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Rodrigo Mesquita pushed to branch wip/romes/multi-threaded-debugger at Glasgow Haskell Compiler / GHC

Commits:

d2bc32aa

by Simon Peyton Jones at 2026-08-21T12:59:26-04:00

Better handling of serialisation of wired-in names

Fixes #27501

d2795ffc

by Alan Zimmerman at 2026-08-21T13:00:05-04:00

EPA: Remove NoEpTok/NoEpUniTok, using an unhelpful SrcSpan instead

Also introduce helper functions noEpTok and noEpUniTok to serve
as simple replacements in code inserting an token annotation without
location information.

b5d29ab8

by Brandon Chinn at 2026-08-25T18:42:08-04:00

Add Data.RealFloat and Infinity/NegInfinity/NaN pattern synonyms (#26961)

e60eb3bc

by Andreas Klebinger at 2026-08-25T18:42:59-04:00

rts linker: Fix pointer arithmetic issue in flushInstructionCacheRISCV64

We accidentally operated over `uint64_t*` when we should use `uint8_t`.

Fixes #27569

e9bbe8f9

by Andreas Klebinger at 2026-08-26T15:09:23-04:00

cmm dumps: Add machop width info with -dppr-debug for infix ops.

86e3a9d8

by Andreas Klebinger at 2026-08-26T15:09:24-04:00

CmmLint: Check for unsupported MachOp widths

machOpArgReps now maps MachOp + Width to a list of supported
argument widths or Nothing if the given operation is not supported
at the given width.

This allows us to check for nonsensical combinations like FloatToInt
at Word16.

Similarly we now check that every address is actually wordwidth.

13781cca

by Andreas Klebinger at 2026-08-26T15:09:24-04:00

arm64 ncg: The big subword truncation fix.

A set of slightly related fixes to arm subword handling:

Bitmask immediates:

Don't produce overflowing assembly literals.
There is still another bug here that causes us to miss some valid
literals but we will fix that later.

Improve subword truncation handling:

We now use a small set of helpers to truncate `Register` values rather
than truncating immediate `Reg` values which greatly simplifies the code
structure. This fixes a great many bugs to do with sign/zero extending subwords
or the lack thereof.

We now establish the invariant that subword values are zero-extended at
every site at which they come into "scope" of the ncg, and rely on the
invariant throughout rather than pessimistically inserting redundant
extensions in a hodgepodge manner at the use sites of these values.

This fixes at least the bugs described in issues #27533, #27430
 #27537, #27538, #27539, and #27550. But likely more bugs yet not
found.

Subword ffi results:
Apply truncations when calling functions returning
subword values.

genCondJump:
Don't sign extend signed values in the input register as
it might map to a local variable, corrupting the value stored within.

Fix subword store/load instructions.:

We used to read those at 32bit width even for smaller values possibly
resulting in invalid memory access. Now we construct the suffix for
subword variants based on the instruction format for these.

d8fa5d7c

by Andreas Klebinger at 2026-08-26T15:09:24-04:00

arm64 ncg: Fix MO_V_Broadcast for non-literals.

We now use OpReg instead of OpScalarAsVec as required since we broadcast a gp register.

Also adds a test. Fixes #27565.

94822c95

by Andreas Klebinger at 2026-08-26T15:09:24-04:00

Add some test cases covering bugs in the arm ncg.

* Test for #27430 (subword ffi results)
* #27537 - subword conversions
* #27538 - subwords used in conditional
* #27533 - single byte read

dd1ba88a
by Andreas Klebinger at 2026-08-26T15:09:24-04:00
```
cmmLint: Lint against MO_FS_Truncate subword use.
```

fd22f71e

by Zubin Duggal at 2026-08-26T15:10:20-04:00

ghc-internal: annotateSTM should use catchSTM# rather than catch#

A catch# frame inside a transaction breaks retry and async exception
delivery.

Fixes #27657

bb324171

by Rodrigo Mesquita at 2026-08-26T15:10:59-04:00

rts: refactor to reduce THREADED_RTS in MSG_UPD_TSO_FLAGS

- No behavior change in this commit (well, a small optimization here
  makes us do less work if the target TSO owned by the curr. capability)
- Move all THREADED_RTS CPP needed into `updThreadFlag`
- Merge MSG_SET_TSO_FLAGS and MSG_UNSET_TSO_FLAGS into MSG_UPD_TSO_FLAGS
  plus a `set` bool field in the MessageUpdTSOFlag struct

Towards #27729

ed99b7b7

by Rodrigo Mesquita at 2026-08-26T15:10:59-04:00

rts: Fix race condition in MSG_UPD_TSO_FLAGS execution

The code for processing the MSG_UPD_TSO_FLAGS message was not taking
into consideration that the TSO's owner might have moved in between that
capability receiving the message (since it was its previous owner) and
starting to process its inbox (a point at which it was no longer the
owner)

Added Note [TSO owner may change in between Msg being sent and received]
to explain this race and the pattern used to fix this, where we just
forward the message to the new owner.

Fixes #27729

cd653714

by Alan Zimmerman at 2026-08-26T15:11:49-04:00

EPA: Uses Parsers.parseModule for exactprint tests

Parsers.parseModule is the advertised way to parse for use for exact
printing in the ghc-exactprint library. This commit updates the GHC
exact print testing to use it.

This requires moving the comment balancing that was occurring
only in the test path into the advertising parser path, so it moves
from Transforms.hs to Utils.hs.

Also update the comment adding to honour trailing annotations

d1d01fa5

by Wolfgang Jeltsch at 2026-08-27T13:17:59+03:00

Add `rethrowSTM` and improve STM-related documentation

Adding `rethrowSTM` resolves #26758.

The implementation of `rethrowSTM` is completely analogous to the one of
`rethrowIO`.

The following is established for the documentation of `throwSTM` and
`catchSTM`:

  * Both operations are directly described as analogs of their `IO`
    counterparts.

  * There is no reference to `throw` in the documentation of `throwSTM`,
    because, although such a reference is great in the documentation of
    `throwIO`, it is somewhat out of place in the documentation of
    `throwSTM`.

  * Instead of repeating part of `throwIO`’s documentation, the
    documentation of `throwSTM` just recommends using `throwSTM` instead
    of `throw` and references the corresponding arguments in the
    documentation of `throwIO`.

06fde293

by fendor at 2026-08-28T06:06:44-04:00

GHCi: Fix order of `PackageDBFlag`s for interactive home unit

`PackageDBFlag`s are stored in reverse order of cli specification.
When sorting the `PackageDBFlag`s by longest common prefix, we need thus
to reverse the package db stacks before calculating the prefix.
We make sure to reverse the package db stack for the interactive home
unit to uphold that later specified package dbs overwrite earlier ones.

Resolved and adds regression test for #27640

024c4d04

by fendor at 2026-08-28T06:07:23-04:00

Reuse the UnitIndexCache after initialising multiple home units

55326fa0

by Alan Zimmerman at 2026-08-28T06:08:03-04:00

EPA: Some Haddock processing tweaks

These changes to the Haddock postprocessing should not change
behaviour, but just bring it more closely in line with the
original, changed at 44309cd377f

And add some haddock exactprint tests to show they work.

b3ddee95

by Andreas Klebinger at 2026-08-28T13:57:46-04:00

hadrian: Deprecate quickest flavour.

It was more of a trap for new users than actually beneficial so we
deprecate it and suggest quick+no_dynamic_libs to users instead.

a1d81390

by Andreas Klebinger at 2026-08-28T13:58:37-04:00

cmm: Always favour entry block during block deduplication.

We now always keep the first block in the CmmGraph. This way we avoid
the need to update the entry info table.

Failing to do so caused #27722.

Fixes #27722.

5bd65f00

by Andreas Klebinger at 2026-08-28T13:59:16-04:00

test: FamAppCachePerf - Only collect bytes allocated. Fixes 27747

ced53ce6

by mangoiv at 2026-08-29T07:15:24-04:00

nightlies: output yaml to file only

Previously we would just output the metadata to stdout
which risks that it's clobbered by incidental debugt output.
We now output to file only.

Fixes #27511

578bd185

by Andreas Klebinger at 2026-08-29T07:16:05-04:00

Specialise: Stop looping on recursive dictionaries in interestingDict

interestingDict now doesn't look through loopbreaker unfoldings.
Doing so would cause infinite loops on certain dictionaries.

Fixes #27705.

7bf546fc

by Simon Peyton Jones at 2026-08-31T23:48:53-04:00

Never make an absent filler for a constraint type

mkAbsentFiller used isTerminatingType to decide, but that is not enough.
Consider

    class Eq a => UC a where {}

    let u :: UC Int           -- UC Int is a "non-terminating type"
        u = error "Absent"
    let e :: Eq Int           -- Eq Int is a "terminating type"
        e = $p1UC u

We clearly must not make a filler for `e`, because we speculatively
evaluate it. But speculatively evaluating `e` forces `u`, so we must not
make one for `u` either.

Asking isDictTy instead is not enough either, because it does not catch a
constraint hidden behind an unreduced type family application:

    type family F a :: Constraint
    type instance F W = TC W

    a :: F W => Int -> Int      -- (F W) argument is absent

    Oops!  Entered absent arg Arg: irred
    Type: F W

So play safe and use isPredTy: never make an absent filler for any
constraint-kinded type.

Fixes #27627

5f474953

by Zubin Duggal at 2026-08-31T23:48:53-04:00

Add tests for absent fillers at dictionary types

T27627   a unary class whose superclass is a non-unary class
T27627a  ...whose superclass is a Constraint-kinded type family
T27627b  ...whose superclass is a quantified constraint
T27627c  a unary class applied to itself, (UC (UC (TC a)))
T27627e  a (forall b. P b) dictionary that loops

cd5c6bcc

by Zubin Duggal at 2026-08-31T23:48:53-04:00

An abstract TyCon may hide a unary class

A class declared in an hs-boot file is an AbstractTyCon inside the
module loop, and compiling the real declaration may reveal it to be a
UnaryClassTyCon.

- isTerminatingType returned True for such AbstractTyCons

- IfaceToCore set the unary flag to False in the DFunId

So we could end up speculating bottom dictionaries because inside a module
loop we see an UnaryClassTyCon as an AbstractTyCon

Use isTerminatingTyCon, which returns False for an abstract TyCon.

The Bool in DFunId is now a cache for isTerminatingTyCon, set in
mkDFunIdDetails.

Fixes #27704

abfc224a

by Zubin Duggal at 2026-08-31T23:48:53-04:00

Specialise: don't replace dead args with absent fillers

specHeader decides an argument is dead by calling isDeadBinder on a binder of
the /optimised RHS/, then applies the filler to the /stable unfolding/
template instead. The two may differ, so the argument can be dead in
the RHS and not in the template.

The specialised function's unfolding then has an absent filler, and any call
site that inlines it evaluates the error thunk.

Dropping dead args in the specialiser is rarely worth it, to quote Simon,
"The later worker/wrapper pass will pick up the dead arg later if it is really dead. Keeps the specialiser simpler."

So instead of trying to check if the arg really is dead in the stable unfolding,
just drop the logic for dropping dead args in the specialiser altogeher.

Fixes #27703

1557fd1c

by Zubin Duggal at 2026-08-31T23:48:53-04:00

CorePrep: don't speculate a call across an hs-boot edge

We take care not to evaluate things that might be bottom, like a
looping dictionary group, but our analysis is defeated by boot files.
We only track recursion within a module, so two dictionaries that
depend on each other across a module loop each look non-recursive, and
we might speculate them.

Any recursion we cannot see must cross an hs-boot edge, so refuse to
speculate calls that cross one.

Fixes #27717

4117e5ae

by Wolfgang Jeltsch at 2026-08-31T23:49:35-04:00

Incorporate the `rethrowSTM` reexport into the `stm` submodule

4bfbf5c8

by ARATA Mizuki at 2026-09-01T18:55:08-04:00

testsuite: Fix out-of-bounds access in T3586

unsafeRead and unsafeWrite use 0-based index.

Looking at #3586, the expected output seems to be 2.8e8.

Addresses #27596

3f9db6d4

by ARATA Mizuki at 2026-09-01T18:55:08-04:00

testsuite: Fix out-of-bounds access in T21305

writeInt64Array# takes an index measured in units of Int64 elements.

Fixes #27596

44d7788f

by Simon Peyton Jones at 2026-09-01T18:55:53-04:00

Fix buglet in INLINE-arity calculation for pattern synonyms

This fixes #27744.

The buglet was accidentally introduced by

  commit 3a0f9a51c1dacc474c7fd128082edd8bf4081256
  Author: Simon Peyton Jones <simon.peytonjones@gmail.com>
  Date:   Sat Aug 1 00:13:02 2026 +0100

    Fix three bugs related to required type args and INLINE pragmas

I failed to find all the calls to `addInlinePragArity`!

df058f1d

by Simon Jakobi at 2026-09-02T07:18:06-04:00

testsuite: Migrate perf tests off collect_compiler_stats('all')

The 'all' metric argument applies a single tolerance to bytes
allocated, max_bytes_used and peak_megabytes_allocated, although their
noise profiles are incompatible (#27653): allocations are nearly
deterministic, residency needs 10-20%, and peak is quantized to 1 MB.
Any single tolerance is too tight for one metric or too slack for
another. This migrates the remaining users of 'all' (and of the 'all'
default) to explicit per-metric collection, ahead of removing 'all'
from the driver.

peak_megabytes_allocated is dropped everywhere: its 1 MB granularity
makes tight relative windows meaningless (#27613), and it is sensitive
to GC timing. In #27489 it drifted by -5.3% while max_bytes_used moved
by less than 0.1%. Where a test guards a memory property,
max_bytes_used covers it at byte granularity.

Where the motivating ticket was about compile-time memory
(T11545, T15304, T26425), residency remains gated via max_bytes_used,
now with a residency-appropriate tolerance.

max_bytes_used is dropped where residency was only ever an accident of
'all':

* T15630, T15630a, T20261: the underlying tickets (#15630, #20261)
  contain no memory data at all. One is a simplifier-ticks blowup and
  the other is stated entirely in allocation numbers, so the 20%
  window never had teeth.

* T21839c: #21839's measurements show residency essentially flat
  (+0.16%) while allocations moved +7%, so allocations are the
  discriminating metric. They are already gated at 1% via
  collect_compiler_runtime. The ghc/max gate had previously broken CI
  spuriously (9fd11585eb widened it from 1% to 10% for that reason).

Allocation tolerances are tightened to the testsuite's conventional 2%
where 'all' previously left them at 10-20%.

Assisted-by: Claude Fable 5

72dd2432

by Simon Jakobi at 2026-09-02T07:18:06-04:00

testsuite: Remove the 'all' metric argument of collect_stats

'all' gated bytes allocated, max_bytes_used and peak_megabytes_allocated
at a single tolerance, although their noise profiles are incompatible,
making such tests either flaky or toothless (#27653).

Closes #27653.

Assisted-by: Claude Fable 5

2228cb30

by Simon Jakobi at 2026-09-02T07:18:06-04:00

testsuite: Make the deviation argument of collect_stats mandatory

Almost every caller passes an explicit tolerance matched to the
metric's noise profile, and the silent 20% default is far slacker than
'bytes allocated' merits. Only two tests relied on it. They now state
their tolerance explicitly:

large-project gets 10%, in line with other large compile-time tests.

T9848 gets 2%: its metric is byte-for-byte deterministic across CI
jobs and platforms of a given test_env, has drifted only about 2.5%
since 2015, and the fusion failure it guards against would show up as
a roughly +30000% jump.

Assisted-by: Claude Fable 5

56291fc5

by Cheng Shao at 2026-09-02T07:18:45-04:00

autoconf/ghc-toolchain: bump llvm upper bound to support llvm 23

This commit bumps llvm upper bound to support llvm 23.

20eb3f41

by Cheng Shao at 2026-09-02T07:18:45-04:00

rts: fix compilation issues with clang 23

clang 23 has broadened `-Wall`/`-Wextra` ranges, exposing some minor
issues in the rts when building with validate flavours:

- Unused locals
- `#pragma GCC diagnostic pop` mismatch

This commit fixes those.

9e7739ab

by Simon Jakobi at 2026-09-03T13:45:43-04:00

Add -Wimplicit-field-strictness (#16836)

This opt-in warning fires when a data constructor field lacks an
explicit strictness annotation (`!` or `~`).  It complements the
LazyFieldAnnotations extension (4762a8bf30f) from GHC proposal 752,
which makes `~` annotations available for this purpose.

Deciding which fields to report requires their levity, so the check
runs after typechecking.  To keep the noise down, the diagnostic is
emitted once per data declaration, grouped by constructor.

Closes #16836.

Assisted-by: Claude Fable 5

6a44d591

by mangoiv at 2026-09-03T13:46:22-04:00

simplifier: remove a bogus `assert` in `rebuild_app'` in `GHC.CoreToStg.Prep.cpeApp`.

Prior to this commit
    commit 08bc245be70d95801bc1138804ed1de9474fbdc0
    Author: sheaf <sam.derbyshire@gmail.com>
    Date:   Sat Feb 28 16:30:43 2026 +0100

    Clean up join points, casts & ticks

    This commit shores up the logic dealing with casts and ticks occurring
    in between a join point binding and a jump

any `PlaceRuntime` ticks we observed were profiling ticks, even though that
isn't necessary.
The more liberal rules in the above commit allow e.g. breakpoint ticks
(which are valid PlaceRuntime ticks) to legitimately appear in an argument
position.

Fixes #27556

eaa95a6f

by Andrei Borzenkov at 2026-09-04T08:08:40-04:00

Parentheses in prefix GADT constructors (#27423)

Updated `splitLHsGadtTy` to allow looking
through the parentheses for inner binders. General example
of a code pattern that's allowed now:

  data S a where
    MkS :: (forall a. S a)

That should work now with any combination of nested
foralls and parentheses.

We don't perform parenthesis unwrapping for record
GADT constructors in accordance with GHC Proposal #402.

To this end `con_inner_bndrs` no longer stores plain forall
telescopes: `[HsForAllTelescope pass]` is replaced with
`[LHsGadtTelescope pass]`, a new `HsArg`-style type whose
`HsGadtForAll` holds an inner telescope and whose `HsGadtPar`
holds a pair of parentheses. The parentheses carry no meaning
for renaming or type checking; the only reason to record them
is exact-printing.

Updated `pprConDecl` to improve the `parse == parse . ppr . parse`
property of GADT pretty-printing.

The pretty printer can now output code that's similar to this:

  data T a where
    MkT1 :: (forall a. T a)
    MkT2 :: forall . forall a. T a

These are special cases of inner forall binders
for prefix GADT constructors, when we have either
implicit or zero explicit outer binders.

639456a8

by Evgeny Malyshev at 2026-09-04T08:09:25-04:00

HsPat: Add spacing to unary tuple patterns

Use hsep when printing unary boxed TuplePat applications so that the
MkSolo constructor is separated from its argument. The old hcat rendered
wildcard and parenthesized arguments as MkSolo_ and MkSolo().

Add T27034 to exercise the HsPat splice-dump path with wildcard and
variable arguments, and update existing affected golden output.

Fixes #27034

Assisted-By: OpenAI Codex

2908ab36

by Simon Jakobi at 2026-09-05T07:22:17-04:00

X86 NCG: use btr/bts/btc for single-bit operations

Previously the Cmm patterns

  x & ~(1 << i)
  x | (1 << i)
  x ^ (1 << i)

compiled to mov/shl/not/and-style sequences of 3-4 instructions. Now
they compile to a single btr, bts or btc, matching what C compilers
produce.

When the bit index is a literal, constant folding has already collapsed
these patterns into ones with a literal mask, such as
x & 0xfffffeffffffffff for x & ~(1 << 40). Such masks are now also
compiled to a bit-test instruction when they don't fit in an imm32 and
would otherwise have to be loaded into a register first.

For a variable bit index, this applies only when the shift is unchecked
(uncheckedShiftL#, Data.Bits.unsafeShiftL): the bounds-checked shiftL
used by e.g. the default clearBit/setBit/complementBit implementations
wraps the shift in a bounds mask that this optimisation does not see
through. With a literal index, the bounds mask is constant-folded away,
so the checked operations benefit too.

See Note [Bit-test instructions] in GHC.CmmToAsm.X86.CodeGen.

Fixes #25233.

Assisted-by: Claude Fable 5

c673ecf0

by Simon Peyton Jones at 2026-09-05T07:22:59-04:00

Move HsStatic free-var test to typechecker

A `static` form should have no free *term* variables, but it
can have free *type* variables.  Alas, the renamer does not really know what
is a term variable and what is a type variable, because of required type
arguments. This patch moves the test to the typechecker, which does know.

Addresses #27664

5939ceaf

by sheaf at 2026-09-05T22:06:18-04:00

Windows: enforce path convention in ./configure

As detailed in Note [MSYS paths] in Hadrian.Utilities, the standing
convention (using Windows-style paths with forward slashes) is now
enforced in ./configure instead of within Hadrian, removing the need for
'cygpath' calls within Hadrian.

Fixes #26683

a6061455

by sheaf at 2026-09-05T22:06:18-04:00

Hadrian: introduce ExeSpawnPath

Specific details about the filepath used to specify the executable to
spawn with CreateProcess matters on Windows: whether we use forward or
backward slashes, a leading ./, or an absolute path changes how the
executable is found.

This commit introduces 'ExeSpawnPath' which is a path that is guaranteed
to be found when spawning a process. All command invocations now go
through this type to ensure the path has been properly sanitised.

See Note [NeedCurrentDirectoryForExePath] in Hadrian.Utilities.

The same treatment is applied to hsc2hs. Updates hsc2hs submodule.

e28313e3

by sheaf at 2026-09-05T22:07:06-04:00

Preserve tick ordering in 'tickTickedExpr'

'GHC.Core.Utils.tickTickedExpr' tries to combine a tick 't1' into an
existing stack of ticks 't2s'. There are two situations:

  1. 't1' is subsumed by a tick in 't2s': drop it.
  2. A tick in 't2s' is subsumed by 't1', say 't2'.

This commit ensures that in case (2) we keep 't1' on the outside instead
of replacing 't2' at its position in the stack. This avoids re-ordering
source notes (which was the cause of #27749).

This fixes a regression introduced in 2dadf3b0d05.

Fixes #27749

3172f557

by sheaf at 2026-09-05T22:07:06-04:00

Consistently prefer local source note ticks

GHC.Cmm.DebugBlock.cmmDebugGen (DWARF annotations) and
GHC.Stg.Debug.quickSourcePos (-finfo-table-map) both contained logic to
prioritise source note ticks from the current module.

This commit commons up this logic and propagates it to a third consumer:
IPE stack frames, in GHC.Driver.GenerateCgIPEStub.
See the new function GHC.Types.Tickish.bestSourceNote.

192be0b6

by Luite Stegeman at 2026-09-07T19:43:36-04:00

rts: fix ctoi_tuple_spill_words getting out of sync

Fix a few places that were not updating ctoi_tuple_spill_words
correctly, leading to corruption/crashes when dealing with large
unboxed tuples in bytecode:

 - captureContinuationAndAbort
 - findRetryFrameHelper/findAtomicallyFrameHelper
 - interpretBCO bci_BRK_FUN

fixes #27633

604eb43c

by Simon Jakobi at 2026-09-07T19:44:15-04:00

Hadrian: don't capture the testsuite driver's output (#27780)

a6061455d54 switched the Testsuite RunTest case from Shake's cmd to the
cmd' wrapper. cmd' always captures stdout and stderr, and since the
caller asks for Exit, it returns without dumping what it captured. As a
result the testsuite output no longer appears in CI job logs: failures,
performance metrics and the summary were lost with the job.

Use cmdExe, the uncaptured cmd, as the other plain-cmd sites in that
commit do.

Fixes #27780.

Assisted-by: Claude Fable 5.1

06eee015

by Luite Stegeman at 2026-09-08T06:03:06+02:00

rts: Fix missing memory barrier in eval_thunk_selector (#27477)

unchain_thunk_selectors() was missing an ACQUIRE_LOAD for the
indirectee, leading to segfaults and corruption during GC on
weakly-ordered architectures.

Fixes #27477

f8b2bd8f

by Alan Zimmerman at 2026-09-08T09:39:12-04:00

EPA Fix HsCmdDo exact print with comments

Exact printing of HsCmdDo was ignoring the location for the do
statements, and this is an annotation that can have comments in it.

Update it so we print the statements as a unit, including any
comments.

Also add the result of auditing that we capture comments in all needed
places, noting that the remaining Anno SrcSpan instances are benign.

430967ab