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Magnus pushed to branch wip/mangoiv/27556 at Glasgow Haskell Compiler / GHC

Commits:

c77d88fc

by sheaf at 2026-08-13T10:15:22-04:00

Allow rewriting in RuntimeReps for newtype ConPats

This commit implements PHASE 2 of the FixedRuntimeRep plan described in
Note [The Concrete mechanism] in GHC.Tc.Utils.Concrete for newtype
constructor patterns.

In short, GHC now accepts programs of the form

  f (MkN x) = ...

in which the argument 'x' of the newtype constructor pattern 'MkN x'
has a representation that is not syntactically concrete, e.g. it can be
'Id IntRep' reducing to 'IntRep'. See T20363{,b,c} for examples.

There are two main parts to the implementation:

  1. Typechecking, in GHC.Tc.Gen.Pat.tcDataConPat.
     See Note [Typechecking newtype constructor patterns] in GHC.Tc.Gen.Pat.

  2. Desugaring. We restructure the code for desugaring pattern matches
     by allowing the scrutinised match variable to be casted. This allows
     us to accumulate coercions and avoids creating binders at intermediate
     types tha don't have a fixed RuntimeRep.
     See the revamped Note [Match Ids] in GHC.HsToCore.Monad.

Fixes #20363

-------------------------
Metric Increase:
    InstanceMatching
-------------------------

6ba9dd41

by Wolfgang Jeltsch at 2026-08-13T10:16:07-04:00

Improve the documentation of `--show-iface`

This change in particular gets rid of the claim that `--show-iface`
writes *the* contents of the interface file in question. It doesn’t do
that; it only writes those parts that are likely of interest to a human
reader.

4bd193fa

by Sylvain Henry at 2026-08-13T10:17:00-04:00

RTS: fix LDV profiler's slop skipping (#27585)

processHeapForDead was the one heap scanner not updated for the slop
marker encoding introduced in #19048. It still assumed slop is zeroed:

    while (p < bd->free && !*p) p++;   // skip slop

so it stopped at the (StgWord)(-1) sentinel and passed it to
processHeapClosureForDead. IS_FORWARDING_PTR(-1) holds, hence a garbage
size was read out of LDVW and the scan ran off the block, tripping
ASSERT(p == bd->free) on a debug RTS and silently corrupting the census
otherwise.

The loop was hand-copied in four places, so factor it out into skipSlop
in ClosureMacros.h and use it in ProfHeap.c, Sanity.c, Printer.c and
LdvProfile.c.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

1446bb03

by Zubin Duggal at 2026-08-13T10:17:48-04:00

hadrian: Fix links to remaining doc sites to not use the package hash for haddock links

In 07267f79d91169f474cacc8bcd38d76a6e97887d we changed hadrian to not include the package hash in the haddock
directory. This patch takes care of a  few remaining links that were missed in that patch

Fixes #27671

257c3ed7

by Simon Jakobi at 2026-08-13T10:18:29-04:00

Testsuite: widen InstanceMatching acceptance window to 5% (#27673)

...in order to unblock CI.

Assisted-by: Claude Fable 5

e4cfaaa0

by Simon Peyton Jones at 2026-08-14T01:09:32+02:00

Major patch to re-engineer known-key names

This big patch implements the New Plan for known-key names,
described in #27013.

Read the big Note [Overview of known-key names] in GHC.Types.Name

Some things had to be reworked slightly to accomodate the new known-keys
design. A significant one was the generation of auxiliary KindRep
bindings, which was greatly simplified. Note [Grand plan for Typeable]
was updated accordingly. Another example: GHC.Internal.CString was
merged into GHC.Internal.Types.

Co-authored-by: Rodrigo Mesquita <rodrigo.m.mesquita@gmail.com>

The couple hundreds of hours spent here by Rodrigo were sponsored by Well-Typed

Metrics: compile_time/bytes allocated
-------------------------------------
                                                       Baseline
                                  Test    Metric          value      New value Change
------------------------------------------------------------------------------------------
      MultiComponentModules100(normal) ghc/alloc 24,312,779,672 24,990,470,432  +2.8%  BAD
   MultiComponentModulesRecomp(normal) ghc/alloc    601,924,960    621,884,888  +3.3%  BAD
MultiComponentModulesRecomp100(normal) ghc/alloc 11,884,065,432 12,531,373,704  +5.4%  BAD
             MultiLayerModules(normal) ghc/alloc  3,861,537,072  3,706,919,512  -4.0% GOOD
                        T13701(normal) ghc/alloc  3,517,246,392  3,237,179,616  -8.0% GOOD
                        T13820(normal) ghc/alloc     28,961,056     29,663,208  +2.4%  BAD
                        T14697(normal) ghc/alloc    472,044,184    443,550,048  -6.0% GOOD
                        T18140(normal) ghc/alloc     47,905,664     49,115,808  +2.5%  BAD
                         T4801(normal) ghc/alloc    269,339,096    263,432,040  -2.2% GOOD
                          T783(normal) ghc/alloc    341,112,672    333,339,952  -2.3% GOOD
                hard_hole_fits(normal) ghc/alloc    222,164,728    213,433,808  -3.9% GOOD
                      mhu-perf(normal) ghc/alloc     49,011,440     46,706,280  -4.7% GOOD

                             geo. mean                                          +0.1%
                             minimum                                            -8.0%
                             maximum                                            +5.4%

All performance regressions were investigated in depth. The surviving
ones:

- MultiComponentModules100, MultiComponentModulesRecomp100,
  MultiComponentModulesRecomp regresses because existing bugs that make
  an additional implicit edge do too much redundant work: #27053 and #27461
- T13820, T18140, T10547, T13035 regress because we load an additional
  interface and associated Names for GHC.Essentials.

-------------------------
Metric Decrease:
    MultiLayerModules
    T13379
    T13701
    T14697
    T26989
    T4801
    T783
    T9961
    hard_hole_fits
    mhu-perf
    size_hello_artifact
    size_hello_obj
    size_hello_unicode
Metric Increase:
    LinkableUsage01
    LinkableUsage02
    MultiComponentModules100
    MultiComponentModulesRecomp
    MultiComponentModulesRecomp100
    T10547
    T13035
    T13820
    T18140
    T18698a
    T18698b
    T20049
-------------------------

Bumps submodule binary

Closes #27013

61665e79

by sheaf at 2026-08-14T01:09:33+02:00

Allow GHC.Essentials to be hidden

This commit overhauls several aspects of the known entity handling,
in order to allow GHC.Essentials to be hidden without a proliferation
of special cases in the compiler.

The main contribution is to introduce the 'UnresolvedImport' datatype
which cleans up a lot of ad-hoc handling relating to 'ModSummary',
fixing #27603. This allows us to reduce duplication, e.g. by having
Backpack reuse 'mkUnresolvedImports' instead of replicating the
"add implicit imports" logic. It also makes it easier to avoid
undesirable edge cases (such as making sure that the Template Haskell
'reifyModule' function does not leak the implicit GHC.Essentials import).
In particular, the infamous 'findImportedModuleWithIsBoot' is now simply
'resolveImport', taking a single 'UnresolvedImport' and resolving it
to a 'FindResult' (usually a 'Module').

Other changes:

  - Cache the result of looking up GHC.Essentials (in TcM and DsM
    environments) to avoid redundant work.
    This reduces allocations on LinkableUsage01 and hard_hole_fits.
  - Properly look up known entities for StaticPointers like we do for
    other known entities everywhere else. This allows e.g. modules in
    ghc-internal to use -XStaticPointers.
  - When using multiple home units, we are now careful to handle the
    situation in which we may have multiple GHC.Essentials modules
    around. See the new tests under 'driver/multipleHomeUnits'.

b19fcc1c

by Vladislav Zavialov at 2026-08-14T06:26:11-04:00

Increase test coverage of diagnostics, batch 2

Add test cases for the previously untested diagnostics:
  [GHC-26133] TcRnForeignImportPrimSafeAnn
  [GHC-68444] SumAltArityExceeded
  [GHC-63966] IllegalSumAlt
  [GHC-23882] IllegalDeclaration
  [GHC-60220] InvalidCCallImpent
  [GHC-18816] RecGadtNoCons
  [GHC-38140] GadtNoCons
  [GHC-37056] InvalidTypeInstanceHeader
  [GHC-78486] InvalidTyFamInstLHS
  [GHC-39639] DefaultDataInstDecl
  [GHC-78822] AssocDefaultNotAssoc
  [GHC-43510] NotSimpleUnliftedType
  [GHC-41843] IOResultExpected
  [GHC-07641] AtLeastOneArgExpected
  [GHC-52886] InvalidTopDecl

Remove unused error constructors:
  [GHC-92057] ImportLookupAmbiguous

7b27f25a

by Simon Jakobi at 2026-08-14T06:26:54-04:00

testsuite: Drop peak_megabytes_allocated from LinkableUsage tests

LinkableUsage01/02 collected all metrics with a 2% tolerance. For
peak_megabytes_allocated, whose granularity is 1 MB, that window is
under 0.7 MB at this test's ~34 MB peak, so any 1 MB step failed the
test (#27613, #27489). Drop that metric: max_bytes_used guards the
Linkable-retention property with byte granularity, at a tolerance
that still comfortably exceeds the noise observed in CI.

Assisted-by: Claude Fable 5

e5de423b

by Simon Jakobi at 2026-08-14T06:26:54-04:00

testsuite: Don't truncate fractional baselines when computing bounds

RelativeMetricAcceptanceWindow.get_bounds truncated the baseline with
int() before applying the tolerance. Baselines can be fractional (they
are averaged over several measurements), so this skewed the acceptance
window downwards: in #27613, a baseline of 33.67 at 2% tolerance
yielded bounds (32, 34) instead of (32, 35), rejecting a measurement
that was within tolerance.

Assisted-by: Claude Fable 5

db959f83

by Simon Jakobi at 2026-08-14T15:16:44-04:00

testsuite: Expect length001 failure in nonmoving_thr_sanity

length001 relies on an optimization rule to avoid excessive stack use.
The nonmoving_thr_sanity way does not enable optimization, so classify
its stack overflow as an expected failure, as is already done for the
other unoptimized nonmoving ways.

Assisted-by: gpt-5.6-sol via Codex CLI

4f2b7d90

by Simon Jakobi at 2026-08-14T15:16:44-04:00

testsuite: Omit T22859 in nonmoving threaded ways

T22859 checks allocation-limit handlers with output that depends on
precise allocation behaviour. The nonmoving threaded ways change where
these limits are reached, just as the already-omitted LLVM ways do.

Omit these ways instead of treating their incidental output differences
as test failures.

Assisted-by: gpt-5.6-sol via Codex CLI

c4abddcb

by Simon Jakobi at 2026-08-14T15:16:44-04:00

rts/js: Implement eq_thread, and test Eq/Ord ThreadId (#16761)

Since d1f3c63701, Eq ThreadId is implemented via the RTS function
eq_thread, but the JS RTS never provided it, so comparing ThreadIds
for equality on the JS backend crashed with

    ReferenceError: h$eq_thread is not defined

Like the C implementation, h$eq_thread uses pointer equality: The JS
RTS has exactly one thread object per thread.

Since previously no test exercised eq_thread directly, this commit
adds a test covering equality, its stability across GC, and agreement
with Ord.

Assisted-by: Claude Fable 5

4a7defa1

by Simon Jakobi at 2026-08-14T15:16:44-04:00

testsuite: Make listThreads1 insensitive to the RTS's own threads

listThreads1 expected `listThreads` to return exactly [ThreadId 1]. That
holds only under a non-threaded RTS. Under a threaded RTS however there
are more threads present, so we change the test to simply check that
`myThreadId` is present in the list.

Assisted-by: Claude Opus 5

b757727a

by Vladislav Zavialov at 2026-08-14T15:17:27-04:00

Fix tcLookupId panic with RequiredTypeArguments and PatternSynonyms (#27586)

The arguments declared on the left-hand side of a pattern synonym are looked up
as term variables bound by its right-hand side. Prior to this patch, that lookup
panicked with RequiredTypeArguments:

    data T a where
      MkT :: forall a -> T a

    pattern P :: Int -> T Int
    pattern P x = MkT x

On the RHS, `x` looks like a term argument, so the renamer binds it in the term
namespace. Only during type checking does it turn out to be a type variable, so
the lookup on the LHS finds an ATyVar rather than an ATcId. As the lookup was
done with tcLookupId, it resulted in a panic.

Now the arguments are looked up with tcLookupPatSynArg, which reports an illegal
term-level use of `x`, just as an ordinary function definition `f (MkT x) = x`
does.

Test cases: T27586a T27586b T27586c

Assisted-by: Claude Opus 5

c130188d