Simon Peyton Jones pushed to branch wip/T26115 at Glasgow Haskell Compiler / GHC Commits: 1b3d25dd by Simon Peyton Jones at 2025-07-21T10:51:20+01:00 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 - - - - - bdc68a92 by Simon Peyton Jones at 2025-07-21T10:54:13+01:00 Solve forall-constraints immediately, or not at all Triggered by the new short-cut solver, I realised that it is nicer to solve forall-constraints immediately, rather than emitting an implication constraint to be solved later. This is an un-forced refactoring, but it 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 It also improves error messages a bit. 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. 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. - - - - - 521af58c by Simon Peyton Jones at 2025-07-21T10:54:13+01:00 Remove duplicated code in Ast.hs for evTermFreeVars This is just a tidy up. - - - - - d433cb52 by Simon Peyton Jones at 2025-07-21T10:54:13+01:00 Small tc-tracing changes only - - - - - 58 changed files: - compiler/GHC/Core.hs - compiler/GHC/Core/FVs.hs - compiler/GHC/Core/Opt/Arity.hs - compiler/GHC/Core/Predicate.hs - compiler/GHC/Core/Subst.hs - compiler/GHC/HsToCore/Binds.hs - compiler/GHC/HsToCore/Errors/Ppr.hs - compiler/GHC/HsToCore/Pmc/Solver/Types.hs - compiler/GHC/Iface/Ext/Ast.hs - compiler/GHC/Tc/Deriv.hs - compiler/GHC/Tc/Deriv/Infer.hs - compiler/GHC/Tc/Deriv/Utils.hs - compiler/GHC/Tc/Errors.hs - compiler/GHC/Tc/Gen/App.hs - compiler/GHC/Tc/Gen/Expr.hs - compiler/GHC/Tc/Gen/Pat.hs - compiler/GHC/Tc/Gen/Sig.hs - compiler/GHC/Tc/Solver.hs - compiler/GHC/Tc/Solver/Default.hs - compiler/GHC/Tc/Solver/Dict.hs - compiler/GHC/Tc/Solver/Equality.hs - compiler/GHC/Tc/Solver/InertSet.hs - compiler/GHC/Tc/Solver/Monad.hs - compiler/GHC/Tc/Solver/Solve.hs - compiler/GHC/Tc/Solver/Types.hs - compiler/GHC/Tc/Types/Constraint.hs - compiler/GHC/Tc/Types/Evidence.hs - compiler/GHC/Tc/Utils/Monad.hs - compiler/GHC/Tc/Utils/TcMType.hs - compiler/GHC/Tc/Utils/Unify.hs - compiler/GHC/Tc/Validity.hs - compiler/GHC/Tc/Zonk/Type.hs - compiler/GHC/Types/Var.hs - testsuite/tests/deriving/should_compile/T20815.hs - testsuite/tests/impredicative/T17332.stderr - testsuite/tests/quantified-constraints/T15290a.stderr - testsuite/tests/quantified-constraints/T19690.stderr - testsuite/tests/quantified-constraints/T19921.stderr - testsuite/tests/quantified-constraints/T21006.stderr - + testsuite/tests/simplCore/should_compile/T26115.hs - + testsuite/tests/simplCore/should_compile/T26115.stderr - + testsuite/tests/simplCore/should_compile/T26116.hs - + testsuite/tests/simplCore/should_compile/T26116.stderr - + testsuite/tests/simplCore/should_compile/T26117.hs - + testsuite/tests/simplCore/should_compile/T26117.stderr - testsuite/tests/simplCore/should_compile/all.T - testsuite/tests/typecheck/should_compile/T12427a.stderr - testsuite/tests/typecheck/should_compile/T23171.hs - testsuite/tests/typecheck/should_compile/TcSpecPragmas.stderr - testsuite/tests/typecheck/should_fail/T14605.hs - testsuite/tests/typecheck/should_fail/T14605.stderr - testsuite/tests/typecheck/should_fail/T15801.stderr - testsuite/tests/typecheck/should_fail/T18640a.stderr - testsuite/tests/typecheck/should_fail/T18640b.stderr - testsuite/tests/typecheck/should_fail/T19627.stderr - testsuite/tests/typecheck/should_fail/T21530b.stderr - testsuite/tests/typecheck/should_fail/T22912.stderr - testsuite/tests/typecheck/should_fail/tcfail174.stderr The diff was not included because it is too large. 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