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Duncan Coutts pushed to branch wip/dcoutts/io-manager-feature-bitset at Glasgow Haskell Compiler / GHC

Commits:

4e9297ea

by Simon Jakobi at 2026-09-11T08:32:45-04:00

ci: Actually pass --ignore-perf-failures to the testsuite driver

684c0018d9 changed the IGNORE_PERF_FAILURES handling to append to
RUNTEST_ARGS with bash array syntax, but the three use sites still
expand RUNTEST_ARGS as a scalar, which yields only the first array
element. The appended flag was therefore dropped in every job, so
perf improvements kept failing Marge Bot batches and master pipelines,
contrary to #19562.

Append as a string instead, matching the existing --force-colors
append in test_hadrian.

Fixes #27563.

Assisted-by: Claude Fable 5.1

4f78dfdf

by Simon Jakobi at 2026-09-11T08:33:24-04:00

testsuite: Give T26537 a 1.5x compile timeout

Its -fregs-graph compile step tends to time out in unoptimized builds
(#27188, #27776).

Assisted-by: Claude Fable 5.1

130286e3

by Alan Zimmerman at 2026-09-11T08:34:08-04:00

EPA: Remove ListBanana / ListParens from AnnListBrackets

This is a step towards making AnnList only represent
lists of items which can have either braces or layout.

a9827d13

by Simon Jakobi at 2026-09-11T18:53:32-04:00

Reject ~, UNPACK and multiplicity annotations on type data fields

Only `!` was rejected so far. `~`, UNPACK and multiplicity annotations
were silently accepted. None of them make sense at the type level, so
restriction (R3) of Note [Type data declarations] now covers all of
them.

Fixes #27732.

Assisted-by: Claude Fable 5.1

c71d5e23
by Alan Zimmerman at 2026-09-11T18:54:11-04:00
```
EPA: Add a Note for the exact print main loop
```

7a108e43

by Simon Jakobi at 2026-09-12T18:35:59-04:00

FastString: Drop mkFastStringWith's constructor callback

All three callers passed the same callback, a partial application of
mkNewFastStringShortByteString to the string being interned. That
partial application is allocated as a closure before the table lookup,
on the common hit path too, although the callback is needed only after
a miss.

Drop the parameter and call mkNewFastStringShortByteString directly
after a miss. Since nothing is passed "with" anymore, rename the
function to internSB.

Suggested by Simon PJ in #27528:
https://gitlab.haskell.org/ghc/ghc/-/work_items/27528#note_687031

Assisted-by: Claude Fable 5

82c73b22

by Alan Zimmerman at 2026-09-12T18:36:38-04:00

EPA: More targeted HsDo exact print annotation

HsDo is multi-purpose, as encoded in its HsDoFlavour field. Some of
these are in a layout context (DoExpr, MDoExpr), others are not
(ListComp, MonadComp).

We are moving towards using AnnList only in layout contexts, so we
switch the HsDo TTG annotation from holding an AnnList for this, to
holding

  Either (EpToken "[", EpToken "]") AnnList

This also allows us to trim down AnnListBrackets to only have braces
or None, thereby opening the door for unification with the existing
layout context data type EpLayout.

749d2448

by Luite Stegeman at 2026-09-15T14:07:01-04:00

rts: handle large CONSTR 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  1

Closure type 1 is CONSTR. This patch adds cases for CONSTR and
CONSTR_NOCAF.

This is the same problem as #27434 (large AP closures, fixed by
cca0d58963), which missed this case.

Fixes #27649

177d6155

by Luite Stegeman at 2026-09-15T14:07:02-04:00

testsuite: fix T27434 test with compacting GC

Ensure that the interpreter is actually run with the compacting GC

5796aa63

by Luite Stegeman at 2026-09-15T14:07:49-04:00

rts: initialise the stack frame header for mask_frame and apply_mask_frame

We must leave the stack in consistent state before jumping to
mask_frame or apply_mask_frame because they may result. Failing
to do so could lead to a crash if there were waiting exceptions.

Fixes #27651

2486cc92

by Simon Peyton Jones at 2026-09-15T14:08:36-04:00

Re-introduce the "weird SpecDict" case

In this commit

    commit f80375dd4945350a1d784e436975b48b9c736eaf
    Author: Simon Peyton Jones <simon.peytonjones@gmail.com>
    Date:   Sun Jun 29 15:26:58 2025 +0100

      Refactor of Specialise.hs

I removed a test for a dictionary with unbound type variables.  This
turned out to be wrong; see #27629.

So this MR re-introduces it.

8e09a46f

by Duncan Coutts at 2026-09-15T20:11:35-04:00

Refactor (and rename) removeFromQueues, to simplify I/O managers

Rename it to unblockAndAppendToRunQueue which better reflects what it is
intended to do.

The post-condition for unblockAndAppendToRunQueue is that the TSO is on
the run queue or it is in the process of migrating to another cap.
Previously it achieved that by always directly adding the TSO to the run
queue itself.

But this actually made things more complicated for the I/O managers,
because it meant they needed a separate code path for notifying for
cancellation compared to notifying for completion. The general
notification code would always add the TSO to the run queue itself.

So the improvement is to allow different cases in
unblockAndAppendToRunQueue to achieve the same outcome in different
ways: either directly adding to the run queue or calling helper
functions that do so themselves.

This then allows the new I/O managers to share code between the sync and
async cancellation, and to reuse their notifyIOCompletion helpers for
cancellation. This avoids a source of bugs where the completion path may
be updated but the cancellation path may be forgotten, or similarly in
future for sync/async operations.

Update all the existing in-RTS I/O managers, and the posix timeout code.

d668782c

by Duncan Coutts at 2026-09-15T20:11:35-04:00

Document that awaitCompletedTimeoutsOrIO expects an empty run queue

This was true before but implicit and not relied on much. It's better to
be explicit, and allow things to depend on it.

11d938bb

by Duncan Coutts at 2026-09-15T20:11:35-04:00

Store the I/O opcode and fd in the StgAsyncIOOp

This will be useful in several I/O managers and it is handy for logging
and debugging.

It also doesn't increase the size of the StgAsyncIOOp structure. There
was enough spare padding space already.

Update the poll I/O manager to set the new fields.

Add a helper function to convert the enum IOReadOrWrite into the enum
IOOpCode. Also change IOReadOrWrite to be an enum without a typedef, for
consistency with other enumerations in IOManager.h

bfa87882

by Duncan Coutts at 2026-09-15T20:11:36-04:00

Add a new I/O manager based on select()

Yes, this is the second such I/O manager, but it is a modern
re-implementation based on the new in-RTS I/O manager infrastructure. So
it is cleaner and faster than the old select I/O manager.

Why do we need another I/O manager based on select? Why isn't the poll()
one good enough as a baseline portable unix I/O manager? Because macOS.
Apple Inc. is why we cannot have nice things.

The man page for poll on macOS documents the fact that it does not work.
At least, it does not work for all files. Specifically, it does not work
for device files. Whereas macOS select() does work for device files.
Aaaaarg!

We _do_ want to deprecate and remove the old select I/O manager, but due to
macOS we cannot do that until we have a replacement. This is that
replacement. Until of course a nice new k-queue I/O manager arrives,
which could become the new default for macOS and FreeBSD.

Interestingly, this select I/O manager is actually faster than the poll
one, on Linix, in some circumstances: specifically when many Haskell
threads are waiting on the same fd. The poll I/O manager does O(n) work
for n threads waiting on I/O, whereas the select one does O(fds) work
for the number of fds that threads are waiting on. Usually this is 1:1,
so it's not noticable, but one can concoct extreme benchmarks to show
the difference.

8e9de15a

by Duncan Coutts at 2026-09-15T20:11:36-04:00

Minor updates in the poll I/O manager to keep in sync with select

This keeps it in sync with select one. The changes are based on code review
while implementing the new select I/O manager. The two I/O managers are so
similar in structure that it makes sense to try to minimise the diff between
them. This should aid understanding, and fixes to both in future.

222668bb

by Duncan Coutts at 2026-09-15T20:11:36-04:00

Document the new select I/O manager in the user guide

in the RTS section about I/O managers.

And add a changelog entry.

0f48735b

by Cheng Shao at 2026-09-15T20:12:23-04:00

Revert "wasm: workaround WebKit bug in dyld"

This reverts commit c9b8465c2c338176fcab9d197e9d31f4aee11f68. The
underlying webkit bug has been fixed in
https://commits.webkit.org/314219@main. Closes #27564.

809294f1

by Luite Stegeman at 2026-09-15T20:13:08-04:00

rts: make stg_threadLabelzh return a valid pointer for unlabeled threads.

This fixes a segfault in the GC caused by stg_threadLabelzh returning
a 0 pointer in a GC pointer field.

stg_threadLabelzh returns a tuple of type (# Int#, ByteArray# #). If a
thread has no label, the second field is unused. We must still return
a valid heap object pointer.

Instead of returning 0, we now return stg_DEAD_SLOT_closure.

fixes #27618

e2d57026

by Luite Stegeman at 2026-09-15T20:13:54-04:00

JS: fix selector thunk handling

fix a bug where entering a selector thunk could lead to a crash
if the selected field was still a thunk.

fixes #27788

f8a7e988