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

Commits:

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.

6af3089f