry picked from commit 5fab22387a66657e5e19f1ba490f09af1168eb06)

854f2f07

by Cheng Shao at 2026-06-09T15:14:40+05:30

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.

(cherry picked from commit 38b76b2f1d918f10d2f9d3e57bd0459dfe671d4f)

354bc995

by Ian Duncan at 2026-06-09T15:14:40+05:30

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.

(cherry picked from commit 50188615342098345fc2822ea223ab23791bbf49)

5514629c

by Wen Kokke at 2026-06-09T15:14:40+05:30

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.

(cherry picked from commit 41c2448bbaed232cdd647f7d152e7872e57e3a9a)

ac9aedf9

by Wen Kokke at 2026-06-09T15:14:40+05:30

ghc-internal: Add TraceFlags.traceIPE

(cherry picked from commit 62536551ae2fd77640f9507f72ad9cd229b40833)

491ac71e

by Wen Kokke at 2026-06-09T15:14:40+05:30

testsuite: Add test for TraceFlags.traceIpe

(cherry picked from commit e45312d10dc8005be96af78732d78d9cfc0ad912)

324c2a59

by Wen Kokke at 2026-06-09T15:14:40+05:30

ghc-internal: Add DebugFlags.ipe

(cherry picked from commit 4768d9aa13beb60bf3c4d8a8d1c609f3ca7dfdd3)

dc637bd6

by Wen Kokke at 2026-06-09T15:14:40+05:30

testsuite: Add test for DebugFlags.ipe

(cherry picked from commit bc1b5c69d9500d032d6124450f19a687a8b684a5)

ee40a14e

by fendor at 2026-06-09T15:14:40+05:30

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.

(cherry picked from commit 286f1adff3e78d775ff325caff71d0cee25d710b)

0477d638

by fendor at 2026-06-09T15:14:40+05:30

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.

(cherry picked from commit 728662de2084069ef53bd5adf2c0e8b1e8814bc0)

983f69a7

by fendor at 2026-06-09T15:14:40+05:30

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.

(cherry picked from commit 50e999cae0297be156d3cc6a683fc3c7634428f0)

f31c6475

by sheaf at 2026-06-09T15:15:53+05:30

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.

(cherry picked from commit 7ecc618466382588b9934c514f178e0b6ff41f49)

cd744705

by Alan Zimmerman at 2026-06-09T15:15:53+05:30

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

(cherry picked from commit 3268c610d7011d3b0d2a9357f59ab7aeb47e2da1)

e2ec33fc

by Alan Zimmerman at 2026-06-09T15:18:24+05:30

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

(cherry picked from commit 1f09679081816acb86fd02eb332f0dff7133ddf1)

73350b8d

by Cheng Shao at 2026-06-09T15:22:30+05:30

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.

(cherry picked from commit cccf45da01988801b0c97f7e7ed0160191980226)

bd2307ab

by Zubin Duggal at 2026-06-09T15:22:30+05:30

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

(cherry picked from commit 8db331a381ae47ad9ad5c8613f5d3e2588d5dd55)

de5db87e

by Alan Zimmerman at 2026-06-09T15:22:30+05:30

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

(cherry picked from commit 17be4f1f6be288a03c87778797964cdc51adc8ff)

d9ee32e8

by fendor at 2026-06-09T15:22:30+05:30

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.

(cherry picked from commit 8f9917557a7ef290dfa8b913c3a4146289586ec6)

e271d8ca

by mangoiv at 2026-06-09T15:22:30+05:30

libraries/process: bump submodule to v1.6.29.0

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

(cherry picked from commit 277a3687c4b729e4d1ff4d4503a5673deba5eda7)

a7539ec5

by mangoiv at 2026-06-09T15:23:54+05:30

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.

(cherry picked from commit 6779bb0c2d2784182465337ba5e94b7cd8810f2b)

48c5e0ae

by sheaf at 2026-06-09T15:24:06+05:30

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.

(cherry picked from commit b0233814d63c2802a521dfc7dae08b1ecf494c50)

7e645dbd

by Luite Stegeman at 2026-06-09T15:24:06+05:30

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

(cherry picked from commit 63ce5770da1712f0da54665d8755772bf38ba51e)

1bd35b2e

by Tom McLaughlin at 2026-06-09T15:24:06+05:30

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.

(cherry picked from commit 037a80dc65d3975adf4a35d46876850e644bc80e)

42193da3

by sheaf at 2026-06-09T15:24:06+05:30

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

(cherry picked from commit f9bcfac2e92457128f5c82dea181edcd0baf7eef)

207b6cc6

by mangoiv at 2026-06-09T15:37:22+05:30

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.

This patch was rewritten to avoid pulling in a refactor.
The original patch is included in master as 4a645683

(cherry picked from commit 53f74985860b35a879bfd0dc642e7fcafffcf5e4)

69561925

by sheaf at 2026-07-20T14:25:36+05:30

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
-------------------------

(cherry picked from commit ce01ccb625514a09e76aded549691da4dfe87de7)

d035085a

by sheaf at 2026-07-20T14:25:43+05:30

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.

(cherry picked from commit 98c20394e8a130df928272c360199fb5e9265f22)

4a70cf55

by sheaf at 2026-07-20T14:25:43+05:30

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

(cherry picked from commit c9015f0953e72829e89ac768b6ad9ece34c7e187)

f17ccdf3

by sheaf at 2026-07-20T14:25:43+05:30

Add type family performance test for #26426

Some GHC versions produced large numbers of coercions after typechecking
and desugaring when compiling the program in #26426:

Version | Typechecker time | Typechecker allocations | Coercions
-------:|-----------------:|------------------------:|---------:
9.6     |   47 ms          |  48 MB                  |    110k
9.8     | 1000 ms          | 486 MB                  | 10,437k
9.10    |  922 ms          | 489 MB                  | 10,436k
9.12    |  906 ms          | 482 MB                  | 10,437k
9.14    |   63 ms          |  55 MB                  |    333k
10.0    |   47 ms          |  64 MB                  |     35k

The improvement 9.12 -> 9.14 was due to commit 22d11fa818fae2c95c494fc0fac1f8cb4c6e7cb6,
while the improvement 9.14 -> 10.0 was due to commit 0b7df6db9e46df40e86fbff1a66dc10440b99db5.

As the behaviour of GHC seems better than it's ever been on this program,
we declare victory, adding this performance test to ensure we don't
regress on this program.

On the way, we update Note [Combining equalities] in GHC.Tc.SolveR.Equality
with the explanation of the 9.12 -> 9.14 improvement (getting rid of an
exponential blowup in coercion sizes), and we update
Note [Exploiting closed type families] in GHC.Tc.Solver.FunDeps with
the explanation of the 9.14 -> 10.0 improvement (bringing down coercion
size growth from cubic to quadratic).

(cherry picked from commit 40764930f10d73f6ca00dfbbce908f9516d262ce)

eca8e6eb

by mangoiv at 2026-07-20T14:25:48+05:30

libraries/process: bump submodule to v1.6.30.0

- bump the submodule to the appropriate tag
- suppress benign warning resulting from the change

(cherry picked from commit d9ea2d76545452a7df567b162340079cb024a40c)

7aba67c2

by ARATA Mizuki at 2026-07-20T14:25:57+05:30

RISC-V NCG: Zero-extend the result of castFloatToWord32

According to the ISA manual, FMV.X.W sign-extends the result.
We need to truncate the result to avoid creating an exotic Word32 value.

Fixes #27300

(cherry picked from commit 291ce3aafe4ca3d2562154a28c595a858987d9f1)

9dba4f96

by ARATA Mizuki at 2026-07-20T14:25:57+05:30

RISC-V NCG: Treat d28-d31 (ft8-ft11) as caller-saved

According to the calling convention, the registers d28-d31 (ft8-ft11) are caller-saved.

Fixes #27306

(cherry picked from commit 011be91fdaa7869dff2f30b8f2ecca3c9a713739)

4e7a3d23

by ARATA Mizuki at 2026-07-20T14:25:57+05:30

RISC-V NCG: Set rounding mode when emitting `truncate`

If we omit the rounding mode for `fcvt`, `dyn` will be used.
We do not want that for `truncate`, so we set `rtz`.
In other places, we set `rne` because we do not use the dynamic rounding mode.

Fixes #27303

(cherry picked from commit e8a547133031b7de8f6f9bbd70a7148eda0941ee)

b9d78ac1

by Zubin Duggal at 2026-07-20T14:25:57+05:30

rts: fix validate build with gcc 16. `__attribute__((regparm(1)))` is ignored on x86_64 and now
gcc warns that it is ignored:

rts/sm/Evac.h:35:1: error:
     error: ‘regparm’ attribute ignored [-Werror=attributes]

See https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=ccead81bbc39668376eb5cf47066acb446cc43f3

Fixes #27366

(cherry picked from commit 9438bec7117433bbc70449d4288f6ee32dbbbec4)

dfd1dd1b

by Ian Duncan at 2026-07-20T14:25:58+05:30

AArch64: use SXTH, not SXTW, for W32 signExtendReg

signExtendReg was using SXTH (sign-extend halfword, 16-bit) for
W32-to-W64 sign extension. This should be SXTW (sign-extend word,
32-bit). SXTH only sign-extends the lower 16 bits, producing wrong
results for 32-bit values whose bit 15 differs from bit 31.

Other fixes:

  - At sub-W64, code gen for MO_S_Mul2 should use W32 registers for
    SMULL source operands as per the ARM spec (SMULL Xd, Wn, Wm),
    and not W64.

  - Ensure signExtendReg uses the source width for the source operand
    in SXTW/SXTH/SXTB instructions. GNU as requires sxtw Xd,Wn (not
    sxtw Xd,Xn), while LLVM's integrated assembler on macOS is lenient.

  - Fix overflow flag computation for `MO_S_Mul2`. The overflow bit
    was exactly inverted for sub-W64 operands.

Fixes #26978 and #27047

(cherry picked from commit 636c1c7ae47495f022affa501ea0a40cb55cd4a4)

36de60c2

by Luite Stegeman at 2026-07-20T14:25:58+05:30

tag inference: don't confuse functions with their return values

inferTagRhs was mixing up taggedness for closures and return values
for function closures. We really shouldn't assign TagTuple to a
properly tagged function returning a tuple.

We fix this by keeping track of functions (TagFun) separately from
values (TagVal) and keeping track of their return value. TagFun is
also used for join points.

fixes #27005

(cherry picked from commit 7fe4f2ec3ce12ea138177c81a019dcfc148fe5d4)

caac944f

by Sebastian Graf at 2026-07-20T14:26:25+05:30

Desugar a `case` scrutinee only once (#27383, #20251)

In `dsExpr` for `HsCase` we desugared the scrutinee /twice/: once to
build the Core `case` itself, and again inside `matchWrapper`, which
re-desugared the source scrutinee (via `addHsScrutTmCs`) purely to
record long-distance information for the pattern-match checker.

For a single `case` that is merely wasteful.  But for nested cases it
is catastrophic.  Consider

    case (case (case e of ... ) of ... ) of ...

Desugaring the outer scrutinee desugars the middle `case` twice, each
of which desugars the inner `case` twice, and so on.  The work doubles
at every level, so desugaring takes O(2^n) time in the nesting depth.
That is the blowup reported in #27383; it is also what makes the
machine-generated program in #20251 take an age to compile.

The fix is simple.  `matchWrapper` is handed the scrutinee anyway, so
we give it the Core expression we have /already/ desugared, and record
the long-distance term constraint with `addCoreScrutTmCs` instead of
re-desugaring from source.  This is just what `matchSinglePatVar`
already does for single-pattern matches.

So:

* `matchWrapper` now takes `Maybe [CoreExpr]` rather than
  `Maybe [LHsExpr GhcTc]`.

* The `HsCase` equation of `dsExpr` passes the already-desugared
  `core_discrim`; the arrow desugarer passes its match variables.

* `addHsScrutTmCs` had no other use, so it is gone.

Desugaring is now linear in the nesting depth.  (The coverage checker
still runs `simpleOptExpr` over each scrutinee, which leaves the total
at O(n^2); that is ample.)  The long-distance information itself is
unchanged: the checker sees precisely the Core that backs the
generated code.

Test: deSugar/should_compile/T27383
(cherry picked from commit 67d41299be96798702377e6e2b826f9c8e070821)

26c22c6e

by sheaf at 2026-07-20T14:26:26+05:30

Avoid mkTick in Core Prep breaking ANF (part II)

Hotfix for 2f9579765f55b3920ceb2e04995ff41a9d0e2d4e fixing a small
oversight in the call to tickTickedExpr from mkTick, in which we
improperly recursively called mkTick without passing on the preserve_anf
flag.

Fixes #27386

(cherry picked from commit 473b97ebc742305f56e30d5b1bbf95b7681312f0)

4872ef31

by Simon Hengel at 2026-07-20T15:39:29+05:30

Reference correct package in error messages for reexported modules

(fixes #27417)

(cherry picked from commit a805b2a25021606b30d250e084d4beecbfac0d0a)

9f158de1

by mangoiv at 2026-07-20T15:39:29+05:30

compiler: rename ZonkAny to UnusedType and add pretty printing logic

ZonkAny is a hard to understand name for users who do not know how the
compiler works internally. Additionally, it is confusing that ZonkAny,
while being a concrete type *represents* a meta variable, espeically in
the compiler output.
This patch changes the name of ZonkAny to UnusedType which is closer to
its intended semantics and adds special pretty printing logic to display
this type in the same fashion the compiler displays meta variables in
other places, whenever they leak from the implementation to the user.
It also exports the type from ghc-internal:GHC.Internal.Types in order
to expose documentation.

Fixes #27390

Co-Authored-By: Sam Derbyshire <sam.derbyshire@gmail.com>
(cherry picked from commit a72ff58fa86172b1557e405f7246d27914fdae6e)

7f19139e

by Luite Stegeman at 2026-07-20T15:39:29+05:30

rts: handle large AP closures in compacting GC

The function update_fwd_large in the compacting GC could run into
an unexpected object with the following error:

  internal error: update_fwd_large: unknown/strange object  24

Closure type 24 is the AP closure, which was not handled in
upd_fwd_large. This patch adds handling them.

fixes #27434

(cherry picked from commit cca0d58963f802a8b2e43aa2dbc58592f8ad07bb)

34a825d4

by Cheng Shao at 2026-07-20T15:39:29+05:30

compiler: fix missing handling of CmmUnsafeForeignCall node in LayoutStack

This patch fixes missing handling of `CmmUnsafeForeignCall` middle
node in the `LayoutStack` pass.

Before proc-points splitting, this pass computes liveliness of local
registers, and spills those alive across a Cmm native call onto the
stack. It need to traverse all middle nodes in each block and check
whether a local register is an assignee, if so then the previous
mapping in `sm_regs` is invalidated and needs to be dropped. However,
it didn't handle `CmmUnsafeForeignCall` node which may also assign to
a local register. When proc-points splitting is enabled, this can
produce an invalid basic block that doesn't properly backup the
updated local register to the stack before doing a Cmm call, resulting
in completely invalid runtime behavior.

The patch also adds a `T27447` regression test. With no-TNTC or with
LLVM backend, without the fix the test case would output a stale
0x1111111111111111 value, instead of the expected 0x2222222222222222
output.

Fixes #27447.

Co-authored-by: Codex <codex@openai.com>
(cherry picked from commit 3f00f234d0d5b3b3b2a23a5dc70ce372eb9bbdb4)

835ed6f2

by mangoiv at 2026-07-20T15:39:29+05:30

ci: retry fetching test metrics

Retry fetching test metrics to make the CI not fail if the services is
temporarily unavailable

(cherry picked from commit b7e24044fde064cb3f0d44c36872a86d024cd7d4)

89a634fc

by Zubin Duggal at 2026-07-20T15:39:29+05:30

Bump semaphore-compat submodule to 2.0.1

This versions includes some cruicial fixes for darwin

(cherry picked from commit 4180af3f71754472dbd49b85179b25fd29bd9998)

e5b1fab6

by Zubin Duggal at 2026-07-20T15:39:29+05:30

CorePrep: Don't speculatively evaluate bindings that we have already discovered to be absent

In #25924, we segfault because speculation forces a projection out of a RUBBISH dictionary
(which we generated because it absent).

Solution: Don't speculate on bindings we already know are absent.

Fixes 25924

(cherry picked from commit 9b714c4c833461c621f0a050680848d7248aa57e)

ebe99a26

by Zubin Duggal at 2026-07-20T15:39:29+05:30

Don't make absent fillers for terminating types

In #25924 we discovered that we could speculatively evaluate an absent filler
for a dictionary, and project a field (a superclass selector) out of it,
resulting in segfaults.

Solution: Never make an absent filler or rubbish literal for a terminating type
like a dictionary. mkAbsentFiller returns Nothing for isTerminatingType, so
worker/wrapper and the specialiser keep the real argument instead.

Some small metric decreases because we do a little less work in the
simplifier now.

Metric Decrease:
    T9872a
    T9872b
    T9872c
    TcPlugin_RewritePerf

(cherry picked from commit 4a59b3eece9b7106fcbe73d2d06a49755be4ea8f)

2d4a6f31

by Andreas Klebinger at 2026-07-20T15:39:29+05:30

Fix a profiling race condition resulting in segfaults.

StgToCmm: Don't assume tagged FUN closures in closureCodeBody.
When entering a closure the self/node pointer might not be tagged in
some situations when a thunk is evaluated by multiple threads.
So we most AND away the tag bits rather than subtracting an expected tag.

Apply.cmm: Fix a race condition occuring when a thunk is mutated during GC.

In stg_ap_0_fast when might need to run GC before entering a thunk. If this happens
another thread or the GC itself might mutate the closure making entering it no longer
valid. We now check for this.

Add test and changelog for #27123 fixes.

(cherry picked from commit ed09895d7de1ca116a561868c151fd825a16ad0c)

5775b5ca

by Cheng Shao at 2026-07-20T15:39:29+05:30

ghc-heap: fix invalid srtlen returned by peekItbl when no-TNTC

This patch fixes the no-TNTC code path of `peekItbl` so that it looks
at the right memory address when reading the `srt` field from the
`StgInfoTable_` struct. Also adds a `T27465` regression test that
reproduces the bug on no-TNTC builds before the fix. Fixes #27465.

Co-authored-by: Codex <codex@openai.com>
(cherry picked from commit 67c03eb2c762fdfeb646eb8345341173dd4268b2)

cb19b6c5

by Andrea Vezzosi at 2026-07-20T15:39:29+05:30

[Fix #27287] preserve ModBreaks in ModIface

(cherry picked from commit 4396a6f2a4c7799908e1e0b88a218a51d063fdca)

e401ef1c

by Zubin Duggal at 2026-07-20T15:39:29+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

(cherry picked from commit 5ac9ce7d3821c75e2d2cc17fae00b9e865a02987)

7f50e6d6

by Cheng Shao at 2026-07-20T15:39:29+05:30

compiler: fix miscompiled %load_relaxed, add missing %store_relaxed

This patch fixes the %load_relaxed cmm primop compilation logic to
correctly use relaxed memory ordering, and adds the missing
%store_relaxed primop. Parsing logic of %load/%store with explicit
ordering is covered in the AtomicFetch test case. Fixes #27483.

Co-authored-by: Codex <codex@openai.com>
(cherry picked from commit eee8ec5b25ef0f83ba4822e7a0a941df7b0bec5f)

d184ea5d

by Cheng Shao at 2026-07-20T15:39:29+05:30

rts: fix missing UNTAG in stg_readTVarIOzh

This patch fixes missing UNTAG on the current value closure read from
StgTVar. UNTAG is a no-op when it's stg_TREC_HEADER_info which is word
aligned; it may be a tagged closure, and reading info table from the
tagged address is an unaligned load which may cause issues on
platforms with strict alignment requirements.

Co-authored-by: Codex <codex@openai.com>
(cherry picked from commit d377e83e51d39a06e1f0bf2e35a923a3210b21a2)

2036f996

by Cheng Shao at 2026-07-20T15:39:29+05:30

rts: fix missing UNTAG in stg_control0zh_ll

This patch fixes missing UNTAG on the cont closure returned by
captureContinuationAndAbort. In case it's not NULL,
captureContinuationAndAbort returns a tagged StgContinuation closure,
in which case it must be untagged before accessing the
apply_mask_frame field.

In the past it worked out of luck: when apply_mask_frame was NULL then
mask_frame_offset is also 0 so the control flow didn't diverge to a
wrong path. Still, this is horribly wrong and will crash once
StgContinuation struct is refactored and fields are shuffled around.

Co-authored-by: Codex <codex@openai.com>
(cherry picked from commit 8ed038421a20e3e4e681973b2f5098e5bd2144b5)

3b82fd7f

by Cheng Shao at 2026-07-20T15:39:29+05:30

compiler: fix redundant AP thunk codegen when not using -ticky-ap-thunk

This patch fixes a double negation confusion in !7525 that results in
some redundant AP thunk code generation when not using
-ticky-ap-thunk. Now, we use `stgToCmmUseStdApThunk` to indicate
whether precomputed AP thunks in the RTS should be used, which
defaults to `True`, unless `-ticky-ap-thunk` is passed.
`-finfo-table-map` now also implies `-ticky-ap-thunk`, since when
doing IPE profiling we want the generated AP thunks to be unique.
Fixes #27502.

-------------------------
Metric Decrease:
    T3064
-------------------------

Co-authored-by: Codex <codex@openai.com>
(cherry picked from commit 5aa7000ae246ae6a706437799338295b5801a629)

c25a2d92

by Brian McKenna at 2026-07-20T15:39:29+05:30

Strip ticks when desugaring bool guards

The special `considerAccessible` pattern was broken when compiling
with debug info. Compiling with debug info wraps expressions with
`SourceNote` ticks, which broke the internals of the
`desugarBoolGuard` function. Ticks are now ignored within this
function.

Fixes #27360

(cherry picked from commit d43a7b7ad90047f1445c88d796ee7b15a0a605d7)

42778740

by Ben Gamari at 2026-07-20T15:39:29+05:30

base: Display ExceptionContext in WhileHandling's textual description

As originally-implemented the implementation for
`WhileHandling(displayExceptionAnnotation)` would display the
`ExceptionContext` of the exception which it carries (as this was the
behavior of `displayException`, in terms of which
`displayExceptionAnnotation` was implemented).

However, in 284ffab3 the definition of `SomeException(displayException)`
was changed to exclude the `ExceptionContext`. This means that
`WhileHandling(displayExceptionAnnotation)` fails to describe the
provenance of the exception which it captures, greatly limiting its
utility.

Return the implementation to its originally-specified behavior by
implementing `WhileHandling(displayExceptionAnnotation)` in terms of
`displayExceptionWithInfo`.

Fixes #27456.

(cherry picked from commit ede4b17bdc54c055e44ad95711409c7d1dcb1128)

cd1fdc26

by Brian McKenna at 2026-07-20T15:39:29+05:30

Ignore ticks in the pattern-match term oracle

The term-oracle in the pattern-match checker is keyed by a canonical
form of the scrutinee, computed by `makeDictsCoherent`. That canonical
form was tick-sensitive: two occurrences of an otherwise identical
expression that happened to carry different ticks were treated as
distinct values, breaking long-distance information.

This shows up in practice under `-finfo-table-map`, because the
desugarer wraps every record-selector use site in a `SourceNote`
carrying that site's span. For example:

     data Box = Box { unBox :: Maybe Int }
     f b = case unBox b of
       Nothing -> 0
       Just _  -> let Just x = unBox b in x

The two `unBox b` expressionss carry different SourceNote spans, the
pattern-match checker sees them as different, the long-distance
information from the outer `Just _` branch never reaches the
let-pattern, and `Just x = unBox b` is wrongly reported as
non-exhaustive.

We now strip all ticks in `makeDictsCoherent`.  This is documented as
Wrinkle (UD1) of Note [Unique dictionaries in the TmOracle CoreMap].

Fixes #27314

(cherry picked from commit b388d0934c0933c1cdb47226489634e229239d0a)

2a27443f

by Duncan Coutts at 2026-07-20T15:39:29+05:30

Fix failing test GcStaticPointers for non-moving GC

Minor mistake in asserting something before checking for that same
thing.

Specifically, Bdescr asserts HEAP_ALLOCED_GC, but Bdescr was being used
prior to a guard that checks HEAP_ALLOCED_GC. The solution is just to
move the use of Bdescr after the guard.

Thanks to Simon Jakobi for identifying the problem.

(cherry picked from commit 42918646169c7c5ba61912b39b5f5147bf1d255c)

b11f2da2
by Zubin Duggal at 2026-09-03T13:18:46+05:30
```
Bump Cabal submodule to 3.18.1.0
```

ad7709f1

by Cheng Shao at 2026-09-03T13:18:46+05:30

rts: always use StgInt to represent cost center id

Currently cost center id is modeled as `Int` and it should be `StgInt`
uniformly in the RTS, hence this patch. Fixes #27524.

(cherry picked from commit ab9ab8952b1ff20ed8b092ff95d6a9f8d822c033)

788db729

by Zubin Duggal at 2026-09-17T09:02:48+05:30

UniqueDFM: alter should preserve insertion order

Before it always inserting new elements at the end.
This is problematic because instances get inserted into the map with
`alterF`, which can change ordering of how instances are printed
with `:info` depending on the order in which we consult interfaces

I expect `alter id k = id` and `alter (fmap f) k = adjust f k`. Moving keys to
the end breaks that (`adjust` already preserves position).

Fixes #27532

(cherry picked from commit f6f2343fbbfdfd8aaed9babf5983e3e24c08ca85)

4fa83928

by Duncan Coutts at 2026-09-17T09:02:48+05:30

Add missing updateRemembSetPushClosure in poll I/O manager

For the non-moving GC.

(cherry picked from commit daf2bd6f71b7ee309374dddf0d4793bbc0ed066d)

473ef734