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92c0bda2
by Simon Peyton Jones at 2025-10-22T16:47:53+01:00
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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373492f9
by Simon Peyton Jones at 2025-10-22T16:57:27+01:00
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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ba9616f3
by Simon Peyton Jones at 2025-10-22T16:57:52+01:00
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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026d33b4
by Simon Peyton Jones at 2025-10-22T16:57:52+01:00
Update debug-tracing in CallArity
No effect on behaviour, and commented out anyway
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45749c4f
by Simon Peyton Jones at 2025-10-22T16:57:52+01:00
Comments only -- remove dangling Note references
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bea7fbdf
by Simon Peyton Jones at 2025-10-22T16:57:52+01:00
Accept error message wibbles