Reduce Mod n p <= q to p <= q + 1

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 # Unreleased
 * Fix faulty lookup for `Mod` and `Div` in GHC >= 9.2
+* Reduce `Mod n p <= q` to `p <= q + 1`
 
 # 0.4.7
 * Fix Plugin silently fails when normalizing <= in GHC 9.4+ [#50](https://github.com/clash-lang/ghc-typelits-extra/issues/50)

src-ghc-9.4/GHC/TypeLits/Extra/Solver.hs

@@ -32,14 +32,14 @@ import GHC.TcPluginM.Extra
 import GHC.Builtin.Names (eqPrimTyConKey, hasKey, getUnique)
 import GHC.Builtin.Types (promotedTrueDataCon, promotedFalseDataCon)
 import GHC.Builtin.Types (boolTy, naturalTy, cTupleDataCon, cTupleTyCon)
-import GHC.Builtin.Types.Literals (typeNatDivTyCon, typeNatModTyCon, typeNatCmpTyCon)
+import GHC.Builtin.Types.Literals (typeNatAddTyCon, typeNatDivTyCon, typeNatModTyCon, typeNatCmpTyCon)
 import GHC.Core.Coercion (mkUnivCo)
 import GHC.Core.DataCon (dataConWrapId)
 import GHC.Core.Predicate (EqRel (NomEq), Pred (EqPred, IrredPred), classifyPredType)
 import GHC.Core.Reduction (Reduction(..))
 import GHC.Core.TyCon (TyCon)
 import GHC.Core.TyCo.Rep (Type (..), TyLit (..), UnivCoProvenance (PluginProv))
-import GHC.Core.Type (Kind, mkTyConApp, splitTyConApp_maybe, typeKind)
+import GHC.Core.Type (Kind, mkTyConApp, mkNumLitTy, splitTyConApp_maybe, typeKind)
 #if MIN_VERSION_ghc(9,6,0)
 import GHC.Core.TyCo.Compare (eqType)
 #else
@@ -181,7 +181,12 @@ simplifyExtra defs eqs = tcPluginTrace "simplifyExtra" (ppr eqs) >> simples [] [
           | otherwise     -> return  (Impossible eq)
         (p, Max x y)
           | b && (p == x || p == y) -> simples (((,) <$> evMagic ct <*> pure ct):evs) news eqs'
-
+        -- transform:  Mod n p <= q
+        -- to:         p <= q + 1
+        (Mod _ p, q) | isWantedCt ct -> do
+          let succQ = toCType $ TyConApp typeNatAddTyCon [reifyEOP defs q, mkNumLitTy 1]
+          newCt <- createWantedFromNormalised defs (NatInequality ct p succQ b norm)
+          simples (((,) <$> evMagic ct <*> pure ct):evs) (newCt:news) eqs'
         -- transform:  q ~ Max x y => (p <=? q ~ True)
         -- to:         (p <=? Max x y) ~ True
         -- and try to solve that along with the rest of the eqs'

src-pre-ghc-9.4/GHC/TypeLits/Extra/Solver.hs

@@ -42,15 +42,15 @@ import GHC.Builtin.Types (boolTy, naturalTy)
 #else
 import GHC.Builtin.Types (typeNatKind)
 #endif
-import GHC.Builtin.Types.Literals (typeNatDivTyCon, typeNatModTyCon)
+import GHC.Builtin.Types.Literals (typeNatAddTyCon, typeNatDivTyCon, typeNatModTyCon)
 #if MIN_VERSION_ghc(9,2,0)
 import GHC.Builtin.Types.Literals (typeNatCmpTyCon)
 #else
 import GHC.Builtin.Types.Literals (typeNatLeqTyCon)
 #endif
 import GHC.Core.Predicate (EqRel (NomEq), Pred (EqPred), classifyPredType)
 import GHC.Core.TyCo.Rep (Type (..))
-import GHC.Core.Type (Kind, eqType, mkTyConApp, splitTyConApp_maybe, typeKind)
+import GHC.Core.Type (Kind, eqType, mkNumLitTy, mkTyConApp, splitTyConApp_maybe, typeKind)
 import GHC.Data.FastString (fsLit)
 import GHC.Driver.Plugins (Plugin (..), defaultPlugin, purePlugin)
 import GHC.Tc.Plugin (TcPluginM, tcLookupTyCon, tcPluginTrace)
@@ -77,12 +77,12 @@ import PrelNames  (eqPrimTyConKey, hasKey)
 import TcEvidence (EvTerm)
 import TcPluginM  (TcPluginM, tcLookupTyCon, tcPluginTrace)
 import TcRnTypes  (TcPlugin(..), TcPluginResult (..))
-import Type       (Kind, eqType, mkTyConApp, splitTyConApp_maybe)
+import Type       (Kind, eqType, mkNumLitTy, mkTyConApp, splitTyConApp_maybe)
 import TyCoRep    (Type (..))
 import TysWiredIn (typeNatKind, promotedTrueDataCon, promotedFalseDataCon)
-import TcTypeNats (typeNatLeqTyCon)
+import TcTypeNats (typeNatAddTyCon, typeNatLeqTyCon)
 #if MIN_VERSION_ghc(8,4,0)
-import TcTypeNats (typeNatDivTyCon, typeNatModTyCon)
+import TcTypeNats (typeNatAddTyCon, typeNatDivTyCon, typeNatModTyCon)
 #else
 import TcPluginM  (zonkCt)
 #endif
@@ -209,7 +209,12 @@ simplifyExtra defs eqs = tcPluginTrace "simplifyExtra" (ppr eqs) >> simples [] [
           | otherwise     -> return  (Impossible eq)
         (p, Max x y)
           | b && (p == x || p == y) -> simples (((,) <$> evMagic ct <*> pure ct):evs) news eqs'
-
+        -- transform:  Mod n p <= q
+        -- to:         p <= q + 1
+        (Mod _ p, q) | isWantedCt ct -> do
+          let succQ = toCType $ TyConApp typeNatAddTyCon [reifyEOP defs q, mkNumLitTy 1]
+          newCt <- createWantedFromNormalised defs (NatInequality ct p succQ b norm)
+          simples (((,) <$> evMagic ct <*> pure ct):evs) (newCt:news) eqs'
         -- transform:  q ~ Max x y => (p <=? q ~ True)
         -- to:         (p <=? Max x y) ~ True
         -- and try to solve that along with the rest of the eqs'

src/GHC/TypeLits/Extra/Solver/Unify.hs

@@ -11,6 +11,7 @@ module GHC.TypeLits.Extra.Solver.Unify
   ( ExtraDefs (..)
   , UnifyResult (..)
   , NormaliseResult
+  , toCType
   , normaliseNat
   , unifyExtra
   )
@@ -60,6 +61,8 @@ mergeNormResWith f x y = do
   (res, n3) <- f x' y'
   pure (res, n1 `mergeNormalised` n2 `mergeNormalised` n3)
 
+toCType :: Type -> ExtraOp
+toCType ty = C $ CType ty
 
 normaliseNat :: ExtraDefs -> Type -> MaybeT TcPluginM NormaliseResult
 normaliseNat defs ty | Just ty1 <- coreView ty = normaliseNat defs ty1
@@ -105,9 +108,9 @@ normaliseNat defs (TyConApp tc tys) = do
   normResults <- lift (sequence (runMaybeT . normaliseNat defs <$> tys))
   let anyNormalised = foldr mergeNormalised Untouched (snd <$> catMaybes normResults)
   let tys' = mergeExtraOp (zip normResults tys)
-  pure (C (CType (TyConApp tc tys')), anyNormalised)
+  pure (toCType $ TyConApp tc tys', anyNormalised)
 
-normaliseNat _ t = return (C (CType t), Untouched)
+normaliseNat _ t = return (toCType t, Untouched)
 
 -- | Result of comparing two 'SOP' terms, returning a potential substitution
 -- list under which the two terms are equal.

tests/Main.hs

@@ -234,6 +234,20 @@ test58b
   -> Proxy (Max (n+2) 1)
 test58b = test58a
 
+test59
+  :: Proxy n
+  -> Proxy p
+  -> Proxy (Mod n (p + 1) <=? p)
+  -> Proxy True
+test59 _ _ x = x
+
+test60
+  :: Proxy n
+  -> Proxy p
+  -> Proxy (Mod n (3 * p + 5) <=? (4 + p * 3))
+  -> Proxy True
+test60 _ _ x = x
+
 main :: IO ()
 main = defaultMain tests
 
@@ -411,6 +425,12 @@ tests = testGroup "ghc-typelits-natnormalise"
     , testCase "forall n p . n + 1 <= Max (n + p + 1) p" $
       show (test57 Proxy Proxy Proxy) @?=
       "Proxy"
+    , testCase "forall n p . Mod n (p + 1) <= p" $
+      show (test59 Proxy Proxy Proxy) @?=
+      "Proxy"
+    , testCase "forall n p . Mod n (3 * p + 5) <= (4 + p * 3)" $
+      show (test60 Proxy Proxy Proxy) @?=
+      "Proxy"
     ]
   , testGroup "errors"
     [ testCase "GCD 6 8 /~ 4" $ testFail1 `throws` testFail1Errors