From 8b9b7dbc913b66795c283683c7fe1fb48672666d Mon Sep 17 00:00:00 2001 From: Simon Peyton Jones Date: Fri, 31 Mar 2023 11:28:54 +0100 Subject: Use the eager unifier in the constraint solver This patch continues the refactoring of the constraint solver described in #23070. The Big Deal in this patch is to call the regular, eager unifier from the constraint solver, when we want to create new equalities. This replaces the existing, unifyWanted which amounted to yet-another-unifier, so it reduces duplication of a rather subtle piece of technology. See * Note [The eager unifier] in GHC.Tc.Utils.Unify * GHC.Tc.Solver.Monad.wrapUnifierTcS I did lots of other refactoring along the way * I simplified the treatment of right hand sides that contain CoercionHoles. Now, a constraint that contains a hetero-kind CoercionHole is non-canonical, and cannot be used for rewriting or unification alike. This required me to add the ch_hertero_kind flag to CoercionHole, with consequent knock-on effects. See wrinkle (2) of `Note [Equalities with incompatible kinds]` in GHC.Tc.Solver.Equality. * I refactored the StopOrContinue type to add StartAgain, so that after a fundep improvement (for example) we can simply start the pipeline again. * I got rid of the unpleasant (and inefficient) rewriterSetFromType/Co functions. With Richard I concluded that they are never needed. * I discovered Wrinkle (W1) in Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint, and therefore now prioritise non-rewritten equalities. Quite a few error messages change, I think always for the better. Compiler runtime stays about the same, with one outlier: a 17% improvement in T17836 Metric Decrease: T17836 T18223 --- testsuite/tests/dependent/should_fail/T11471.hs | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'testsuite/tests/dependent/should_fail/T11471.hs') diff --git a/testsuite/tests/dependent/should_fail/T11471.hs b/testsuite/tests/dependent/should_fail/T11471.hs index ae09ae07bb..f9bc764f88 100644 --- a/testsuite/tests/dependent/should_fail/T11471.hs +++ b/testsuite/tests/dependent/should_fail/T11471.hs @@ -4,12 +4,14 @@ module T11471 where import GHC.Exts import Data.Proxy +import Data.Kind type family F a :: k type instance F Int = Int# -f :: Proxy a -> F a -> F a +f :: forall (a :: Type). Proxy a -> F a -> F a +-- NB: Those calls to F are (F @Type a) f _ x = x bad = f (undefined :: Proxy Int#) 3# -- cgit v1.2.1