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70c0ad10
by Ben Gamari at 2025-08-11T14:55:06-04:00
gitlab-ci: Bump DOCKER_REV
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71cd8990
by Andreas Klebinger at 2025-08-11T15:03:00-04:00
Specialise: Improve specialisation by refactoring interestingDict
This MR addresses #26051, which concerns missed type-class specialisation.
The main payload of the MR is to completely refactor the key function
`interestingDict` in GHC.Core.Opt.Specialise
The main change is that we now also look at the structure of the
dictionary we consider specializing on, rather than only the type.
See the big `Note [Interesting dictionary arguments]`
(cherry picked from commit f707bab4936fee2d8e2edd17512b18dfa98f56da)
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bd0502a9
by Simon Peyton Jones at 2025-08-11T15:03:00-04:00
Renaming around predicate types
.. we were (as it turned out) abstracting over
type-class selectors in SPECIALISATION rules!
Wibble isEqPred
(cherry picked from commit a49eca26796851d0a63f4a7fa4afe562247b8074)
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695fc5d2
by Simon Peyton Jones at 2025-08-11T15:03:00-04:00
Refactor of Specialise.hs
This patch just tidies up `specHeader` a bit, removing one
of its many results, and adding some comments.
No change in behaviour.
Also add a few more `HasDebugCallStack` contexts.
(cherry picked from commit f80375dd4945350a1d784e436975b48b9c736eaf)
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c5eff1de
by Simon Peyton Jones at 2025-08-11T15:03:00-04:00
Improve treatment of SPECIALISE pragmas -- again!
This MR does another major refactor of the way that SPECIALISE
pragmas work, to fix #26115, #26116, #26117.
* We now /always/ solve forall-constraints in an all-or-nothing way.
See Note [Solving a Wanted forall-constraint] in GHC.Tc.Solver.Solve
This means we might have unsolved quantified constraints, which need
to be reported. See `inert_insts` in `getUnsolvedInerts`.
* I refactored the short-cut solver for type classes to work by
recursively calling the solver rather than by having a little baby
solver that kept being not clever enough.
See Note [Shortcut solving] in GHC.Tc.Solver.Dict
* I totally rewrote the desugaring of SPECIALISE pragmas, again.
The new story is in Note [Desugaring new-form SPECIALISE pragmas]
in GHC.HsToCore.Binds
Both old-form and new-form SPECIALISE pragmas now route through the same
function `dsSpec_help`. The tricky function `decomposeRuleLhs` is now used only
for user-written RULES, not for SPECIALISE pragmas.
* I improved `solveOneFromTheOther` to account for rewriter sets. Previously
it would solve a non-rewritten dict from a rewritten one. For equalities
we were already dealing with this, in
Some incidental refactoring
* A small refactor: `ebv_tcvs` in `EvBindsBar` now has a list of coercions, rather
than a set of tyvars. We just delay taking the free vars.
* GHC.Core.FVs.exprFVs now returns /all/ free vars.
Use `exprLocalFVs` for Local vars.
Reason: I wanted another variant for /evidence/ variables.
* Ues `EvId` in preference to `EvVar`. (Evidence variables are always Ids.)
Rename `isEvVar` to `isEvId`.
* I moved `inert_safehask` out of `InertCans` and into `InertSet` where it
more properly belongs.
Compiler-perf changes:
* There was a palpable bug (#26117) which this MR fixes in
newWantedEvVar, which bypassed all the subtle overlapping-Given
and shortcutting logic. (See the new `newWantedEvVar`.) Fixing this
but leads to extra dictionary bindings; they are optimised away quickly
but they made CoOpt_Read allocate 3.6% more.
* Hpapily T15164 improves.
* The net compiler-allocation change is 0.0%
Metric Decrease:
T15164
Metric Increase:
CoOpt_Read
T12425
(cherry picked from commit 1bd12371feacc52394a0e660ef9349f9e8ee1c06)
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1c578310
by Simon Peyton Jones at 2025-08-11T15:03:01-04:00
Solve forall-constraints immediately, or not at all
This MR refactors the constraint solver to solve forall-constraints immediately,
rather than emitting an implication constraint to be solved later.
The most immediate motivation was that when solving quantified constraints
in SPECIALISE pragmas, we really really don't want to leave behind half-
solved implications. Also it's in tune with the approach of the new
short-cut solver, which recursively invokes the solver.
It /also/ saves quite a bit of plumbing; e.g
- The `wl_implics` field of `WorkList` is gone,
- The types of `solveSimpleWanteds` and friends are simplified.
- An EvFun contains binding, rather than an EvBindsVar ref-cell that
will in the future contain bindings. That makes `evVarsOfTerm`
simpler. Much nicer.
It also improves error messages a bit.
All described in Note [Solving a Wanted forall-constraint] in
GHC.Tc.Solver.Solve.
One tiresome point: in the tricky case of `inferConstraintsCoerceBased`
we make a forall-constraint. This we /do/ want to partially solve, so
we can infer a suitable context. (I'd be quite happy to force the user to
write a context, bt I don't want to change behavior.) So we want to generate
an /implication/ constraint in `emitPredSpecConstraints` rather than a
/forall-constraint/ as we were doing before. Discussed in (WFA3) of
the above Note.
Incidental refactoring
* `GHC.Tc.Deriv.Infer.inferConstraints` was consulting the state monad for
the DerivEnv that the caller had just consulted. Nicer to pass it as an
argument I think, so I have done that. No change in behaviour.
(cherry picked from commit 953fd8f1dc080f1c56e3a60b4b7157456949be29)
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af1f7422
by Simon Peyton Jones at 2025-08-11T15:03:01-04:00
Remove duplicated code in Ast.hs for evTermFreeVars
This is just a tidy up.
(cherry picked from commit 6921ab42925cee4e922ec6ee8e1e509092d43918)
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33331570
by Simon Peyton Jones at 2025-08-11T15:03:01-04:00
Small tc-tracing changes only
(cherry picked from commit 1165f5871b0b065b23ff244f054ddd13ef7113e7)