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fcf6331e
by Richard Eisenberg at 2025-11-03T08:33:05+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
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231adc30
by Simon Peyton Jones at 2025-11-03T08:33:05+00:00
QuickLook's tcInstFun should make instantiation variables directly
tcInstFun must make "instantiation variables", not regular
unification variables, when instantiating function types. That was
previously implemented by a hack: set the /ambient/ level to QLInstTyVar.
But the hack finally bit me, when I was refactoring WhatUnifications.
And it was always wrong: see the now-expunged (TCAPP2) note.
This commit does it right, by making tcInstFun call its own
instantiation functions. That entails a small bit of duplication,
but the result is much, much cleaner.
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39d4a24b
by Simon Peyton Jones at 2025-11-03T08:33:05+00:00
Build implication for constraints from (static e)
This commit addresses #26466, by buiding an implication for the
constraints arising from a (static e) form. The implication has
a special ic_info field of StaticFormSkol, which tells the constraint
solver to use an empty set of Givens.
See (SF3) in Note [Grand plan for static forms]
in GHC.Iface.Tidy.StaticPtrTable
This commit also reinstates an `assert` in GHC.Tc.Solver.Equality.
The test `StaticPtrTypeFamily` was failing with an assertion failure,
but it now works.
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2e2aec1e
by Simon Peyton Jones at 2025-11-03T08:33:05+00:00
Comments about defaulting representation equalities
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52a4d1da
by Simon Peyton Jones at 2025-11-03T08:33:05+00:00
Improve tracking of rewriter-sets
This refactor substantially improves the treatment of so-called
"rewriter-sets" in the constraint solver.
The story is described in the rewritten
Note [Wanteds rewrite Wanteds: rewriter-sets]
in GHC.Tc.Types.Constraint
Some highlights
* Trace the free coercion holes of a filled CoercionHole,
in CoercionPlusHoles. See Note [Coercion holes] (COH5)
This avoids taking having to take the free coercion variables
of a coercion when zonking a rewrriter-set
* Many knock on changes
* Make fillCoercionHole take CoercionPlusHoles as its argument
rather than to separate arguments.
* Similarly setEqIfWanted, setWantedE, wrapUnifierAndEmit.
* Be more careful about passing the correct CoHoleSet to
`rewriteEqEvidence` and friends
* Make kickOurAfterFillingCoercionHole more clever. See
new Note [Kick out after filling a coercion hole]
Smaller matters
* Rename RewriterSet to CoHoleSet
* Add special-case helper `rewriteEqEvidenceSwapOnly`
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3e78e1ba
by Simon Peyton Jones at 2025-11-03T08:33:05+00:00
Tidy up constraint solving for foralls
* In `can_eq_nc_forall` make sure to track Givens that are used
in the nested solve step.
* Tiny missing-swap bug-fix in `lookup_eq_in_qcis`
* Fix some leftover mess from
commit 14123ee646f2b9738a917b7cec30f9d3941c13de
Author: Simon Peyton Jones <simon.peytonjones@gmail.com>
Date: Wed Aug 20 00:35:48 2025 +0100
Solve forall-constraints via an implication, again
Specifically, trySolveImplication is now dead.
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973f2c25
by Simon Peyton Jones at 2025-11-03T08:33:05+00:00
Do not treat CoercionHoles as free variables in coercions
This fixes a long-standing wart in the free-variable finder;
now CoercionHoles are no longer treated as a "free variable"
of a coercion.
I got big and unexpected performance regressions when making
this change. Turned out that CallArity didn't discover that
the free variable finder could be eta-expanded, which gave very
poor code.
So I re-used Note [The one-shot state monad trick] for Endo,
resulting in GHC.Utils.EndoOS. Very simple, big win.
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c2b8a0f9
by Simon Peyton Jones at 2025-11-03T08:33:05+00:00
Update debug-tracing in CallArity
No effect on behaviour, and commented out anyway
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9aa5ee99
by Simon Peyton Jones at 2025-11-03T08:33:28+00:00
Comments only -- remove dangling Note references
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6683f183
by Simon Peyton Jones at 2025-11-03T08:33:28+00:00
Accept error message wibbles
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3ba3d9f9
by Luite Stegeman at 2025-11-04T00:59:41-05:00
rts: fix eager black holes: record mutated closure and fix assertion
This fixes two problems with handling eager black holes, introduced
by a1de535f762bc23d4cf23a5b1853591dda12cdc9.
- the closure mutation must be recorded even for eager black holes,
since the mutator has mutated it before calling threadPaused
- The assertion that an unmarked eager black hole must be owned by
the TSO calling threadPaused is incorrect, since multiple threads
can race to claim the black hole.
fixes #26495
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593e996d
by Simon Peyton Jones at 2025-11-04T14:16:30+00:00
Eliminate duplicates lazily in PmAltConSet
Addresses #26514.
See Note [PmLits in PmAltConSet]