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Simon Peyton Jones pushed to branch wip/T23162-spj at Glasgow Haskell Compiler / GHC

Commits:

4038a28b
by Andreas Klebinger at 2025-10-30T12:38:52-04:00
```
Add a perf test for #26425
```

f997618e

by Andreas Klebinger at 2025-10-30T12:38:52-04:00

OccAnal: Be stricter for better compiler perf.

In particular we are now stricter:

* When combining usageDetails.
* When computing binder info.

In combineUsageDetails when combining the underlying adds we compute a
new `LocalOcc` for each entry by combining the two existing ones.

Rather than wait for those entries to be forced down the road we now
force them immediately. Speeding up T26425 by about 10% with little
effect on the common case.

We also force binders we put into the Core AST everywhere now.
Failure to do so risks leaking the occ env used to set the binders
OccInfo.

For T26425 compiler residency went down by a factor of ~10x.

Compile time also improved by a factor of ~1.6.

-------------------------
Metric Decrease:
    T18698a
    T26425
    T9233
-------------------------

5618645b

by Vladislav Zavialov at 2025-10-30T12:39:33-04:00

Fix namespace specifiers in subordinate exports (#12488)

This patch fixes an oversight in the `lookupChildrenExport` function that
caused explicit namespace specifiers of subordinate export items to be
ignored:

  module M (T (type A)) where   -- should be rejected
  data T = A

Based on the `IEWrappedName` data type, there are 5 cases to consider:
1. Unadorned name:   P(X)
2. Named default:    P(default X)
3. Pattern synonym:  P(pattern X)
4. Type name:        P(type X)
5. Data name:        P(data X)

Case 1 is already handled correctly; cases 2 and 3 are parse errors; and
it is cases 4 and 5 that we are concerned with in this patch.

Following the precedent established in `LookupExactName`, we introduce
a boolean flag in `LookupChildren` to control whether to look up in all
namespaces or in a specific one. If an export item is accompanied by an
explicit namespace specifier `type` or `data`, we restrict the lookup in
`lookupGRE` to a specific namespace.

The newly introduced diagnostic `TcRnExportedSubordinateNotFound`
provides error messages and suggestions more tailored to this context
than the previously used `reportUnboundName`.

2cc9924e

by Richard Eisenberg at 2025-10-30T17:08:32+00:00

Refactor fundep solving

This commit is a large-scale refactor of the increasingly-messy code that
handles functional dependencies.  It has virtually no effect on what compiles
but improves error messages a bit.  And it does the groundwork for #23162.

The big picture is described in
    Note [Overview of functional dependencies in type inference]
in GHC.Tc.Solver.FunDeps

* New module GHC.Tc.Solver.FunDeps contains all the fundep-handling
  code for the constraint solver.

* Fundep-equalities are solved in a nested scope; they may generate
  unifications but otherwise have no other effect.
  See GHC.Tc.Solver.FunDeps.solveFunDeps

  The nested needs to start from the Givens in the inert set, but
  not the Wanteds; hence a new function `resetInertCans`, used in
  `nestFunDepsTcS`.

* That in turn means that fundep equalities never show up in error
  messages, so the complicated FunDepOrigin tracking can all disappear.

* We need to be careful about tracking unifications, so we kick out
  constraints from the inert set after doing unifications.  Unification
  tracking has been majorly reformed: see Note [WhatUnifications] in
  GHC.Tc.Utils.Unify.

  A good consequence is that the hard-to-grok `resetUnificationFlag`
  has been replaced with a simpler use of
  `reportCoarseGrainUnifications`

Smaller things:

* Rename `FunDepEqn` to `FunDepEqns` since it contains multiple
  type equalities.

Some compile time improvement

Metrics: compile_time/bytes allocated
                          Baseline
                  Test       value      New value Change
---------------------- --------------------------------------
         T5030(normal) 173,839,232    148,115,248 -14.8% GOOD
hard_hole_fits(normal) 286,768,048    284,015,416  -1.0%

             geo. mean                             -0.2%
             minimum                              -14.8%
             maximum                               +0.3%

Metric Decrease:
    T5030

072466a4