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Alan Zimmerman pushed to branch wip/az/exactprint-annotation-rationalisation at Glasgow Haskell Compiler / GHC

Commits:

ac870ad5

by Simon Jakobi at 2026-10-28T04:40:42-04:00

X86 NCG: use 32-bit POPCNT for sub-word popcounts

A 32-bit write zero-extends the result to the full register, so we
don't need to emit additional code for this.

We also skip emitting zero-extension instructions for the argument
when it is already visibly zero-extended.

For the byte-wise popcount loop from #24813, this shrinks the popcount
sequence from 5 instructions to 3.

Assisted-by: Claude Fable 5.1

53087373

by Facundo Domínguez at 2026-10-28T04:41:32-04:00

Use a ShortByteString in Serialized instead of [Word8]

This makes the in-memory representation 40x more compact for all values
stored in annotations.

A test is added to measure the representation size of annotations
specified in the compiler input.

The GHC API is modified. All functions that previously handled annotations
in [Word8] form now use ShortByteString. The following definitions have
modified types:

  * GHC.findGlobalAnns
  * GHC.Tc.Gen.Splice.getAnnotationsByTypeRep
  * GHC.Core.Opt.Monad.getAnnotations
  * GHC.Core.Opt.Monad.getFirstAnnotations
  * GHC.Types.Annotations.deserializeAnns
  * GHC.Types.Annotations.findAnns
  * GHC.Types.Annotations.findAnnsByTypeRep
  * GHC.Serialized.Serialized
  * GHC.Serialized.toSerialized
  * GHC.Serialized.fromSerialized
  * GHC.Serialized.serializeWithData
  * GHC.Serialized.deserializeWithData
  * GHCi.Message.ReifyAnnotations

Fixes #28002.

cc533b66

by Sasha Bogicevic at 2026-10-31T09:18:15-04:00

Don't report -XStrict-generated bangs under -Wredundant-bang-patterns

The -XStrict flag causes the desugarer to insert bang patterns.
These are not user-written, so -Wredundant-bang-patterns must not
report them.

To achieve this, the desugarer now tracks whether it is desugaring
compiler-generated code (similar to the typechecker's 'tcl_in_gen_code').
Bangs inserted by -XStrict are given generated spans, which suppresses
the "redundant bang" warnings without otherwise affecting pattern-match
warnings.

Fixes #27323

13d38047

by Luite Stegeman at 2026-10-31T09:19:11-04:00

rts: tombstone Weak# copies that lose an evacuation race (#23160)

Mark the losing copy of a Weak# during an evacuation race in parallel
GC with stg_DEAD_WEAK_info. This ensures that the nonmoving GC
doesn't follow dangling pointers, leading to crashes.

Fixes #23160

63347328

by Zubin Duggal at 2026-10-31T09:19:52-04:00

ghci: Drop GHCi's exception context when rethrowing in ghc -e

Fixes #27847.

a85fef3f

by Zubin Duggal at 2026-10-31T09:19:52-04:00

base: Preserve exception context in modifyIOError

Fixes #27851.
CLC proposal: https://github.com/haskell/core-libraries-committee/issues/446

1d60b591

by Zubin Duggal at 2026-10-31T09:19:52-04:00

base: Preserve exception context in mapException

Fixes #27851.
CLC proposal: https://github.com/haskell/core-libraries-committee/issues/446

3c029a1b

by Zubin Duggal at 2026-10-31T09:19:52-04:00

base: Preserve exception context when rethrowing exceptions in Handle reads

Fixes #27875.
CLC proposal: https://github.com/haskell/core-libraries-committee/issues/447

ab2b317a

by Zubin Duggal at 2026-10-31T09:19:52-04:00

base: Preserve exception context when rethrowing exceptions in hClose

Fixes #27875.
CLC proposal: https://github.com/haskell/core-libraries-committee/issues/447

f5abf277

by Zubin Duggal at 2026-10-31T09:19:52-04:00

base: Preserve exception context when rethrowing exceptions in Windows openFile

Fixes #27875.
CLC proposal: https://github.com/haskell/core-libraries-committee/issues/447

d842c672

by Zubin Duggal at 2026-10-31T09:19:52-04:00

base: Preserve exception context when rethrowing exceptions in executablePath

Fixes #27875.
CLC proposal: https://github.com/haskell/core-libraries-committee/issues/447

c5a8bb9f

by Simon Peyton Jones at 2026-10-31T09:20:34-04:00

Simplify a tc-trace which could crash the compiler

The trace formatted an error message, which prematurely
read the ExpType in a FunResCtxt.

Solution: don't put call the error message formatting
when tc-tracing.

ab49b1d2
by Simon Peyton Jones at 2026-10-31T09:20:34-04:00
```
Tiny comment change to uniqAway
```

6efe4ba3

by Simon Peyton Jones at 2026-10-31T09:20:34-04:00

Make niFixSubst idempotent

I discovered (when fixing #27994) that `niFixSubst` didn't actually
generate an idempotent subsitution despite its claims.  It could
return a substitution that mentions domain variables on in its range,
when those variables are hidden inside the kind of a type variable
occurrence.  As a result it can generate ill-kinded types. Boo!

The fix is simple, and uses deep substitution.
See Note [Finding the substitution fixpoint]

I don't think it actually /caused/ any bugs, so there is no
regression test.

3b60ae7e

by Simon Peyton Jones at 2026-10-31T09:20:34-04:00

Fix a nasty bug in fundeps

This MR fixes #27994, which turned out to be very tricky.

See Note [Exploiting closed type famililes], especially (CF7).  I was
ending up with TyVars (not TcTyVars) in the solver, because the
substitution computed in `getRelevantBranches` mixed the two.

The code was just too clever. I ended up simplifying it quite a bit.
For /closed/ families we no longer call `trimQtvs` (was `trim_qtvs`).

Open families still do use `trimQtvs`.  See Note [trimQTvs]

This patch also fixes one other buglet in the same code.

* Over-saturated type families were being mis-handled.
  See the new use of `saturatedFamApp_maybe`.

e4610f2d

by Facundo Domínguez at 2026-10-31T09:21:24-04:00

Have haddock --incremental look for the module in -this-unit-id

bc6c0db6

by sheaf at 2026-10-31T09:22:20-04:00

mightBeFunTy: hotfix for #27979

ce01ccb6 refactored 'GHC.Types.RepType.mightBeFunTy' to look through
unary classes. That change introduced the helper function 'unwrap_type'
which was supposed to always return an unwrapped type, but its fallback
equation mistakenly returned the original type. This caused the
subsequent 'tyConAppTyCon_maybe' to fail in cases where it should
succeed (e.g. looking through foralls).

In this commit, we move all the unary class unwrapping logic into
'unwrapType' where it belonged from the start, and update the
documentation of 'unwrapType' to better explain what it should be used
for (#26695).

Fixes #27979 #26695

-------------------------
Metric Increase:
    T5642
-------------------------

233cce46

by Alan Zimmerman at 2026-10-31T09:23:01-04:00

EPA: Tidy up ExactPrint.markAnnListA' 

It takes an action which can modify the AnnList, but this
is never used. So remove it.

3594a908

by Sylvain Henry at 2026-10-31T09:23:51-04:00

gitmodules: ignore dirty libffi-clib submodule (#26785)

`./boot` runs autoreconf in libraries/libffi-clib, which leaves
`configure~` behind and rewrites the tracked `aclocal.m4` whenever the
local automake version differs from the one that generated it. Every
checkout then looks dirty. Ignore working-tree changes in the submodule
(`ignore = dirty`); a changed submodule commit is still reported.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

341223c0

by Rodrigo Mesquita at 2026-10-31T09:24:33-04:00

refactor: Keep the interactive Ids directly rather than Name

Removes things like

    names <- map idName ids
    map (\i -> let id = find (\x -> i==idName x) names) idso

and is more straightforward because there's less state going around (no
more updating HscEnv as an output)

It also kills `printTypeOfNames` completely, since now we just have the
Ids. No longer `lookupName` names to get back the ids...

```
printTypeOfName :: GHC.GhcMonad m => Name -> m ()
printTypeOfName n
   = do maybe_tything <- GHC.lookupName n
        case maybe_tything of
            Nothing    -> return ()
            Just thing -> printTyThing thing
```

now is just `printTyThing . AnId`

Also:
```diff
-  tythings <- catMaybes `liftM` mapM GHC.lookupName namesSorted
-  docs <- mapM pprTypeAndContents [i | AnId i <- tythings]
+  docs <- mapM pprTypeAndContents idsSorted
```

(and yes, in ExecBreaks there are only Ids, no TyThings, bc they are
only constructed by the interpreter execution which can only bind ids.
for TyThings use runDecls which doesn't return execBreaks.)

There's some care to be had to make sure we use the "most refined" Ids,
whereas when using `Name`s we'd always fetch the most refined Id from
scratch.

Fixes #28052

54cf3c1e

by sheaf at 2026-11-03T07:00:23-05:00

Consolidate all CPU feature handling

This commit introduces GHC.Platform.CpuFeatures which consolidates all
of the logic for implications between CPU feature flags (mainly X86):

  - DynFlags now only records the set of -m<feature> flags that were
    passed, as an EnumSet CpuFeature. That keeps it a simple record of
    the flags the user passed, with no post-processing.

  - GHC.Platform.CpuFeatures.initCpuFeatures turns this set into a
    CpuFeatures value, applying all implications and the per-architecture
    baseline. This is the single home for all of the feature implication
    logic.

    Some datatypes were reworked to better reflect the implication
    structure in the types, e.g. SseAvxVersion has a strategically
    placed 'FMA' boolean.

  - The NCG, LLVM backend, StgToCmm, CPP defines and LLVM -mattr
    flags all consult CpuFeatures, via targetCpuFeatures.

See Note [CPU features], which replaces
Note [Implications between X86 CPU feature flags].

Behaviour changes:

  - x86 feature flags (-msse3, -mavx, -mavx512*, -mgfni, ...) passed
    when targeting a non-x86 architecture no longer cause x86 CPP
    macros (__SSE3__, __AVX512BW__, __GFNI__, ...) to be defined, nor
    x86 attributes to be passed to LLVM.
  - Error messages reported when required CPU features are not enabled
    now print out the minimal set of flags required
    (e.g. "-mavx512vl" rather than "-mavx512f -mavx512vl").

9af64305

by Luite Stegeman at 2026-11-03T07:01:23-05:00

rts: move stack check to the start of the stg_unpack_cstring thunks

fixes a deadlock

see #27272

a2208b21

by Simon Jakobi at 2026-11-03T07:02:05-05:00

Cmm: exclude the entry block from common block elimination

a1d8139054c had fixed #27722 only partially, because it didn't prevent
elimination of the entry block in later rounds, where the entry block is
no longer guaranteed to come first.

To close this loophole, we exclude the entry block from the CBE merge
logic. See Note [Retain entry block during common block elimination] for
details.

This also deletes a misleading comment regarding unreachable blocks: the
control-flow optimiser doesn't actually guarantee that no unreachable
blocks reach CBE.

Fixes #27722.

Assisted-by: Claude Fable 5.1

37ad4710

by Alan Zimmerman at 2026-11-03T07:02:46-05:00

EPA: Use AnnList for GADT declarations

Continuing the process of using AnnList to capture parser layout

d3104741

by Alan Zimmerman at 2026-11-03T22:08:44+00:00

EPA: Use AnnList in AnnClassDecl

Capture parser layout

a9db823e

by Alan Zimmerman at 2026-11-04T18:15:40+00:00

P:EPA: Make local binds located

Use LHsLocalBinds instead of HsLocalBinds

This reverses an earlier change, and brings processing of local binds
into alignement with the exact printing principle that the LocatedA
contents provide the location and extent of the enclosed item,
together with any comments or context-specific trailing items like
commas or semi colons.

The internal TTG extension points only carry exact print annotations
related to printing the item within its bounds.

This change brings back the problem of EmptyLocalBinds, which by
definition cannot have a location. These get a noSrcSpan location,
which is ignored in the exact printing process.

2eae9880

by Alan Zimmerman at 2026-11-04T18:15:40+00:00

P:EPA: Use AnnList in HsMultiIf

It introduces layout, capture it

24145a53
by Alan Zimmerman at 2026-11-04T18:15:40+00:00
```
P:EPA: Use AnnList in DecBrl
```

5bf2bcba

by Alan Zimmerman at 2026-11-04T18:15:40+00:00

P:EPA: Replace AnnListLayout / AnnListBrackets with EpLayout

534d431f

by Alan Zimmerman at 2026-11-04T18:15:40+00:00

P:WIP: setLayoutBoth inside markAnnListA

Current problem is it is a global one-shot, and MG has one too

Check: is it needed?
       if so, honouring EpLayout may be needed

fef95d30
by Alan Zimmerman at 2026-11-04T18:15:40+00:00
```
P:EPA some tests for layout. WIP
```

e87a925e

by Alan Zimmerman at 2026-11-04T18:20:24+00:00

MOVE EPA: Plan for Fixing AnnList Layout Properly 

Also Exactprint layout scope plan

a8a83f6b
by Alan Zimmerman at 2026-11-04T18:20:49+00:00
```
P:EPA: tidy up a bit. Combine somewhere else
```

d77e6ef6