{-
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998

\section[CoreRules]{Rewrite rules}
-}


-- | Functions for collecting together and applying rewrite rules to a module.
-- The 'CoreRule' datatype itself is declared elsewhere.
module GHC.Core.Rules (
        -- ** Looking up rules
        lookupRule,

        -- ** RuleBase, RuleEnv
        RuleBase, RuleEnv(..), mkRuleEnv, emptyRuleEnv,
        updExternalPackageRules, addLocalRules, updLocalRules,
        emptyRuleBase, mkRuleBase, extendRuleBaseList,
        pprRuleBase,

        -- ** Checking rule applications
        ruleCheckProgram,

        -- ** Manipulating 'RuleInfo' rules
        extendRuleInfo, addRuleInfo,
        addIdSpecialisations, addRulesToId,

        -- ** RuleBase and RuleEnv

        -- * Misc. CoreRule helpers
        rulesOfBinds, getRules, pprRulesForUser,

        -- * Making rules
        mkRule, mkSpecRule, roughTopNames

    ) where

import GHC.Prelude

import GHC.Unit.Module   ( Module )
import GHC.Unit.Module.Env
import GHC.Unit.Module.ModGuts( ModGuts(..) )
import GHC.Unit.Module.Deps( Dependencies(..) )

import GHC.Driver.DynFlags( DynFlags )
import GHC.Driver.Ppr( showSDoc )

import GHC.Core         -- All of it
import GHC.Core.Subst
import GHC.Core.SimpleOpt ( exprIsLambda_maybe )
import GHC.Core.FVs       ( exprFreeVars, exprsFreeVars, bindFreeVars
                          , rulesFreeVarsDSet, exprsOrphNames )
import GHC.Core.Utils     ( exprType, mkTick, mkTicks
                          , stripTicksTopT, stripTicksTopE
                          , isJoinBind, mkCastMCo )
import GHC.Core.Ppr       ( pprRules )
import GHC.Core.Unify as Unify ( ruleMatchTyKiX )
import GHC.Core.Type as Type
   ( Type, extendTvSubst, extendCvSubst
   , substTy, getTyVar_maybe )
import GHC.Core.TyCo.Ppr( pprParendType )
import GHC.Core.Coercion as Coercion
import GHC.Core.Tidy     ( tidyRules )
import GHC.Core.Map.Expr ( eqCoreExpr )
import GHC.Core.Opt.Arity( etaExpandToJoinPointRule )
import GHC.Core.Make     ( mkCoreLams )
import GHC.Core.Opt.OccurAnal( occurAnalyseExpr )

import GHC.Tc.Utils.TcType  ( tcSplitTyConApp_maybe )
import GHC.Builtin.Types    ( anyTypeOfKind )

import GHC.Types.Id
import GHC.Types.Id.Info ( RuleInfo( RuleInfo ) )
import GHC.Types.Var
import GHC.Types.Var.Env
import GHC.Types.Var.Set
import GHC.Types.Name    ( Name, NamedThing(..), nameIsLocalOrFrom )
import GHC.Types.Name.Set
import GHC.Types.Name.Env
import GHC.Types.Name.Occurrence( occNameFS )
import GHC.Types.Unique.FM
import GHC.Types.Tickish
import GHC.Types.Basic

import GHC.Data.FastString
import GHC.Data.Maybe
import GHC.Data.Bag
import GHC.Data.List.SetOps( hasNoDups )

import GHC.Utils.Misc as Utils
import GHC.Utils.Outputable
import GHC.Utils.Panic
import GHC.Utils.Constants (debugIsOn)

import Data.List (sortBy, mapAccumL, isPrefixOf)
import Data.Function    ( on )
import Control.Monad    ( guard )

{-
Note [Overall plumbing for rules]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* After the desugarer:
   - The ModGuts initially contains mg_rules :: [CoreRule] of
     locally-declared rules for imported Ids.
   - Locally-declared rules for locally-declared Ids are attached to
     the IdInfo for that Id.  See Note [Attach rules to local ids] in
     GHC.HsToCore.Binds

* GHC.Iface.Tidy strips off all the rules from local Ids and adds them to
  mg_rules, so that the ModGuts has *all* the locally-declared rules.

* The HomePackageTable contains a ModDetails for each home package
  module.  Each contains md_rules :: [CoreRule] of rules declared in
  that module.  The HomePackageTable grows as ghc --make does its
  up-sweep.  In batch mode (ghc -c), the HPT is empty; all imported modules
  are treated by the "external" route, discussed next, regardless of
  which package they come from.

* The ExternalPackageState has a single eps_rule_base :: RuleBase for
  Ids in other packages.  This RuleBase simply grow monotonically, as
  ghc --make compiles one module after another.

  During simplification, interface files may get demand-loaded,
  as the simplifier explores the unfoldings for Ids it has in
  its hand.  (Via an unsafePerformIO; the EPS is really a cache.)
  That in turn may make the EPS rule-base grow.  In contrast, the
  HPT never grows in this way.

* The result of all this is that during Core-to-Core optimisation
  there are four sources of rules:

    (a) Rules in the IdInfo of the Id they are a rule for.  These are
        easy: fast to look up, and if you apply a substitution then
        it'll be applied to the IdInfo as a matter of course.

    (b) Rules declared in this module for imported Ids, kept in the
        ModGuts. If you do a substitution, you'd better apply the
        substitution to these.  There are seldom many of these.

    (c) Rules declared in the HomePackageTable.  These never change.

    (d) Rules in the ExternalPackageTable. These can grow in response
        to lazy demand-loading of interfaces.

* At the moment (c) is carried in a reader-monad way by the GHC.Core.Opt.Monad.
  The HomePackageTable doesn't have a single RuleBase because technically
  we should only be able to "see" rules "below" this module; so we
  generate a RuleBase for (c) by combining rules from all the modules
  "below" us.  That's why we can't just select the home-package RuleBase
  from HscEnv.

  [NB: we are inconsistent here.  We should do the same for external
  packages, but we don't.  Same for type-class instances.]

* So in the outer simplifier loop (simplifyPgmIO), we combine (b & c) into a single
  RuleBase, reading
     (b) from the ModGuts,
     (c) from the GHC.Core.Opt.Monad, and
  just before doing rule matching we read
     (d) from its mutable variable
  and combine it with the results from (b & c).

  In a single simplifier run new rules can be added into the EPS so it matters
  to keep an up-to-date view of which rules have been loaded. For examples of
  where this went wrong and caused cryptic performance regressions
  see T19790 and !6735.


************************************************************************
*                                                                      *
\subsection[specialisation-IdInfo]{Specialisation info about an @Id@}
*                                                                      *
************************************************************************

A CoreRule holds details of one rule for an Id, which
includes its specialisations.

For example, if a rule for f is
   RULE "f" forall @a @b d. f @(List a) @b d = f' a b

then when we find an application of f to matching types, we simply replace
it by the matching RHS:
        f (List Int) Bool dict ===>  f' Int Bool
All the stuff about how many dictionaries to discard, and what types
to apply the specialised function to, are handled by the fact that the
Rule contains a template for the result of the specialisation.
-}

mkRule :: Module -> Bool -> Bool -> RuleName -> Activation
       -> Name -> [CoreBndr] -> [CoreExpr] -> CoreExpr -> CoreRule
-- ^ Used to make 'CoreRule' for an 'Id' defined in the module being
-- compiled. See also 'GHC.Core.CoreRule'
mkRule :: Module
-> Bool
-> Bool
-> RuleName
-> Activation
-> Name
-> [Var]
-> [CoreExpr]
-> CoreExpr
-> CoreRule
mkRule Module
this_mod Bool
is_auto Bool
is_local RuleName
name Activation
act Name
fn [Var]
bndrs [CoreExpr]
args CoreExpr
rhs
  = Rule { ru_name :: RuleName
ru_name   = RuleName
name
         , ru_act :: Activation
ru_act    = Activation
act
         , ru_fn :: Name
ru_fn     = Name
fn
         , ru_bndrs :: [Var]
ru_bndrs  = [Var]
bndrs
         , ru_args :: [CoreExpr]
ru_args   = [CoreExpr]
args
         , ru_rhs :: CoreExpr
ru_rhs    = CoreExpr -> CoreExpr
occurAnalyseExpr CoreExpr
rhs
                       -- See Note [OccInfo in unfoldings and rules]
         , ru_rough :: [Maybe Name]
ru_rough  = [CoreExpr] -> [Maybe Name]
roughTopNames [CoreExpr]
args
         , ru_origin :: Module
ru_origin = Module
this_mod
         , ru_orphan :: IsOrphan
ru_orphan = IsOrphan
orph
         , ru_auto :: Bool
ru_auto   = Bool
is_auto
         , ru_local :: Bool
ru_local  = Bool
is_local }
  where
        -- Compute orphanhood.  See Note [Orphans] in GHC.Core.InstEnv
        -- A rule is an orphan only if none of the variables
        -- mentioned on its left-hand side are locally defined
    lhs_names :: NameSet
lhs_names = NameSet -> Name -> NameSet
extendNameSet ([CoreExpr] -> NameSet
exprsOrphNames [CoreExpr]
args) Name
fn

        -- Since rules get eventually attached to one of the free names
        -- from the definition when compiling the ABI hash, we should make
        -- it deterministic. This chooses the one with minimal OccName
        -- as opposed to uniq value.
    local_lhs_names :: NameSet
local_lhs_names = (Name -> Bool) -> NameSet -> NameSet
filterNameSet (Module -> Name -> Bool
nameIsLocalOrFrom Module
this_mod) NameSet
lhs_names
    orph :: IsOrphan
orph = NameSet -> IsOrphan
chooseOrphanAnchor NameSet
local_lhs_names

--------------
mkSpecRule :: DynFlags -> Module -> Bool -> Activation -> SDoc
           -> Id -> [CoreBndr] -> [CoreExpr] -> CoreExpr -> CoreRule
-- Make a specialisation rule, for Specialise or SpecConstr
mkSpecRule :: DynFlags
-> Module
-> Bool
-> Activation
-> SDoc
-> Var
-> [Var]
-> [CoreExpr]
-> CoreExpr
-> CoreRule
mkSpecRule DynFlags
dflags Module
this_mod Bool
is_auto Activation
inl_act SDoc
herald Var
fn [Var]
bndrs [CoreExpr]
args CoreExpr
rhs
  = case Var -> Maybe Arity
isJoinId_maybe Var
fn of
      Just Arity
join_arity -> Arity -> CoreRule -> CoreRule
etaExpandToJoinPointRule Arity
join_arity CoreRule
rule
      Maybe Arity
Nothing         -> CoreRule
rule
  where
    rule :: CoreRule
rule = Module
-> Bool
-> Bool
-> RuleName
-> Activation
-> Name
-> [Var]
-> [CoreExpr]
-> CoreExpr
-> CoreRule
mkRule Module
this_mod Bool
is_auto Bool
is_local
                  RuleName
rule_name
                  Activation
inl_act       -- Note [Auto-specialisation and RULES]
                  (Var -> Name
idName Var
fn)
                  [Var]
bndrs [CoreExpr]
args CoreExpr
rhs

    is_local :: Bool
is_local = Var -> Bool
isLocalId Var
fn
    rule_name :: RuleName
rule_name = DynFlags -> SDoc -> Var -> [CoreExpr] -> RuleName
mkSpecRuleName DynFlags
dflags SDoc
herald Var
fn [CoreExpr]
args

mkSpecRuleName :: DynFlags -> SDoc -> Id -> [CoreExpr] -> FastString
mkSpecRuleName :: DynFlags -> SDoc -> Var -> [CoreExpr] -> RuleName
mkSpecRuleName DynFlags
dflags SDoc
herald Var
fn [CoreExpr]
args
  = String -> RuleName
mkFastString (String -> RuleName) -> String -> RuleName
forall a b. (a -> b) -> a -> b
$ DynFlags -> SDoc -> String
showSDoc DynFlags
dflags (SDoc -> String) -> SDoc -> String
forall a b. (a -> b) -> a -> b
$
    SDoc
herald SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> RuleName -> SDoc
forall doc. IsLine doc => RuleName -> doc
ftext (OccName -> RuleName
occNameFS (Var -> OccName
forall a. NamedThing a => a -> OccName
getOccName Var
fn))
                     -- This name ends up in interface files, so use occNameFS.
                     -- Otherwise uniques end up there, making builds
                     -- less deterministic (See #4012 comment:61 ff)
           SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> [SDoc] -> SDoc
forall doc. IsLine doc => [doc] -> doc
hsep ((CoreExpr -> Maybe SDoc) -> [CoreExpr] -> [SDoc]
forall a b. (a -> Maybe b) -> [a] -> [b]
mapMaybe CoreExpr -> Maybe SDoc
ppr_call_key_ty [CoreExpr]
args)
  where
    ppr_call_key_ty :: CoreExpr -> Maybe SDoc
    ppr_call_key_ty :: CoreExpr -> Maybe SDoc
ppr_call_key_ty (Type Kind
ty) = case Kind -> Maybe Var
getTyVar_maybe Kind
ty of
                                  Just {} -> SDoc -> Maybe SDoc
forall a. a -> Maybe a
Just (String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"@_")
                                  Maybe Var
Nothing -> SDoc -> Maybe SDoc
forall a. a -> Maybe a
Just (SDoc -> Maybe SDoc) -> SDoc -> Maybe SDoc
forall a b. (a -> b) -> a -> b
$ Char -> SDoc
forall doc. IsLine doc => Char -> doc
char Char
'@' SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<> Kind -> SDoc
pprParendType Kind
ty
    ppr_call_key_ty CoreExpr
_ = Maybe SDoc
forall a. Maybe a
Nothing


--------------
roughTopNames :: [CoreExpr] -> [Maybe Name]
-- ^ Find the \"top\" free names of several expressions.
-- Such names are either:
--
-- 1. The function finally being applied to in an application chain
--    (if that name is a GlobalId: see "GHC.Types.Var#globalvslocal"), or
--
-- 2. The 'TyCon' if the expression is a 'Type'
--
-- This is used for the fast-match-check for rules;
--      if the top names don't match, the rest can't
roughTopNames :: [CoreExpr] -> [Maybe Name]
roughTopNames [CoreExpr]
args = (CoreExpr -> Maybe Name) -> [CoreExpr] -> [Maybe Name]
forall a b. (a -> b) -> [a] -> [b]
map CoreExpr -> Maybe Name
roughTopName [CoreExpr]
args

roughTopName :: CoreExpr -> Maybe Name
roughTopName :: CoreExpr -> Maybe Name
roughTopName (Type Kind
ty) = case HasCallStack => Kind -> Maybe (TyCon, [Kind])
Kind -> Maybe (TyCon, [Kind])
tcSplitTyConApp_maybe Kind
ty of
                               Just (TyCon
tc,[Kind]
_) -> Name -> Maybe Name
forall a. a -> Maybe a
Just (TyCon -> Name
forall a. NamedThing a => a -> Name
getName TyCon
tc)
                               Maybe (TyCon, [Kind])
Nothing     -> Maybe Name
forall a. Maybe a
Nothing
roughTopName (Coercion Coercion
_) = Maybe Name
forall a. Maybe a
Nothing
roughTopName (App CoreExpr
f CoreExpr
_) = CoreExpr -> Maybe Name
roughTopName CoreExpr
f
roughTopName (Var Var
f)   | Var -> Bool
isGlobalId Var
f   -- Note [Care with roughTopName]
                       , Var -> Bool
isDataConWorkId Var
f Bool -> Bool -> Bool
|| Var -> Arity
idArity Var
f Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
> Arity
0
                       = Name -> Maybe Name
forall a. a -> Maybe a
Just (Var -> Name
idName Var
f)
roughTopName (Tick CoreTickish
t CoreExpr
e) | CoreTickish -> Bool
forall (pass :: TickishPass). GenTickish pass -> Bool
tickishFloatable CoreTickish
t
                        = CoreExpr -> Maybe Name
roughTopName CoreExpr
e
roughTopName CoreExpr
_ = Maybe Name
forall a. Maybe a
Nothing

ruleCantMatch :: [Maybe Name] -> [Maybe Name] -> Bool
-- ^ @ruleCantMatch tpl actual@ returns True only if @actual@
-- definitely can't match @tpl@ by instantiating @tpl@.
-- It's only a one-way match; unlike instance matching we
-- don't consider unification.
--
-- Notice that [_$_]
--      @ruleCantMatch [Nothing] [Just n2] = False@
--      Reason: a template variable can be instantiated by a constant
-- Also:
--      @ruleCantMatch [Just n1] [Nothing] = False@
--      Reason: a local variable @v@ in the actuals might [_$_]

ruleCantMatch :: [Maybe Name] -> [Maybe Name] -> Bool
ruleCantMatch (Just Name
n1 : [Maybe Name]
ts) (Just Name
n2 : [Maybe Name]
as) = Name
n1 Name -> Name -> Bool
forall a. Eq a => a -> a -> Bool
/= Name
n2 Bool -> Bool -> Bool
|| [Maybe Name] -> [Maybe Name] -> Bool
ruleCantMatch [Maybe Name]
ts [Maybe Name]
as
ruleCantMatch (Maybe Name
_       : [Maybe Name]
ts) (Maybe Name
_       : [Maybe Name]
as) = [Maybe Name] -> [Maybe Name] -> Bool
ruleCantMatch [Maybe Name]
ts [Maybe Name]
as
ruleCantMatch [Maybe Name]
_              [Maybe Name]
_              = Bool
False

{-
Note [Care with roughTopName]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this
    module M where { x = a:b }
    module N where { ...f x...
                     RULE f (p:q) = ... }
You'd expect the rule to match, because the matcher can
look through the unfolding of 'x'.  So we must avoid roughTopName
returning 'M.x' for the call (f x), or else it'll say "can't match"
and we won't even try!!

However, suppose we have
         RULE g (M.h x) = ...
         foo = ...(g (M.k v))....
where k is a *function* exported by M.  We never really match
functions (lambdas) except by name, so in this case it seems like
a good idea to treat 'M.k' as a roughTopName of the call.
-}

pprRulesForUser :: [CoreRule] -> SDoc
-- (a) tidy the rules
-- (b) sort them into order based on the rule name
-- (c) suppress uniques (unless -dppr-debug is on)
-- This combination makes the output stable so we can use in testing
-- It's here rather than in GHC.Core.Ppr because it calls tidyRules
pprRulesForUser :: [CoreRule] -> SDoc
pprRulesForUser [CoreRule]
rules
  = PprStyle -> SDoc -> SDoc
withPprStyle PprStyle
defaultUserStyle (SDoc -> SDoc) -> SDoc -> SDoc
forall a b. (a -> b) -> a -> b
$
    [CoreRule] -> SDoc
pprRules ([CoreRule] -> SDoc) -> [CoreRule] -> SDoc
forall a b. (a -> b) -> a -> b
$
    (CoreRule -> CoreRule -> Ordering) -> [CoreRule] -> [CoreRule]
forall a. (a -> a -> Ordering) -> [a] -> [a]
sortBy (RuleName -> RuleName -> Ordering
lexicalCompareFS (RuleName -> RuleName -> Ordering)
-> (CoreRule -> RuleName) -> CoreRule -> CoreRule -> Ordering
forall b c a. (b -> b -> c) -> (a -> b) -> a -> a -> c
`on` CoreRule -> RuleName
ruleName) ([CoreRule] -> [CoreRule]) -> [CoreRule] -> [CoreRule]
forall a b. (a -> b) -> a -> b
$
    TidyEnv -> [CoreRule] -> [CoreRule]
tidyRules TidyEnv
emptyTidyEnv [CoreRule]
rules

{-
************************************************************************
*                                                                      *
                RuleInfo: the rules in an IdInfo
*                                                                      *
************************************************************************
-}

extendRuleInfo :: RuleInfo -> [CoreRule] -> RuleInfo
extendRuleInfo :: RuleInfo -> [CoreRule] -> RuleInfo
extendRuleInfo (RuleInfo [CoreRule]
rs1 DVarSet
fvs1) [CoreRule]
rs2
  = [CoreRule] -> DVarSet -> RuleInfo
RuleInfo ([CoreRule]
rs2 [CoreRule] -> [CoreRule] -> [CoreRule]
forall a. [a] -> [a] -> [a]
++ [CoreRule]
rs1) ([CoreRule] -> DVarSet
rulesFreeVarsDSet [CoreRule]
rs2 DVarSet -> DVarSet -> DVarSet
`unionDVarSet` DVarSet
fvs1)

addRuleInfo :: RuleInfo -> RuleInfo -> RuleInfo
addRuleInfo :: RuleInfo -> RuleInfo -> RuleInfo
addRuleInfo (RuleInfo [CoreRule]
rs1 DVarSet
fvs1) (RuleInfo [CoreRule]
rs2 DVarSet
fvs2)
  = [CoreRule] -> DVarSet -> RuleInfo
RuleInfo ([CoreRule]
rs1 [CoreRule] -> [CoreRule] -> [CoreRule]
forall a. [a] -> [a] -> [a]
++ [CoreRule]
rs2) (DVarSet
fvs1 DVarSet -> DVarSet -> DVarSet
`unionDVarSet` DVarSet
fvs2)

addIdSpecialisations :: Id -> [CoreRule] -> Id
addIdSpecialisations :: Var -> [CoreRule] -> Var
addIdSpecialisations Var
id [CoreRule]
rules
  | [CoreRule] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [CoreRule]
rules
  = Var
id
  | Bool
otherwise
  = Var -> RuleInfo -> Var
setIdSpecialisation Var
id (RuleInfo -> Var) -> RuleInfo -> Var
forall a b. (a -> b) -> a -> b
$
    RuleInfo -> [CoreRule] -> RuleInfo
extendRuleInfo (Var -> RuleInfo
idSpecialisation Var
id) [CoreRule]
rules

addRulesToId :: RuleBase -> Id -> Id
-- Add rules in the RuleBase to the rules in the Id
addRulesToId :: RuleBase -> Var -> Var
addRulesToId RuleBase
rule_base Var
bndr
  | Just [CoreRule]
rules <- RuleBase -> Name -> Maybe [CoreRule]
forall a. NameEnv a -> Name -> Maybe a
lookupNameEnv RuleBase
rule_base (Var -> Name
idName Var
bndr)
  = Var
bndr Var -> [CoreRule] -> Var
`addIdSpecialisations` [CoreRule]
rules
  | Bool
otherwise
  = Var
bndr

-- | Gather all the rules for locally bound identifiers from the supplied bindings
rulesOfBinds :: [CoreBind] -> [CoreRule]
rulesOfBinds :: [CoreBind] -> [CoreRule]
rulesOfBinds [CoreBind]
binds = (CoreBind -> [CoreRule]) -> [CoreBind] -> [CoreRule]
forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
concatMap ((Var -> [CoreRule]) -> [Var] -> [CoreRule]
forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
concatMap Var -> [CoreRule]
idCoreRules ([Var] -> [CoreRule])
-> (CoreBind -> [Var]) -> CoreBind -> [CoreRule]
forall b c a. (b -> c) -> (a -> b) -> a -> c
. CoreBind -> [Var]
forall b. Bind b -> [b]
bindersOf) [CoreBind]
binds


{-
************************************************************************
*                                                                      *
                RuleBase
*                                                                      *
************************************************************************
-}

-- | Gathers a collection of 'CoreRule's. Maps (the name of) an 'Id' to its rules
type RuleBase = NameEnv [CoreRule]
        -- The rules are unordered;
        -- we sort out any overlaps on lookup

emptyRuleBase :: RuleBase
emptyRuleBase :: RuleBase
emptyRuleBase = RuleBase
forall a. NameEnv a
emptyNameEnv

mkRuleBase :: [CoreRule] -> RuleBase
mkRuleBase :: [CoreRule] -> RuleBase
mkRuleBase [CoreRule]
rules = RuleBase -> [CoreRule] -> RuleBase
extendRuleBaseList RuleBase
emptyRuleBase [CoreRule]
rules

extendRuleBaseList :: RuleBase -> [CoreRule] -> RuleBase
extendRuleBaseList :: RuleBase -> [CoreRule] -> RuleBase
extendRuleBaseList RuleBase
rule_base [CoreRule]
new_guys
  = (RuleBase -> CoreRule -> RuleBase)
-> RuleBase -> [CoreRule] -> RuleBase
forall b a. (b -> a -> b) -> b -> [a] -> b
forall (t :: * -> *) b a.
Foldable t =>
(b -> a -> b) -> b -> t a -> b
foldl' RuleBase -> CoreRule -> RuleBase
extendRuleBase RuleBase
rule_base [CoreRule]
new_guys

extendRuleBase :: RuleBase -> CoreRule -> RuleBase
extendRuleBase :: RuleBase -> CoreRule -> RuleBase
extendRuleBase RuleBase
rule_base CoreRule
rule
  = (CoreRule -> [CoreRule] -> [CoreRule])
-> (CoreRule -> [CoreRule])
-> RuleBase
-> Name
-> CoreRule
-> RuleBase
forall a b.
(a -> b -> b) -> (a -> b) -> NameEnv b -> Name -> a -> NameEnv b
extendNameEnv_Acc (:) CoreRule -> [CoreRule]
forall a. a -> [a]
Utils.singleton RuleBase
rule_base (CoreRule -> Name
ruleIdName CoreRule
rule) CoreRule
rule

pprRuleBase :: RuleBase -> SDoc
pprRuleBase :: RuleBase -> SDoc
pprRuleBase RuleBase
rules = RuleBase -> ([[CoreRule]] -> SDoc) -> SDoc
forall key a. UniqFM key a -> ([a] -> SDoc) -> SDoc
pprUFM RuleBase
rules (([[CoreRule]] -> SDoc) -> SDoc) -> ([[CoreRule]] -> SDoc) -> SDoc
forall a b. (a -> b) -> a -> b
$ \[[CoreRule]]
rss ->
  [SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat [ [CoreRule] -> SDoc
pprRules (TidyEnv -> [CoreRule] -> [CoreRule]
tidyRules TidyEnv
emptyTidyEnv [CoreRule]
rs)
       | [CoreRule]
rs <- [[CoreRule]]
rss ]

-- | A full rule environment which we can apply rules from.  Like a 'RuleBase',
-- but it also includes the set of visible orphans we use to filter out orphan
-- rules which are not visible (even though we can see them...)
-- See Note [Orphans] in GHC.Core
data RuleEnv
    = RuleEnv { RuleEnv -> RuleBase
re_local_rules   :: !RuleBase -- Rules from this module
              , RuleEnv -> RuleBase
re_home_rules    :: !RuleBase -- Rule from the home package
                                              --   (excl this module)
              , RuleEnv -> RuleBase
re_eps_rules     :: !RuleBase -- Rules from other packages
                                              --   see Note [External package rules]
              , RuleEnv -> ModuleSet
re_visible_orphs :: !ModuleSet
              }

mkRuleEnv :: ModGuts -> RuleBase -> RuleBase -> RuleEnv
mkRuleEnv :: ModGuts -> RuleBase -> RuleBase -> RuleEnv
mkRuleEnv (ModGuts { mg_module :: ModGuts -> Module
mg_module = Module
this_mod
                   , mg_deps :: ModGuts -> Dependencies
mg_deps   = Dependencies
deps
                   , mg_rules :: ModGuts -> [CoreRule]
mg_rules  = [CoreRule]
local_rules })
          RuleBase
eps_rules RuleBase
hpt_rules
  = RuleEnv { re_local_rules :: RuleBase
re_local_rules   = [CoreRule] -> RuleBase
mkRuleBase [CoreRule]
local_rules
            , re_home_rules :: RuleBase
re_home_rules    = RuleBase
hpt_rules
            , re_eps_rules :: RuleBase
re_eps_rules     = RuleBase
eps_rules
            , re_visible_orphs :: ModuleSet
re_visible_orphs = [Module] -> ModuleSet
mkModuleSet [Module]
vis_orphs }
  where
    vis_orphs :: [Module]
vis_orphs = Module
this_mod Module -> [Module] -> [Module]
forall a. a -> [a] -> [a]
: Dependencies -> [Module]
dep_orphs Dependencies
deps

updExternalPackageRules :: RuleEnv -> RuleBase -> RuleEnv
-- Completely over-ride the external rules in RuleEnv
updExternalPackageRules :: RuleEnv -> RuleBase -> RuleEnv
updExternalPackageRules RuleEnv
rule_env RuleBase
eps_rules
  = RuleEnv
rule_env { re_eps_rules = eps_rules }

updLocalRules :: RuleEnv -> [CoreRule] -> RuleEnv
-- Completely over-ride the local rules in RuleEnv
updLocalRules :: RuleEnv -> [CoreRule] -> RuleEnv
updLocalRules RuleEnv
rule_env [CoreRule]
local_rules
  = RuleEnv
rule_env { re_local_rules = mkRuleBase local_rules }

addLocalRules :: RuleEnv -> [CoreRule] -> RuleEnv
-- Add new local rules
addLocalRules :: RuleEnv -> [CoreRule] -> RuleEnv
addLocalRules RuleEnv
rule_env [CoreRule]
rules
  = RuleEnv
rule_env { re_local_rules = extendRuleBaseList (re_local_rules rule_env) rules }

emptyRuleEnv :: RuleEnv
emptyRuleEnv :: RuleEnv
emptyRuleEnv = RuleEnv { re_local_rules :: RuleBase
re_local_rules   = RuleBase
forall a. NameEnv a
emptyNameEnv
                       , re_home_rules :: RuleBase
re_home_rules    = RuleBase
forall a. NameEnv a
emptyNameEnv
                       , re_eps_rules :: RuleBase
re_eps_rules     = RuleBase
forall a. NameEnv a
emptyNameEnv
                       , re_visible_orphs :: ModuleSet
re_visible_orphs = ModuleSet
emptyModuleSet }

getRules :: RuleEnv -> Id -> [CoreRule]
-- Given a RuleEnv and an Id, find the visible rules for that Id
-- See Note [Where rules are found]
getRules :: RuleEnv -> Var -> [CoreRule]
getRules (RuleEnv { re_local_rules :: RuleEnv -> RuleBase
re_local_rules   = RuleBase
local_rules
                  , re_home_rules :: RuleEnv -> RuleBase
re_home_rules    = RuleBase
home_rules
                  , re_eps_rules :: RuleEnv -> RuleBase
re_eps_rules     = RuleBase
eps_rules
                  , re_visible_orphs :: RuleEnv -> ModuleSet
re_visible_orphs = ModuleSet
orphs }) Var
fn

  | Just {} <- Var -> Maybe DataCon
isDataConId_maybe Var
fn   -- Short cut for data constructor workers
  = []                                -- and wrappers, which never have any rules

  | Bool
otherwise
  = Var -> [CoreRule]
idCoreRules Var
fn          [CoreRule] -> [CoreRule] -> [CoreRule]
forall a. [a] -> [a] -> [a]
++
    RuleBase -> [CoreRule]
get RuleBase
local_rules         [CoreRule] -> [CoreRule] -> [CoreRule]
forall a. [a] -> [a] -> [a]
++
    RuleBase -> [CoreRule]
find_visible RuleBase
home_rules [CoreRule] -> [CoreRule] -> [CoreRule]
forall a. [a] -> [a] -> [a]
++
    RuleBase -> [CoreRule]
find_visible RuleBase
eps_rules

  where
    fn_name :: Name
fn_name = Var -> Name
idName Var
fn
    find_visible :: RuleBase -> [CoreRule]
find_visible RuleBase
rb = (CoreRule -> Bool) -> [CoreRule] -> [CoreRule]
forall a. (a -> Bool) -> [a] -> [a]
filter (ModuleSet -> CoreRule -> Bool
ruleIsVisible ModuleSet
orphs) (RuleBase -> [CoreRule]
get RuleBase
rb)
    get :: RuleBase -> [CoreRule]
get RuleBase
rb = RuleBase -> Name -> Maybe [CoreRule]
forall a. NameEnv a -> Name -> Maybe a
lookupNameEnv RuleBase
rb Name
fn_name Maybe [CoreRule] -> [CoreRule] -> [CoreRule]
forall a. Maybe a -> a -> a
`orElse` []

ruleIsVisible :: ModuleSet -> CoreRule -> Bool
ruleIsVisible :: ModuleSet -> CoreRule -> Bool
ruleIsVisible ModuleSet
_ BuiltinRule{} = Bool
True
ruleIsVisible ModuleSet
vis_orphs Rule { ru_orphan :: CoreRule -> IsOrphan
ru_orphan = IsOrphan
orph, ru_origin :: CoreRule -> Module
ru_origin = Module
origin }
    = IsOrphan -> Bool
notOrphan IsOrphan
orph Bool -> Bool -> Bool
|| Module
origin Module -> ModuleSet -> Bool
`elemModuleSet` ModuleSet
vis_orphs

{- Note [Where rules are found]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The rules for an Id come from two places:
  (a) the ones it is born with, stored inside the Id itself (idCoreRules fn),
  (b) rules added in other modules, stored in the global RuleBase (imp_rules)

It's tempting to think that
     - LocalIds have only (a)
     - non-LocalIds have only (b)

but that isn't quite right:

     - PrimOps and ClassOps are born with a bunch of rules inside the Id,
       even when they are imported

     - The rules in GHC.Core.Opt.ConstantFold.builtinRules should be active even
       in the module defining the Id (when it's a LocalId), but
       the rules are kept in the global RuleBase

 Note [External package rules]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In Note [Overall plumbing for rules], it is explained that the final
RuleBase which we must consider is combined from 4 different sources.

During simplifier runs, the fourth source of rules is constantly being updated
as new interfaces are loaded into the EPS. Therefore just before we check to see
if any rules match we get the EPS RuleBase and combine it with the existing RuleBase
and then perform exactly 1 lookup into the new map.

It is more efficient to avoid combining the environments and store the uncombined
environments as we can instead perform 1 lookup into each environment and then combine
the results.

Essentially we use the identity:

> lookupNameEnv n (plusNameEnv_C (++) rb1 rb2)
>   = lookupNameEnv n rb1 ++ lookupNameEnv n rb2

The latter being more efficient as we don't construct an intermediate
map.
-}

{-
************************************************************************
*                                                                      *
                        Matching
*                                                                      *
************************************************************************
-}

-- | The main rule matching function. Attempts to apply all (active)
-- supplied rules to this instance of an application in a given
-- context, returning the rule applied and the resulting expression if
-- successful.
lookupRule :: RuleOpts -> InScopeEnv
           -> (Activation -> Bool)      -- When rule is active
           -> Id -- Function head
           -> [CoreExpr] -- Args
           -> [CoreRule] -- Rules
           -> Maybe (CoreRule, CoreExpr)

-- See Note [Extra args in the target]
-- See comments on matchRule
lookupRule :: RuleOpts
-> InScopeEnv
-> (Activation -> Bool)
-> Var
-> [CoreExpr]
-> [CoreRule]
-> Maybe (CoreRule, CoreExpr)
lookupRule RuleOpts
opts rule_env :: InScopeEnv
rule_env@(ISE InScopeSet
in_scope IdUnfoldingFun
_) Activation -> Bool
is_active Var
fn [CoreExpr]
args [CoreRule]
rules
  = -- pprTrace "lookupRule" (ppr fn <+> ppr args $$ ppr rules $$ ppr in_scope) $
    case [(CoreRule, CoreExpr)] -> [CoreRule] -> [(CoreRule, CoreExpr)]
go [] [CoreRule]
rules of
        []     -> Maybe (CoreRule, CoreExpr)
forall a. Maybe a
Nothing
        ((CoreRule, CoreExpr)
m:[(CoreRule, CoreExpr)]
ms) -> (CoreRule, CoreExpr) -> Maybe (CoreRule, CoreExpr)
forall a. a -> Maybe a
Just (InScopeSet
-> (Var, [CoreExpr])
-> (CoreRule, CoreExpr)
-> [(CoreRule, CoreExpr)]
-> (CoreRule, CoreExpr)
findBest InScopeSet
in_scope (Var
fn,[CoreExpr]
args') (CoreRule, CoreExpr)
m [(CoreRule, CoreExpr)]
ms)
  where
    rough_args :: [Maybe Name]
rough_args = (CoreExpr -> Maybe Name) -> [CoreExpr] -> [Maybe Name]
forall a b. (a -> b) -> [a] -> [b]
map CoreExpr -> Maybe Name
roughTopName [CoreExpr]
args

    -- Strip ticks from arguments, see Note [Tick annotations in RULE
    -- matching]. We only collect ticks if a rule actually matches -
    -- this matters for performance tests.
    args' :: [CoreExpr]
args' = (CoreExpr -> CoreExpr) -> [CoreExpr] -> [CoreExpr]
forall a b. (a -> b) -> [a] -> [b]
map ((CoreTickish -> Bool) -> CoreExpr -> CoreExpr
forall b. (CoreTickish -> Bool) -> Expr b -> Expr b
stripTicksTopE CoreTickish -> Bool
forall (pass :: TickishPass). GenTickish pass -> Bool
tickishFloatable) [CoreExpr]
args
    ticks :: [CoreTickish]
ticks = (CoreExpr -> [CoreTickish]) -> [CoreExpr] -> [CoreTickish]
forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
concatMap ((CoreTickish -> Bool) -> CoreExpr -> [CoreTickish]
forall b. (CoreTickish -> Bool) -> Expr b -> [CoreTickish]
stripTicksTopT CoreTickish -> Bool
forall (pass :: TickishPass). GenTickish pass -> Bool
tickishFloatable) [CoreExpr]
args

    go :: [(CoreRule,CoreExpr)] -> [CoreRule] -> [(CoreRule,CoreExpr)]
    go :: [(CoreRule, CoreExpr)] -> [CoreRule] -> [(CoreRule, CoreExpr)]
go [(CoreRule, CoreExpr)]
ms [] = [(CoreRule, CoreExpr)]
ms
    go [(CoreRule, CoreExpr)]
ms (CoreRule
r:[CoreRule]
rs)
      | Just CoreExpr
e <- RuleOpts
-> InScopeEnv
-> (Activation -> Bool)
-> Var
-> [CoreExpr]
-> [Maybe Name]
-> CoreRule
-> Maybe CoreExpr
matchRule RuleOpts
opts InScopeEnv
rule_env Activation -> Bool
is_active Var
fn [CoreExpr]
args' [Maybe Name]
rough_args CoreRule
r
      = [(CoreRule, CoreExpr)] -> [CoreRule] -> [(CoreRule, CoreExpr)]
go ((CoreRule
r,[CoreTickish] -> CoreExpr -> CoreExpr
mkTicks [CoreTickish]
ticks CoreExpr
e)(CoreRule, CoreExpr)
-> [(CoreRule, CoreExpr)] -> [(CoreRule, CoreExpr)]
forall a. a -> [a] -> [a]
:[(CoreRule, CoreExpr)]
ms) [CoreRule]
rs
      | Bool
otherwise
      = -- pprTrace "match failed" (ppr r $$ ppr args $$
        --   ppr [ (arg_id, unfoldingTemplate unf)
        --       | Var arg_id <- args
        --       , let unf = idUnfolding arg_id
        --       , isCheapUnfolding unf] )
        [(CoreRule, CoreExpr)] -> [CoreRule] -> [(CoreRule, CoreExpr)]
go [(CoreRule, CoreExpr)]
ms [CoreRule]
rs

findBest :: InScopeSet -> (Id, [CoreExpr])
         -> (CoreRule,CoreExpr) -> [(CoreRule,CoreExpr)] -> (CoreRule,CoreExpr)
-- All these pairs matched the expression
-- Return the pair the most specific rule
-- The (fn,args) is just for overlap reporting

findBest :: InScopeSet
-> (Var, [CoreExpr])
-> (CoreRule, CoreExpr)
-> [(CoreRule, CoreExpr)]
-> (CoreRule, CoreExpr)
findBest InScopeSet
_        (Var, [CoreExpr])
_      (CoreRule
rule,CoreExpr
ans)   [] = (CoreRule
rule,CoreExpr
ans)
findBest InScopeSet
in_scope (Var, [CoreExpr])
target (CoreRule
rule1,CoreExpr
ans1) ((CoreRule
rule2,CoreExpr
ans2):[(CoreRule, CoreExpr)]
prs)
  | InScopeSet -> CoreRule -> CoreRule -> Bool
isMoreSpecific InScopeSet
in_scope CoreRule
rule1 CoreRule
rule2 = InScopeSet
-> (Var, [CoreExpr])
-> (CoreRule, CoreExpr)
-> [(CoreRule, CoreExpr)]
-> (CoreRule, CoreExpr)
findBest InScopeSet
in_scope (Var, [CoreExpr])
target (CoreRule
rule1,CoreExpr
ans1) [(CoreRule, CoreExpr)]
prs
  | InScopeSet -> CoreRule -> CoreRule -> Bool
isMoreSpecific InScopeSet
in_scope CoreRule
rule2 CoreRule
rule1 = InScopeSet
-> (Var, [CoreExpr])
-> (CoreRule, CoreExpr)
-> [(CoreRule, CoreExpr)]
-> (CoreRule, CoreExpr)
findBest InScopeSet
in_scope (Var, [CoreExpr])
target (CoreRule
rule2,CoreExpr
ans2) [(CoreRule, CoreExpr)]
prs
  | Bool
debugIsOn = let pp_rule :: CoreRule -> SDoc
pp_rule CoreRule
rule
                      = SDoc -> SDoc -> SDoc
forall doc. IsOutput doc => doc -> doc -> doc
ifPprDebug (CoreRule -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreRule
rule)
                                   (SDoc -> SDoc
forall doc. IsLine doc => doc -> doc
doubleQuotes (RuleName -> SDoc
forall doc. IsLine doc => RuleName -> doc
ftext (CoreRule -> RuleName
ruleName CoreRule
rule)))
                in String -> SDoc -> (CoreRule, CoreExpr) -> (CoreRule, CoreExpr)
forall a. String -> SDoc -> a -> a
pprTrace String
"Rules.findBest: rule overlap (Rule 1 wins)"
                         ([SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat [ SDoc -> SDoc
forall doc. IsOutput doc => doc -> doc
whenPprDebug (SDoc -> SDoc) -> SDoc -> SDoc
forall a b. (a -> b) -> a -> b
$
                                 String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Expression to match:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> Var -> SDoc
forall a. Outputable a => a -> SDoc
ppr Var
fn
                                 SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> [SDoc] -> SDoc
forall doc. IsLine doc => [doc] -> doc
sep ((CoreExpr -> SDoc) -> [CoreExpr] -> [SDoc]
forall a b. (a -> b) -> [a] -> [b]
map CoreExpr -> SDoc
forall a. Outputable a => a -> SDoc
ppr [CoreExpr]
args)
                               , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Rule 1:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> CoreRule -> SDoc
pp_rule CoreRule
rule1
                               , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Rule 2:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> CoreRule -> SDoc
pp_rule CoreRule
rule2]) ((CoreRule, CoreExpr) -> (CoreRule, CoreExpr))
-> (CoreRule, CoreExpr) -> (CoreRule, CoreExpr)
forall a b. (a -> b) -> a -> b
$
                InScopeSet
-> (Var, [CoreExpr])
-> (CoreRule, CoreExpr)
-> [(CoreRule, CoreExpr)]
-> (CoreRule, CoreExpr)
findBest InScopeSet
in_scope (Var, [CoreExpr])
target (CoreRule
rule1,CoreExpr
ans1) [(CoreRule, CoreExpr)]
prs
  | Bool
otherwise = InScopeSet
-> (Var, [CoreExpr])
-> (CoreRule, CoreExpr)
-> [(CoreRule, CoreExpr)]
-> (CoreRule, CoreExpr)
findBest InScopeSet
in_scope (Var, [CoreExpr])
target (CoreRule
rule1,CoreExpr
ans1) [(CoreRule, CoreExpr)]
prs
  where
    (Var
fn,[CoreExpr]
args) = (Var, [CoreExpr])
target

isMoreSpecific :: InScopeSet -> CoreRule -> CoreRule -> Bool
-- The call (rule1 `isMoreSpecific` rule2)
-- sees if rule2 can be instantiated to look like rule1
-- See Note [isMoreSpecific]
isMoreSpecific :: InScopeSet -> CoreRule -> CoreRule -> Bool
isMoreSpecific InScopeSet
_        (BuiltinRule {}) CoreRule
_                = Bool
False
isMoreSpecific InScopeSet
_        (Rule {})        (BuiltinRule {}) = Bool
True
isMoreSpecific InScopeSet
in_scope (Rule { ru_bndrs :: CoreRule -> [Var]
ru_bndrs = [Var]
bndrs1, ru_args :: CoreRule -> [CoreExpr]
ru_args = [CoreExpr]
args1 })
                        (Rule { ru_bndrs :: CoreRule -> [Var]
ru_bndrs = [Var]
bndrs2, ru_args :: CoreRule -> [CoreExpr]
ru_args = [CoreExpr]
args2
                              , ru_name :: CoreRule -> RuleName
ru_name = RuleName
rule_name2, ru_rhs :: CoreRule -> CoreExpr
ru_rhs = CoreExpr
rhs2 })
  = Maybe CoreExpr -> Bool
forall a. Maybe a -> Bool
isJust (InScopeEnv
-> RuleName
-> [Var]
-> [CoreExpr]
-> [CoreExpr]
-> CoreExpr
-> Maybe CoreExpr
matchN InScopeEnv
in_scope_env
                   RuleName
rule_name2 [Var]
bndrs2 [CoreExpr]
args2 [CoreExpr]
args1 CoreExpr
rhs2)
  where
   full_in_scope :: InScopeSet
full_in_scope = InScopeSet
in_scope InScopeSet -> [Var] -> InScopeSet
`extendInScopeSetList` [Var]
bndrs1
   in_scope_env :: InScopeEnv
in_scope_env  = InScopeSet -> IdUnfoldingFun -> InScopeEnv
ISE InScopeSet
full_in_scope IdUnfoldingFun
noUnfoldingFun
                   -- noUnfoldingFun: don't expand in templates

noBlackList :: Activation -> Bool
noBlackList :: Activation -> Bool
noBlackList Activation
_ = Bool
False           -- Nothing is black listed

{- Note [isMoreSpecific]
~~~~~~~~~~~~~~~~~~~~~~~~
The call (rule1 `isMoreSpecific` rule2)
sees if rule2 can be instantiated to look like rule1.

Wrinkle:

* We take the view that a BuiltinRule is less specific than
  anything else, because we want user-defined rules to "win"
  In particular, class ops have a built-in rule, but we
  prefer any user-specific rules to win:
    eg (#4397)
       truncate :: (RealFrac a, Integral b) => a -> b
       {-# RULES "truncate/Double->Int" truncate = double2Int #-}
       double2Int :: Double -> Int
  We want the specific RULE to beat the built-in class-op rule

Note [Extra args in the target]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If we find a matching rule, we return (Just (rule, rhs)),
/but/ the rule firing has only consumed as many of the input args
as the ruleArity says.  The unused arguments are handled by the code in
GHC.Core.Opt.Simplify.tryRules, using the arity of the returned rule.

E.g. Rule "foo":  forall a b.  f p1 p2 = rhs
     Target:      f e1 e2 e3

Then lookupRule returns Just (Rule "foo", rhs), where Rule "foo"
has ruleArity 2.  The real rewrite is
        f e1 e2 e3 ==> rhs e3

You might think it'd be cleaner for lookupRule to deal with the
leftover arguments, by applying 'rhs' to them, but the main call
in the Simplifier works better as it is.  Reason: the 'args' passed
to lookupRule are the result of a lazy substitution

Historical note:

At one stage I tried to match even if there are more args in the
/template/ than the target.  I now think this is probably a bad idea.
Should the template (map f xs) match (map g)?  I think not.  For a
start, in general eta expansion wastes work.  SLPJ July 99
-}

------------------------------------
matchRule :: RuleOpts -> InScopeEnv -> (Activation -> Bool)
          -> Id -> [CoreExpr] -> [Maybe Name]
          -> CoreRule -> Maybe CoreExpr

-- If (matchRule rule args) returns Just (name,rhs)
-- then (f args) matches the rule, and the corresponding
-- rewritten RHS is rhs
--
-- The returned expression is occurrence-analysed
--
--      Example
--
-- The rule
--      forall f g x. map f (map g x) ==> map (f . g) x
-- is stored
--      CoreRule "map/map"
--               [f,g,x]                -- tpl_vars
--               [f,map g x]            -- tpl_args
--               map (f.g) x)           -- rhs
--
-- Then the expression
--      map e1 (map e2 e3) e4
-- results in a call to
--      matchRule the_rule [e1,map e2 e3,e4]
--        = Just ("map/map", (\f,g,x -> rhs) e1 e2 e3)
--
-- NB: The 'surplus' argument e4 in the input is simply dropped.
-- See Note [Extra args in the target]

matchRule :: RuleOpts
-> InScopeEnv
-> (Activation -> Bool)
-> Var
-> [CoreExpr]
-> [Maybe Name]
-> CoreRule
-> Maybe CoreExpr
matchRule RuleOpts
opts InScopeEnv
rule_env Activation -> Bool
_is_active Var
fn [CoreExpr]
args [Maybe Name]
_rough_args
          (BuiltinRule { ru_try :: CoreRule -> RuleFun
ru_try = RuleFun
match_fn })
-- Built-in rules can't be switched off, it seems
  = case RuleFun
match_fn RuleOpts
opts InScopeEnv
rule_env Var
fn [CoreExpr]
args of
        Maybe CoreExpr
Nothing   -> Maybe CoreExpr
forall a. Maybe a
Nothing
        Just CoreExpr
expr -> CoreExpr -> Maybe CoreExpr
forall a. a -> Maybe a
Just CoreExpr
expr

matchRule RuleOpts
_ InScopeEnv
rule_env Activation -> Bool
is_active Var
_ [CoreExpr]
args [Maybe Name]
rough_args
          (Rule { ru_name :: CoreRule -> RuleName
ru_name = RuleName
rule_name, ru_act :: CoreRule -> Activation
ru_act = Activation
act, ru_rough :: CoreRule -> [Maybe Name]
ru_rough = [Maybe Name]
tpl_tops
                , ru_bndrs :: CoreRule -> [Var]
ru_bndrs = [Var]
tpl_vars, ru_args :: CoreRule -> [CoreExpr]
ru_args = [CoreExpr]
tpl_args, ru_rhs :: CoreRule -> CoreExpr
ru_rhs = CoreExpr
rhs })
  | Bool -> Bool
not (Activation -> Bool
is_active Activation
act)               = Maybe CoreExpr
forall a. Maybe a
Nothing
  | [Maybe Name] -> [Maybe Name] -> Bool
ruleCantMatch [Maybe Name]
tpl_tops [Maybe Name]
rough_args = Maybe CoreExpr
forall a. Maybe a
Nothing
  | Bool
otherwise = InScopeEnv
-> RuleName
-> [Var]
-> [CoreExpr]
-> [CoreExpr]
-> CoreExpr
-> Maybe CoreExpr
matchN InScopeEnv
rule_env RuleName
rule_name [Var]
tpl_vars [CoreExpr]
tpl_args [CoreExpr]
args CoreExpr
rhs


---------------------------------------
matchN  :: InScopeEnv
        -> RuleName -> [Var] -> [CoreExpr]
        -> [CoreExpr] -> CoreExpr           -- ^ Target; can have more elements than the template
        -> Maybe CoreExpr
-- For a given match template and context, find bindings to wrap around
-- the entire result and what should be substituted for each template variable.
--
-- Fail if there are too few actual arguments from the target to match the template
--
-- See Note [Extra args in the target]
-- If there are too /many/ actual arguments, we simply ignore the
-- trailing ones, returning the result of applying the rule to a prefix
-- of the actual arguments.

matchN :: InScopeEnv
-> RuleName
-> [Var]
-> [CoreExpr]
-> [CoreExpr]
-> CoreExpr
-> Maybe CoreExpr
matchN (ISE InScopeSet
in_scope IdUnfoldingFun
id_unf) RuleName
rule_name [Var]
tmpl_vars [CoreExpr]
tmpl_es [CoreExpr]
target_es CoreExpr
rhs
  = do  { RuleSubst
rule_subst <- RuleMatchEnv
-> RuleSubst -> [CoreExpr] -> [CoreExpr] -> Maybe RuleSubst
match_exprs RuleMatchEnv
init_menv RuleSubst
emptyRuleSubst [CoreExpr]
tmpl_es [CoreExpr]
target_es
        ; let (Subst
_, [CoreExpr]
matched_es) = (Subst -> (Var, Var) -> (Subst, CoreExpr))
-> Subst -> [(Var, Var)] -> (Subst, [CoreExpr])
forall (t :: * -> *) s a b.
Traversable t =>
(s -> a -> (s, b)) -> s -> t a -> (s, t b)
mapAccumL (RuleSubst -> Subst -> (Var, Var) -> (Subst, CoreExpr)
lookup_tmpl RuleSubst
rule_subst)
                                          (InScopeSet -> Subst
mkEmptySubst InScopeSet
in_scope) ([(Var, Var)] -> (Subst, [CoreExpr]))
-> [(Var, Var)] -> (Subst, [CoreExpr])
forall a b. (a -> b) -> a -> b
$
                                [Var]
tmpl_vars [Var] -> [Var] -> [(Var, Var)]
forall a b. [a] -> [b] -> [(a, b)]
`zip` [Var]
tmpl_vars1
              bind_wrapper :: CoreExpr -> CoreExpr
bind_wrapper = RuleSubst -> CoreExpr -> CoreExpr
rs_binds RuleSubst
rule_subst
                             -- Floated bindings; see Note [Matching lets]
       ; CoreExpr -> Maybe CoreExpr
forall a. a -> Maybe a
forall (m :: * -> *) a. Monad m => a -> m a
return (CoreExpr -> CoreExpr
bind_wrapper (CoreExpr -> CoreExpr) -> CoreExpr -> CoreExpr
forall a b. (a -> b) -> a -> b
$
                 [Var] -> CoreExpr -> CoreExpr
forall b. [b] -> Expr b -> Expr b
mkLams [Var]
tmpl_vars CoreExpr
rhs CoreExpr -> [CoreExpr] -> CoreExpr
forall b. Expr b -> [Expr b] -> Expr b
`mkApps` [CoreExpr]
matched_es) }
  where
    (RnEnv2
init_rn_env, [Var]
tmpl_vars1) = (RnEnv2 -> Var -> (RnEnv2, Var))
-> RnEnv2 -> [Var] -> (RnEnv2, [Var])
forall (t :: * -> *) s a b.
Traversable t =>
(s -> a -> (s, b)) -> s -> t a -> (s, t b)
mapAccumL RnEnv2 -> Var -> (RnEnv2, Var)
rnBndrL (InScopeSet -> RnEnv2
mkRnEnv2 InScopeSet
in_scope) [Var]
tmpl_vars
                  -- See Note [Cloning the template binders]

    init_menv :: RuleMatchEnv
init_menv = RV { rv_tmpls :: VarSet
rv_tmpls = [Var] -> VarSet
mkVarSet [Var]
tmpl_vars1
                   , rv_lcl :: RnEnv2
rv_lcl   = RnEnv2
init_rn_env
                   , rv_fltR :: Subst
rv_fltR  = InScopeSet -> Subst
mkEmptySubst (RnEnv2 -> InScopeSet
rnInScopeSet RnEnv2
init_rn_env)
                   , rv_unf :: IdUnfoldingFun
rv_unf   = IdUnfoldingFun
id_unf }

    lookup_tmpl :: RuleSubst -> Subst -> (InVar,OutVar) -> (Subst, CoreExpr)
                   -- Need to return a RuleSubst solely for the benefit of mk_fake_ty
    lookup_tmpl :: RuleSubst -> Subst -> (Var, Var) -> (Subst, CoreExpr)
lookup_tmpl (RS { rs_tv_subst :: RuleSubst -> TvSubstEnv
rs_tv_subst = TvSubstEnv
tv_subst, rs_id_subst :: RuleSubst -> IdSubstEnv
rs_id_subst = IdSubstEnv
id_subst })
                Subst
tcv_subst (Var
tmpl_var, Var
tmpl_var1)
        | Var -> Bool
isId Var
tmpl_var1
        = case IdSubstEnv -> Var -> Maybe CoreExpr
forall a. VarEnv a -> Var -> Maybe a
lookupVarEnv IdSubstEnv
id_subst Var
tmpl_var1 of
            Just CoreExpr
e | Coercion Coercion
co <- CoreExpr
e
                   -> (Subst -> Var -> Coercion -> Subst
Type.extendCvSubst Subst
tcv_subst Var
tmpl_var1 Coercion
co, Coercion -> CoreExpr
forall b. Coercion -> Expr b
Coercion Coercion
co)
                   | Bool
otherwise
                   -> (Subst
tcv_subst, CoreExpr
e)
            Maybe CoreExpr
Nothing | Just Coercion
refl_co <- Var -> Maybe Coercion
isReflCoVar_maybe Var
tmpl_var1
                    , let co :: Coercion
co = (() :: Constraint) => Subst -> Coercion -> Coercion
Subst -> Coercion -> Coercion
Coercion.substCo Subst
tcv_subst Coercion
refl_co
                    -> -- See Note [Unbound RULE binders]
                       (Subst -> Var -> Coercion -> Subst
Type.extendCvSubst Subst
tcv_subst Var
tmpl_var1 Coercion
co, Coercion -> CoreExpr
forall b. Coercion -> Expr b
Coercion Coercion
co)
                    | Bool
otherwise
                    -> Var -> (Subst, CoreExpr)
unbound Var
tmpl_var

        | Bool
otherwise
        = (Subst -> Var -> Kind -> Subst
Type.extendTvSubst Subst
tcv_subst Var
tmpl_var1 Kind
ty', Kind -> CoreExpr
forall b. Kind -> Expr b
Type Kind
ty')
        where
          ty' :: Kind
ty' = case TvSubstEnv -> Var -> Maybe Kind
forall a. VarEnv a -> Var -> Maybe a
lookupVarEnv TvSubstEnv
tv_subst Var
tmpl_var1 of
                  Just Kind
ty -> Kind
ty
                  Maybe Kind
Nothing -> Kind
fake_ty   -- See Note [Unbound RULE binders]
          fake_ty :: Kind
fake_ty = Kind -> Kind
anyTypeOfKind ((() :: Constraint) => Subst -> Kind -> Kind
Subst -> Kind -> Kind
Type.substTy Subst
tcv_subst (Var -> Kind
tyVarKind Var
tmpl_var1))
                    -- This substitution is the sole reason we accumulate
                    -- TCvSubst in lookup_tmpl

    unbound :: Var -> (Subst, CoreExpr)
unbound Var
tmpl_var
       = String -> SDoc -> (Subst, CoreExpr)
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"Template variable unbound in rewrite rule" (SDoc -> (Subst, CoreExpr)) -> SDoc -> (Subst, CoreExpr)
forall a b. (a -> b) -> a -> b
$
         [SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat [ String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Variable:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> Var -> SDoc
forall a. Outputable a => a -> SDoc
ppr Var
tmpl_var SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> SDoc
dcolon SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> Kind -> SDoc
forall a. Outputable a => a -> SDoc
ppr (Var -> Kind
varType Var
tmpl_var)
              , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Rule" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> RuleName -> SDoc
pprRuleName RuleName
rule_name
              , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Rule bndrs:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> [Var] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [Var]
tmpl_vars
              , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"LHS args:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> [CoreExpr] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [CoreExpr]
tmpl_es
              , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Actual args:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> [CoreExpr] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [CoreExpr]
target_es ]

----------------------
match_exprs :: RuleMatchEnv -> RuleSubst
            -> [CoreExpr]       -- Templates
            -> [CoreExpr]       -- Targets
            -> Maybe RuleSubst
-- If the targets are longer than templates, succeed, simply ignoring
-- the leftover targets. This matters in the call in matchN.
--
-- Precondition: corresponding elements of es1 and es2 have the same
--               type, assuming earlier elements match.
-- Example:  f :: forall v. v -> blah
--   match_exprs [Type a, y::a] [Type Int, 3]
-- Then, after matching Type a against Type Int,
-- the type of (y::a) matches that of (3::Int)
match_exprs :: RuleMatchEnv
-> RuleSubst -> [CoreExpr] -> [CoreExpr] -> Maybe RuleSubst
match_exprs RuleMatchEnv
_ RuleSubst
subst [] [CoreExpr]
_
  = RuleSubst -> Maybe RuleSubst
forall a. a -> Maybe a
Just RuleSubst
subst
match_exprs RuleMatchEnv
renv RuleSubst
subst (CoreExpr
e1:[CoreExpr]
es1) (CoreExpr
e2:[CoreExpr]
es2)
  = do { RuleSubst
subst' <- RuleMatchEnv
-> RuleSubst
-> CoreExpr
-> CoreExpr
-> MCoercion
-> Maybe RuleSubst
match RuleMatchEnv
renv RuleSubst
subst CoreExpr
e1 CoreExpr
e2 MCoercion
MRefl
       ; RuleMatchEnv
-> RuleSubst -> [CoreExpr] -> [CoreExpr] -> Maybe RuleSubst
match_exprs RuleMatchEnv
renv RuleSubst
subst' [CoreExpr]
es1 [CoreExpr]
es2 }
match_exprs RuleMatchEnv
_ RuleSubst
_ [CoreExpr]
_ [CoreExpr]
_ = Maybe RuleSubst
forall a. Maybe a
Nothing


{- Note [Unbound RULE binders]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It can be the case that the binder in a rule is not actually
bound on the LHS:

* Type variables.  Type synonyms with phantom args can give rise to
  unbound template type variables.  Consider this (#10689,
  simplCore/should_compile/T10689):

    type Foo a b = b

    f :: Eq a => a -> Bool
    f x = x==x

    {-# RULES "foo" forall (x :: Foo a Char). f x = True #-}
    finkle = f 'c'

  The rule looks like
    forall (a::*) (d::Eq Char) (x :: Foo a Char).
         f (Foo a Char) d x = True

  Matching the rule won't bind 'a', and legitimately so.  We fudge by
  pretending that 'a' is bound to (Any :: *).

* Coercion variables.  On the LHS of a RULE for a local binder
  we might have
    RULE forall (c :: a~b). f (x |> c) = e
  Now, if that binding is inlined, so that a=b=Int, we'd get
    RULE forall (c :: Int~Int). f (x |> c) = e
  and now when we simplify the LHS (Simplify.simplRule) we
  optCoercion (look at the CoVarCo case) will turn that 'c' into Refl:
    RULE forall (c :: Int~Int). f (x |> <Int>) = e
  and then perhaps drop it altogether.  Now 'c' is unbound.

  It's tricky to be sure this never happens, so instead I
  say it's OK to have an unbound coercion binder in a RULE
  provided its type is (c :: t~t).  Then, when the RULE
  fires we can substitute <t> for c.

  This actually happened (in a RULE for a local function)
  in #13410, and also in test T10602.

Note [Cloning the template binders]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider the following match (example 1):
        Template:  forall x.  f x
        Target:               f (x+1)
This should succeed, because the template variable 'x' has nothing to
do with the 'x' in the target.

Likewise this one (example 2):
        Template:  forall x. f (\x.x)
        Target:              f (\y.y)

We achieve this simply by using rnBndrL to clone the template
binders if they are already in scope.

------ Historical note -------
At one point I tried simply adding the template binders to the
in-scope set /without/ cloning them, but that failed in a horribly
obscure way in #14777.  Problem was that during matching we look
up target-term variables in the in-scope set (see Note [Lookup
in-scope]).  If a target-term variable happens to name-clash with a
template variable, that lookup will find the template variable, which
is /utterly/ bogus.  In #14777, this transformed a term variable
into a type variable, and then crashed when we wanted its idInfo.
------ End of historical note -------


************************************************************************
*                                                                      *
                   The main matcher
*                                                                      *
********************************************************************* -}

data RuleMatchEnv
  = RV { RuleMatchEnv -> RnEnv2
rv_lcl   :: RnEnv2          -- Renamings for *local bindings*
                                     --   (lambda/case)
       , RuleMatchEnv -> VarSet
rv_tmpls :: VarSet          -- Template variables
                                     --   (after applying envL of rv_lcl)
       , RuleMatchEnv -> Subst
rv_fltR  :: Subst           -- Renamings for floated let-bindings
                                     --   (domain disjoint from envR of rv_lcl)
                                     -- See Note [Matching lets]
                                     -- N.B. The InScopeSet of rv_fltR is always ignored;
                                     -- see (4) in Note [Matching lets].
       , RuleMatchEnv -> IdUnfoldingFun
rv_unf :: IdUnfoldingFun
       }

{- Note [rv_lcl in RuleMatchEnv]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider matching
  Template: \x->f
  Target:   \f->f

where 'f' is free in the template. When we meet the lambdas we must
remember to rename f :-> f' in the target, as well as x :-> f
in the template.  The rv_lcl::RnEnv2 does that.

Similarly, consider matching
     Template: {a}  \b->b
     Target:        \a->3
We must rename the \a.  Otherwise when we meet the lambdas we might
substitute [b :-> a] in the template, and then erroneously succeed in
matching what looks like the template variable 'a' against 3.

So we must add the template vars to the in-scope set before starting;
see `init_menv` in `matchN`.
-}

-- * The domain of the TvSubstEnv and IdSubstEnv are the template
--   variables passed into the match.
--
-- * The BindWrapper in a RuleSubst are the bindings floated out
--   from nested matches; see the Let case of match, below
--
data RuleSubst = RS { -- Substitution; applied only to the template, not the target
                      -- Domain is the template variables
                      -- Range never includes template variables
                      RuleSubst -> TvSubstEnv
rs_tv_subst :: TvSubstEnv
                    , RuleSubst -> IdSubstEnv
rs_id_subst :: IdSubstEnv

                      -- Floated bindings
                    , RuleSubst -> CoreExpr -> CoreExpr
rs_binds    :: BindWrapper  -- Floated bindings
                    , RuleSubst -> [Var]
rs_bndrs    :: [Var]        -- Variables bound by floated lets
                    }

type BindWrapper = CoreExpr -> CoreExpr
  -- See Notes [Matching lets] and [Matching cases]
  -- we represent the floated bindings as a core-to-core function

emptyRuleSubst :: RuleSubst
emptyRuleSubst :: RuleSubst
emptyRuleSubst = RS { rs_tv_subst :: TvSubstEnv
rs_tv_subst = TvSubstEnv
forall a. VarEnv a
emptyVarEnv, rs_id_subst :: IdSubstEnv
rs_id_subst = IdSubstEnv
forall a. VarEnv a
emptyVarEnv
                    , rs_binds :: CoreExpr -> CoreExpr
rs_binds = \CoreExpr
e -> CoreExpr
e, rs_bndrs :: [Var]
rs_bndrs = [] }


{- Note [Casts in the target]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
As far as possible we don't want casts in the target to get in the way of
matching.  E.g.
* (let bind in e)  |> co
* (case e of alts) |> co
* (\ a b. f a b)   |> co

In the first two cases we want to float the cast inwards so we can match on
the let/case.  This is not important in practice because the Simplifier does
this anyway.

But the third case /is/ important: we don't want the cast to get in the way
of eta-reduction.  See Note [Cancel reflexive casts] for a real life example.

The most convenient thing is to make 'match' take an MCoercion argument, thus:

* The main matching function
      match env subst template target mco
  matches   template ~ (target |> mco)

* Invariant: typeof( subst(template) ) = typeof( target |> mco )

Note that for applications
     (e1 e2) ~ (d1 d2) |> co
where 'co' is non-reflexive, we simply fail.  You might wonder about
     (e1 e2) ~ ((d1 |> co1) d2) |> co2
but the Simplifer pushes the casts in an application to to the
right, if it can, so this doesn't really arise.

Note [Coercion arguments]
~~~~~~~~~~~~~~~~~~~~~~~~~
What if we have (f co) in the template, where the 'co' is a coercion
argument to f?  Right now we have nothing in place to ensure that a
coercion /argument/ in the template is a variable.  We really should,
perhaps by abstracting over that variable.

C.f. the treatment of dictionaries in GHC.HsToCore.Binds.decompseRuleLhs.

For now, though, we simply behave badly, by failing in match_co.
We really should never rely on matching the structure of a coercion
(which is just a proof).

Note [Casts in the template]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider the definition
  f x = e,
and SpecConstr on call pattern
  f ((e1,e2) |> co)

We'll make a RULE
   RULE forall a,b,g.  f ((a,b)|> g) = $sf a b g
   $sf a b g = e[ ((a,b)|> g) / x ]

So here is the invariant:

  In the template, in a cast (e |> co),
  the cast `co` is always a /variable/.

Matching should bind that variable to an actual coercion, so that we
can use it in $sf.  So a Cast on the LHS (the template) calls
match_co, which succeeds when the template cast is a variable -- which
it always is.  That is why match_co has so few cases.

See also
* Note [Coercion arguments]
* Note [Matching coercion variables] in GHC.Core.Unify.
* Note [Cast swizzling on rule LHSs] in GHC.Core.Opt.Simplify.Utils:
  sm_cast_swizzle is switched off in the template of a RULE
-}

----------------------
match :: RuleMatchEnv
      -> RuleSubst              -- Substitution applies to template only
      -> CoreExpr               -- Template
      -> CoreExpr               -- Target
      -> MCoercion
      -> Maybe RuleSubst

-- Postcondition (TypeInv): if matching succeeds, then
--                          typeof( subst(template) ) = typeof( target |> mco )
--     But this is /not/ a pre-condition! The types of template and target
--     may differ, see the (App e1 e2) case
--
-- Invariant (CoInv):   if mco :: ty ~ ty, then it is MRefl, not MCo co
--                      See Note [Cancel reflexive casts]
--
-- See the notes with Unify.match, which matches types
-- Everything is very similar for terms


------------------------ Ticks ---------------------
-- We look through certain ticks. See Note [Tick annotations in RULE matching]
match :: RuleMatchEnv
-> RuleSubst
-> CoreExpr
-> CoreExpr
-> MCoercion
-> Maybe RuleSubst
match RuleMatchEnv
renv RuleSubst
subst CoreExpr
e1 (Tick CoreTickish
t CoreExpr
e2) MCoercion
mco
  | CoreTickish -> Bool
forall (pass :: TickishPass). GenTickish pass -> Bool
tickishFloatable CoreTickish
t
  = RuleMatchEnv
-> RuleSubst
-> CoreExpr
-> CoreExpr
-> MCoercion
-> Maybe RuleSubst
match RuleMatchEnv
renv RuleSubst
subst' CoreExpr
e1 CoreExpr
e2 MCoercion
mco
  | Bool
otherwise
  = Maybe RuleSubst
forall a. Maybe a
Nothing
  where
    subst' :: RuleSubst
subst' = RuleSubst
subst { rs_binds = rs_binds subst . mkTick t }

match RuleMatchEnv
renv RuleSubst
subst e :: CoreExpr
e@(Tick CoreTickish
t CoreExpr
e1) CoreExpr
e2 MCoercion
mco
  | CoreTickish -> Bool
forall (pass :: TickishPass). GenTickish pass -> Bool
tickishFloatable CoreTickish
t  -- Ignore floatable ticks in rule template.
  =  RuleMatchEnv
-> RuleSubst
-> CoreExpr
-> CoreExpr
-> MCoercion
-> Maybe RuleSubst
match RuleMatchEnv
renv RuleSubst
subst CoreExpr
e1 CoreExpr
e2 MCoercion
mco
  | Bool
otherwise
  = String -> SDoc -> Maybe RuleSubst
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"Tick in rule" (CoreExpr -> SDoc
forall a. Outputable a => a -> SDoc
ppr CoreExpr
e)

------------------------ Types ---------------------
match RuleMatchEnv
renv RuleSubst
subst (Type Kind
ty1) (Type Kind
ty2) MCoercion
_mco
  = RuleMatchEnv -> RuleSubst -> Kind -> Kind -> Maybe RuleSubst
match_ty RuleMatchEnv
renv RuleSubst
subst Kind
ty1 Kind
ty2

------------------------ Coercions ---------------------
-- See Note [Coercion arguments] for why this isn't really right
match RuleMatchEnv
renv RuleSubst
subst (Coercion Coercion
co1) (Coercion Coercion
co2) MCoercion
MRefl
  = RuleMatchEnv
-> RuleSubst -> Coercion -> Coercion -> Maybe RuleSubst
match_co RuleMatchEnv
renv RuleSubst
subst Coercion
co1 Coercion
co2
  -- The MCo case corresponds to matching  co ~ (co2 |> co3)
  -- and I have no idea what to do there -- or even if it can occur
  -- Failing seems the simplest thing to do; it's certainly safe.

------------------------ Casts ---------------------
-- See Note [Casts in the template]
--     Note [Casts in the target]
--     Note [Cancel reflexive casts]

match RuleMatchEnv
renv RuleSubst
subst CoreExpr
e1 (Cast CoreExpr
e2 Coercion
co2) MCoercion
mco
  = RuleMatchEnv
-> RuleSubst
-> CoreExpr
-> CoreExpr
-> MCoercion
-> Maybe RuleSubst
match RuleMatchEnv
renv RuleSubst
subst CoreExpr
e1 CoreExpr
e2 (MCoercion -> MCoercion
checkReflexiveMCo (Coercion -> MCoercion -> MCoercion
mkTransMCoR Coercion
co2 MCoercion
mco))
    -- checkReflexiveMCo: cancel casts if possible
    -- This is important: see Note [Cancel reflexive casts]

match RuleMatchEnv
renv RuleSubst
subst (Cast CoreExpr
e1 Coercion
co1) CoreExpr
e2 MCoercion
mco
  = -- See Note [Casts in the template]
    do { let co2 :: Coercion
co2 = case MCoercion
mco of
                     MCoercion
MRefl   -> Kind -> Coercion
mkRepReflCo ((() :: Constraint) => CoreExpr -> Kind
CoreExpr -> Kind
exprType CoreExpr
e2)
                     MCo Coercion
co2 -> Coercion
co2
       ; RuleSubst
subst1 <- RuleMatchEnv
-> RuleSubst -> Coercion -> Coercion -> Maybe RuleSubst
match_co RuleMatchEnv
renv RuleSubst
subst Coercion
co1 Coercion
co2
         -- If match_co succeeds, then (exprType e1) = (exprType e2)
         -- Hence the MRefl in the next line
       ; RuleMatchEnv
-> RuleSubst
-> CoreExpr
-> CoreExpr
-> MCoercion
-> Maybe RuleSubst
match RuleMatchEnv
renv RuleSubst
subst1 CoreExpr
e1 CoreExpr
e2 MCoercion
MRefl }

------------------------ Literals ---------------------
match RuleMatchEnv
_ RuleSubst
subst (Lit Literal
lit1) (Lit Literal
lit2) MCoercion
mco
  | Literal
lit1 Literal -> Literal -> Bool
forall a. Eq a => a -> a -> Bool
== Literal
lit2
  = Bool -> SDoc -> Maybe RuleSubst -> Maybe RuleSubst
forall a. HasCallStack => Bool -> SDoc -> a -> a
assertPpr (MCoercion -> Bool
isReflMCo MCoercion
mco) (MCoercion -> SDoc
forall a. Outputable a => a -> SDoc
ppr MCoercion
mco) (Maybe RuleSubst -> Maybe RuleSubst)
-> Maybe RuleSubst -> Maybe RuleSubst
forall a b. (a -> b) -> a -> b
$
    RuleSubst -> Maybe RuleSubst
forall a. a -> Maybe a
Just RuleSubst
subst

------------------------ Variables ---------------------
-- The Var case follows closely what happens in GHC.Core.Unify.match
match RuleMatchEnv
renv RuleSubst
subst (Var Var
v1) CoreExpr
e2 MCoercion
mco
  = RuleMatchEnv -> RuleSubst -> Var -> CoreExpr -> Maybe RuleSubst
match_var RuleMatchEnv
renv RuleSubst
subst Var
v1 (CoreExpr -> MCoercion -> CoreExpr
mkCastMCo CoreExpr
e2 MCoercion
mco)

match RuleMatchEnv
renv RuleSubst
subst CoreExpr
e1 (Var Var
v2) MCoercion
mco  -- Note [Expanding variables]
  | Bool -> Bool
not (RnEnv2 -> Var -> Bool
inRnEnvR RnEnv2
rn_env Var
v2)      -- Note [Do not expand locally-bound variables]
  , Just CoreExpr
e2' <- Unfolding -> Maybe CoreExpr
expandUnfolding_maybe (RuleMatchEnv -> IdUnfoldingFun
rv_unf RuleMatchEnv
renv Var
v2')
  = RuleMatchEnv
-> RuleSubst
-> CoreExpr
-> CoreExpr
-> MCoercion
-> Maybe RuleSubst
match (RuleMatchEnv
renv { rv_lcl = nukeRnEnvR rn_env }) RuleSubst
subst CoreExpr
e1 CoreExpr
e2' MCoercion
mco
  where
    v2' :: Var
v2'    = RnEnv2 -> Var -> Var
lookupRnInScope RnEnv2
rn_env Var
v2
    rn_env :: RnEnv2
rn_env = RuleMatchEnv -> RnEnv2
rv_lcl RuleMatchEnv
renv
        -- Notice that we look up v2 in the in-scope set
        -- See Note [Lookup in-scope]
        -- No need to apply any renaming first (hence no rnOccR)
        -- because of the not-inRnEnvR

------------------------ Applications ---------------------
-- See Note [Matching higher order patterns]
match renv :: RuleMatchEnv
renv@(RV { rv_tmpls :: RuleMatchEnv -> VarSet
rv_tmpls = VarSet
tmpls, rv_lcl :: RuleMatchEnv -> RnEnv2
rv_lcl = RnEnv2
rn_env })
      RuleSubst
subst  e1 :: CoreExpr
e1@App{} CoreExpr
e2
      MCoercion
MRefl               -- Like the App case we insist on Refl here
                          -- See Note [Casts in the target]
  | (Var Var
f, [CoreExpr]
args) <- CoreExpr -> (CoreExpr, [CoreExpr])
forall b. Expr b -> (Expr b, [Expr b])
collectArgs CoreExpr
e1
  , let f' :: Var
f' = RnEnv2 -> Var -> Var
rnOccL RnEnv2
rn_env Var
f   -- See similar rnOccL in match_var
  , Var
f' Var -> VarSet -> Bool
`elemVarSet` VarSet
tmpls                     -- (HOP1)
  , Just [Var]
vs2 <- (CoreExpr -> Maybe Var) -> [CoreExpr] -> Maybe [Var]
forall (t :: * -> *) (f :: * -> *) a b.
(Traversable t, Applicative f) =>
(a -> f b) -> t a -> f (t b)
forall (f :: * -> *) a b.
Applicative f =>
(a -> f b) -> [a] -> f [b]
traverse CoreExpr -> Maybe Var
arg_as_lcl_var [CoreExpr]
args  -- (HOP2), (HOP3)
  , [Var] -> Bool
forall a. Eq a => [a] -> Bool
hasNoDups [Var]
vs2                             -- (HOP4)
  , Bool -> Bool
not Bool
can_decompose_app_instead
  = RuleMatchEnv -> RuleSubst -> Var -> CoreExpr -> Maybe RuleSubst
match_tmpl_var RuleMatchEnv
renv RuleSubst
subst Var
f' ([Var] -> CoreExpr -> CoreExpr
mkCoreLams [Var]
vs2 CoreExpr
e2)
    -- match_tmpl_var checks (HOP5) and (HOP6)
  where
    arg_as_lcl_var :: CoreExpr -> Maybe Var
    arg_as_lcl_var :: CoreExpr -> Maybe Var
arg_as_lcl_var (Var Var
v)
      | Just Var
v' <- RnEnv2 -> Var -> Maybe Var
rnOccL_maybe RnEnv2
rn_env Var
v
      , Bool -> Bool
not (Var
v' Var -> VarSet -> Bool
`elemVarSet` VarSet
tmpls)  -- rnEnvL contains the template variables
      = Var -> Maybe Var
forall a. a -> Maybe a
Just (Var -> Var
to_target Var
v')          -- to_target: see (W1)
                                     --   in Note [Matching higher order patterns]
    arg_as_lcl_var CoreExpr
_ = Maybe Var
forall a. Maybe a
Nothing

    can_decompose_app_instead :: Bool
can_decompose_app_instead -- Template (e1 v), target (e2 v), and v # fvs(e2)
      = case (CoreExpr
e1, CoreExpr
e2) of      -- See (W2) in Note [Matching higher order patterns]
           (App CoreExpr
_ (Var Var
v1), App CoreExpr
f2 (Var Var
v2))
             -> RnEnv2 -> Var -> Var
rnOccL RnEnv2
rn_env Var
v1 Var -> Var -> Bool
forall a. Eq a => a -> a -> Bool
== RnEnv2 -> Var -> Var
rnOccR RnEnv2
rn_env Var
v2
                Bool -> Bool -> Bool
&& Bool -> Bool
not (Var
v2 Var -> VarSet -> Bool
`elemVarSet` CoreExpr -> VarSet
exprFreeVars CoreExpr
f2)
           (CoreExpr, CoreExpr)
_ -> Bool
False

    ----------------
    -- to_target: see (W1) in Note [Matching higher order patterns]
    to_target :: Var -> Var   -- From canonical variable back to target-expr variable
    to_target :: Var -> Var
to_target Var
v = VarEnv Var -> Var -> Maybe Var
forall a. VarEnv a -> Var -> Maybe a
lookupVarEnv VarEnv Var
rev_envR Var
v Maybe Var -> Var -> Var
forall a. Maybe a -> a -> a
`orElse` Var
v

    rev_envR :: VarEnv Var   -- Inverts rnEnvR: from canonical variable
                             -- back to target-expr variable
    rev_envR :: VarEnv Var
rev_envR = (Unique -> Var -> VarEnv Var -> VarEnv Var)
-> VarEnv Var -> VarEnv Var -> VarEnv Var
forall a r. (Unique -> a -> r -> r) -> r -> VarEnv a -> r
nonDetStrictFoldVarEnv_Directly Unique -> Var -> VarEnv Var -> VarEnv Var
add_one VarEnv Var
forall a. VarEnv a
emptyVarEnv (RnEnv2 -> VarEnv Var
rnEnvR RnEnv2
rn_env)
    add_one :: Unique -> Var -> VarEnv Var -> VarEnv Var
add_one Unique
uniq Var
var VarEnv Var
env = VarEnv Var -> Var -> Var -> VarEnv Var
forall a. VarEnv a -> Var -> a -> VarEnv a
extendVarEnv VarEnv Var
env Var
var (Var
var Var -> Unique -> Var
`setVarUnique` Unique
uniq)

{- Note [Matching higher order patterns]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Higher order patterns provide a limited form of higher order matching.
See GHC Proposal #555
  https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0555-template-patterns.rst
and #22465 for more details and related work.

Consider the potential match:

   Template: forall f. foo (\x -> f x)
   Target:             foo (\x -> x*2 + x)

The expression `x*2 + x` in the target is not literally an application of a
function to the variable `x`, so the simple application rule does not apply.
However, we can match them modulo beta equivalence with the substitution:

   [f :-> \x -> x*2 + x]

The general problem of higher order matching is tricky to implement, but
the subproblem which we call /higher order pattern matching/ is sufficient
for the given example and much easier to implement.

Design:

We start with terminology.

* /Template variables/. The forall'd variables are called the template
  variables. In the example match above, `f` is a template variable.

* /Local binders/. The local binders of a rule are the variables bound
  inside the template. In the example match above, `x` is a local binder.
  Note that local binders can be term variables and type variables.

A /higher order pattern/ (HOP) is a sub-expression of the template,
of form (f x y z) where:

* (HOP1) f is a template variable
* (HOP2) x, y, z are local binders (like y in rule "wombat" above; see definitions).
* (HOP3) The arguments x, y, z are term variables
* (HOP4) The arguments x, y, z are distinct (no duplicates)

Matching of higher order patterns (HOP-matching). A higher order pattern (f x y z)
(in the template) matches any target expression e provided:

* (HOP5) The target has the same type as the template
* (HOP6) No local binder is free in e, other than x, y, z.

If these two condition hold, the higher order pattern (f x y z) matches
the target expression e, yielding the substitution [f :-> \x y z. e].
Notice that this substitution is type preserving, and the RHS
of the substitution has no free local binders.

HOP matching is small enough to be done in-line in the `match` function.
Two wrinkles:

(W1) Consider the potential match:
        Template:    forall f. foo (\x -> f x)
        Target:                foo (\y -> (y, y))
     During matching we make `x` the canonical variable for the lambdas
     and then we see:
        Template:    f x       rnEnvL = []
        Target:      (y, y)    rnEnvR = [y :-> x]
     We could bind [f :-> \x. (x,x)], by applying rnEnvR substitution to the target
     expression.  But that is tiresome (a) because it involves a traversal, and
     (b) because rnEnvR is a VarEnv Var, and we don't have a substitution function
     for that.

     So instead, we invert rnEnvR, and apply it to the binders, to get
     [f :-> \y. (y,y)].  This is done by `to_target` in the HOP-matching case.
     It takes a little bit of thinking to be sure this will work right in the case
     of shadowing.  E.g.  Template (\x y. f x y)   Target  (\p p. p*p)
     Here rnEnvR will be just [p :-> y], so after inversion we'll get
          [f :-> \x p. p*p]
     but that is fine.

(W2) This wrinkle concerns the overlp between the new HOP rule and the existing
     decompose-application rule.  See 3.1 of GHC Proposal #555 for a discussion.

     Consider potential match:
        Template: forall f.   foo (\x y. Just (f y x))
        Target:               foo (\p q. Just (h (1+q) p)))
     During matching we will encounter:
        Template:    f x y
        Target:      h (1+q) p    rnEnvR = [p:->x, q:->y]
     The rnEnvR renaming `[p:->x, q:->y]` is done by the matcher (today) on the fly,
     to make the bound variables of the template and target "line up".
     But now we can:
     * Either use the new HOP rule to succeed with
          [f :-> \x y. h (1+x) y]
     * Or use the existing decompose-application rule to match
          (f x) against (h (1+q)) and `y` against `p`.
       This will succeed with
          [f :-> \y. h (1+y)]

     Note that the result of the HOP rule will always be eta-equivalent to
     the result of the decompose-application rule.  But the proposal specifies
     that we should use the decompose-application rule because it involves
     less eta-expansion.

     But take care:
        Template: forall f.   foo (\x y. Just (f y x))
        Target:               foo (\p q. Just (h (p+q) p)))
     Then during matching we will encounter:
        Template:    f x y
        Target:      h (p+q) p      rnEnvR = [p:->x, q:->y]
     Now, we cannot use the decompose-application rule, because p is free in
     (h (p+q)). So, we can only use the new HOP rule.

(W3) You might wonder if a HOP can have /type/ arguments, thus (in Core)
        RULE forall h.
             f (\(MkT @b (d::Num b) (x::b)) -> h @b d x) = ...
     where the HOP is (h @b d x). In principle this might be possible, but
     it seems fragile; e.g. we would still need to insist that the (invisible)
     @b was a type variable.  And since `h` gets a polymoprhic type, that
     type would have to be declared by the programmer.

     Maybe one day.  But for now, we insist (in `arg_as_lcl_var`)that a HOP
     has only term-variable arguments.
-}

-- Note the match on MRefl!  We fail if there is a cast in the target
--     (e1 e2) ~ (d1 d2) |> co
-- See Note [Cancel reflexive casts]: in the Cast equations for 'match'
-- we aggressively ensure that if MCo is reflective, it really is MRefl.
match RuleMatchEnv
renv RuleSubst
subst (App CoreExpr
f1 CoreExpr
a1) (App CoreExpr
f2 CoreExpr
a2) MCoercion
MRefl
  = do  { RuleSubst
subst' <- RuleMatchEnv
-> RuleSubst
-> CoreExpr
-> CoreExpr
-> MCoercion
-> Maybe RuleSubst
match RuleMatchEnv
renv RuleSubst
subst CoreExpr
f1 CoreExpr
f2 MCoercion
MRefl
        ; RuleMatchEnv
-> RuleSubst
-> CoreExpr
-> CoreExpr
-> MCoercion
-> Maybe RuleSubst
match RuleMatchEnv
renv RuleSubst
subst' CoreExpr
a1 CoreExpr
a2 MCoercion
MRefl }

------------------------ Float lets ---------------------
match RuleMatchEnv
renv RuleSubst
subst CoreExpr
e1 (Let CoreBind
bind CoreExpr
e2) MCoercion
mco
  | -- pprTrace "match:Let" (vcat [ppr bind, ppr $ okToFloat (rv_lcl renv) (bindFreeVars bind)]) $
    Bool -> Bool
not (CoreBind -> Bool
isJoinBind CoreBind
bind) -- can't float join point out of argument position
  , RnEnv2 -> VarSet -> Bool
okToFloat (RuleMatchEnv -> RnEnv2
rv_lcl RuleMatchEnv
renv) (CoreBind -> VarSet
bindFreeVars CoreBind
bind) -- See Note [Matching lets]
  = RuleMatchEnv
-> RuleSubst
-> CoreExpr
-> CoreExpr
-> MCoercion
-> Maybe RuleSubst
match (RuleMatchEnv
renv { rv_fltR = flt_subst'
                , rv_lcl  = rv_lcl renv `extendRnInScopeSetList` new_bndrs })
                -- We are floating the let-binding out, as if it had enclosed
                -- the entire target from Day 1.  So we must add its binders to
                -- the in-scope set (#20200)
          (RuleSubst
subst { rs_binds = rs_binds subst . Let bind'
                 , rs_bndrs = new_bndrs ++ rs_bndrs subst })
          CoreExpr
e1 CoreExpr
e2 MCoercion
mco
  | Bool
otherwise
  = Maybe RuleSubst
forall a. Maybe a
Nothing
  where
    in_scope :: InScopeSet
in_scope  = RnEnv2 -> InScopeSet
rnInScopeSet (RuleMatchEnv -> RnEnv2
rv_lcl RuleMatchEnv
renv) InScopeSet -> [Var] -> InScopeSet
`extendInScopeSetList` RuleSubst -> [Var]
rs_bndrs RuleSubst
subst
                -- in_scope: see (4) in Note [Matching lets]
    flt_subst :: Subst
flt_subst = RuleMatchEnv -> Subst
rv_fltR RuleMatchEnv
renv Subst -> InScopeSet -> Subst
`setInScope` InScopeSet
in_scope
    (Subst
flt_subst', CoreBind
bind') = (() :: Constraint) => Subst -> CoreBind -> (Subst, CoreBind)
Subst -> CoreBind -> (Subst, CoreBind)
substBind Subst
flt_subst CoreBind
bind
    new_bndrs :: [Var]
new_bndrs           = CoreBind -> [Var]
forall b. Bind b -> [b]
bindersOf CoreBind
bind'

------------------------  Lambdas ---------------------
match RuleMatchEnv
renv RuleSubst
subst (Lam Var
x1 CoreExpr
e1) CoreExpr
e2 MCoercion
mco
  | let casted_e2 :: CoreExpr
casted_e2 = CoreExpr -> MCoercion -> CoreExpr
mkCastMCo CoreExpr
e2 MCoercion
mco
        in_scope :: InScopeSet
in_scope = InScopeSet -> VarSet -> InScopeSet
extendInScopeSetSet (RnEnv2 -> InScopeSet
rnInScopeSet (RuleMatchEnv -> RnEnv2
rv_lcl RuleMatchEnv
renv))
                                       (CoreExpr -> VarSet
exprFreeVars CoreExpr
casted_e2)
        in_scope_env :: InScopeEnv
in_scope_env = InScopeSet -> IdUnfoldingFun -> InScopeEnv
ISE InScopeSet
in_scope (RuleMatchEnv -> IdUnfoldingFun
rv_unf RuleMatchEnv
renv)
        -- extendInScopeSetSet: The InScopeSet of rn_env is not necessarily
        -- a superset of the free vars of e2; it is only guaranteed a superset of
        -- applyng the (rnEnvR rn_env) substitution to e2. But exprIsLambda_maybe
        -- wants an in-scope set that includes all the free vars of its argument.
        -- Hence adding adding (exprFreeVars casted_e2) to the in-scope set (#23630)
  , Just (Var
x2, CoreExpr
e2', [CoreTickish]
ts) <- (() :: Constraint) =>
InScopeEnv -> CoreExpr -> Maybe (Var, CoreExpr, [CoreTickish])
InScopeEnv -> CoreExpr -> Maybe (Var, CoreExpr, [CoreTickish])
exprIsLambda_maybe InScopeEnv
in_scope_env CoreExpr
casted_e2
    -- See Note [Lambdas in the template]
  = let renv' :: RuleMatchEnv
renv'  = RuleMatchEnv -> Var -> Var -> RuleMatchEnv
rnMatchBndr2 RuleMatchEnv
renv Var
x1 Var
x2
        subst' :: RuleSubst
subst' = RuleSubst
subst { rs_binds = rs_binds subst . flip (foldr mkTick) ts }
    in  RuleMatchEnv
-> RuleSubst
-> CoreExpr
-> CoreExpr
-> MCoercion
-> Maybe RuleSubst
match RuleMatchEnv
renv' RuleSubst
subst' CoreExpr
e1 CoreExpr
e2' MCoercion
MRefl

match RuleMatchEnv
renv RuleSubst
subst CoreExpr
e1 e2 :: CoreExpr
e2@(Lam {}) MCoercion
mco
  | Just (RuleMatchEnv
renv', CoreExpr
e2') <- RuleMatchEnv -> CoreExpr -> Maybe (RuleMatchEnv, CoreExpr)
eta_reduce RuleMatchEnv
renv CoreExpr
e2  -- See Note [Eta reduction in the target]
  = RuleMatchEnv
-> RuleSubst
-> CoreExpr
-> CoreExpr
-> MCoercion
-> Maybe RuleSubst
match RuleMatchEnv
renv' RuleSubst
subst CoreExpr
e1 CoreExpr
e2' MCoercion
mco

{- Note [Lambdas in the template]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If we match
   Template:   (\x. blah_template)
   Target:     (\y. blah_target)
then we want to match inside the lambdas, using rv_lcl to match up
x and y.

But what about this?
   Template   (\x. (blah1 |> cv))
   Target     (\y. blah2) |> co

This happens quite readily, because the Simplifier generally moves
casts outside lambdas: see Note [Casts and lambdas] in
GHC.Core.Opt.Simplify.Utils. So, tiresomely, we want to push `co`
back inside, which is what `exprIsLambda_maybe` does.  But we've
stripped off that cast, so now we need to put it back, hence mkCastMCo.

Unlike the target, where we attempt eta-reduction, we do not attempt
to eta-reduce the template, and may therefore fail on
  Template:   \x. f True x
  Target      f True

It's not especially easy to deal with eta reducing the template,
and never happens, because no one write eta-expanded left-hand-sides.
-}

------------------------ Case expression ---------------------
{- Disabled: see Note [Matching cases] below
match renv (tv_subst, id_subst, binds) e1
      (Case scrut case_bndr ty [(con, alt_bndrs, rhs)])
  | exprOkForSpeculation scrut  -- See Note [Matching cases]
  , okToFloat rn_env bndrs (exprFreeVars scrut)
  = match (renv { me_env = rn_env' })
          (tv_subst, id_subst, binds . case_wrap)
          e1 rhs
  where
    rn_env   = me_env renv
    rn_env'  = extendRnInScopeList rn_env bndrs
    bndrs    = case_bndr : alt_bndrs
    case_wrap rhs' = Case scrut case_bndr ty [(con, alt_bndrs, rhs')]
-}

match RuleMatchEnv
renv RuleSubst
subst (Case CoreExpr
e1 Var
x1 Kind
ty1 [Alt Var]
alts1) (Case CoreExpr
e2 Var
x2 Kind
ty2 [Alt Var]
alts2) MCoercion
mco
  = do  { RuleSubst
subst1 <- RuleMatchEnv -> RuleSubst -> Kind -> Kind -> Maybe RuleSubst
match_ty RuleMatchEnv
renv RuleSubst
subst Kind
ty1 Kind
ty2
        ; RuleSubst
subst2 <- RuleMatchEnv
-> RuleSubst
-> CoreExpr
-> CoreExpr
-> MCoercion
-> Maybe RuleSubst
match RuleMatchEnv
renv RuleSubst
subst1 CoreExpr
e1 CoreExpr
e2 MCoercion
MRefl
        ; let renv' :: RuleMatchEnv
renv' = RuleMatchEnv -> Var -> Var -> RuleMatchEnv
rnMatchBndr2 RuleMatchEnv
renv Var
x1 Var
x2
        ; RuleMatchEnv
-> RuleSubst
-> [Alt Var]
-> [Alt Var]
-> MCoercion
-> Maybe RuleSubst
match_alts RuleMatchEnv
renv' RuleSubst
subst2 [Alt Var]
alts1 [Alt Var]
alts2 MCoercion
mco   -- Alts are both sorted
        }

-- Everything else fails
match RuleMatchEnv
_ RuleSubst
_ CoreExpr
_e1 CoreExpr
_e2 MCoercion
_mco = -- pprTrace "Failing at" ((text "e1:" <+> ppr _e1) $$ (text "e2:" <+> ppr _e2)) $
                         Maybe RuleSubst
forall a. Maybe a
Nothing

-------------
eta_reduce :: RuleMatchEnv -> CoreExpr -> Maybe (RuleMatchEnv, CoreExpr)
-- See Note [Eta reduction in the target]
eta_reduce :: RuleMatchEnv -> CoreExpr -> Maybe (RuleMatchEnv, CoreExpr)
eta_reduce RuleMatchEnv
renv e :: CoreExpr
e@(Lam {})
  = RuleMatchEnv
-> (CoreExpr -> CoreExpr)
-> [Var]
-> CoreExpr
-> Maybe (RuleMatchEnv, CoreExpr)
go RuleMatchEnv
renv CoreExpr -> CoreExpr
forall a. a -> a
id [] CoreExpr
e
  where
    go :: RuleMatchEnv -> BindWrapper -> [Var] -> CoreExpr
       -> Maybe (RuleMatchEnv, CoreExpr)
    go :: RuleMatchEnv
-> (CoreExpr -> CoreExpr)
-> [Var]
-> CoreExpr
-> Maybe (RuleMatchEnv, CoreExpr)
go RuleMatchEnv
renv CoreExpr -> CoreExpr
bw [Var]
vs (Let CoreBind
b CoreExpr
e) = RuleMatchEnv
-> (CoreExpr -> CoreExpr)
-> [Var]
-> CoreExpr
-> Maybe (RuleMatchEnv, CoreExpr)
go RuleMatchEnv
renv (CoreExpr -> CoreExpr
bw (CoreExpr -> CoreExpr)
-> (CoreExpr -> CoreExpr) -> CoreExpr -> CoreExpr
forall b c a. (b -> c) -> (a -> b) -> a -> c
. CoreBind -> CoreExpr -> CoreExpr
forall b. Bind b -> Expr b -> Expr b
Let CoreBind
b) [Var]
vs CoreExpr
e

    go RuleMatchEnv
renv CoreExpr -> CoreExpr
bw [Var]
vs (Lam Var
v CoreExpr
e) = RuleMatchEnv
-> (CoreExpr -> CoreExpr)
-> [Var]
-> CoreExpr
-> Maybe (RuleMatchEnv, CoreExpr)
go RuleMatchEnv
renv' CoreExpr -> CoreExpr
bw (Var
v'Var -> [Var] -> [Var]
forall a. a -> [a] -> [a]
:[Var]
vs) CoreExpr
e
      where
         (RnEnv2
rn_env', Var
v') = RnEnv2 -> Var -> (RnEnv2, Var)
rnBndrR (RuleMatchEnv -> RnEnv2
rv_lcl RuleMatchEnv
renv) Var
v
         renv' :: RuleMatchEnv
renv' = RuleMatchEnv
renv { rv_lcl = rn_env' }

    go RuleMatchEnv
renv CoreExpr -> CoreExpr
bw (Var
v:[Var]
vs) (App CoreExpr
f CoreExpr
arg)
      | Var Var
a <- CoreExpr
arg, Var
v Var -> Var -> Bool
forall a. Eq a => a -> a -> Bool
== RnEnv2 -> Var -> Var
rnOccR (RuleMatchEnv -> RnEnv2
rv_lcl RuleMatchEnv
renv) Var
a
      = RuleMatchEnv
-> (CoreExpr -> CoreExpr)
-> [Var]
-> CoreExpr
-> Maybe (RuleMatchEnv, CoreExpr)
go RuleMatchEnv
renv CoreExpr -> CoreExpr
bw [Var]
vs CoreExpr
f

      | Type Kind
ty <- CoreExpr
arg, Just Var
tv <- Kind -> Maybe Var
getTyVar_maybe Kind
ty
      , Var
v Var -> Var -> Bool
forall a. Eq a => a -> a -> Bool
== RnEnv2 -> Var -> Var
rnOccR (RuleMatchEnv -> RnEnv2
rv_lcl RuleMatchEnv
renv) Var
tv
      = RuleMatchEnv
-> (CoreExpr -> CoreExpr)
-> [Var]
-> CoreExpr
-> Maybe (RuleMatchEnv, CoreExpr)
go RuleMatchEnv
renv CoreExpr -> CoreExpr
bw [Var]
vs CoreExpr
f

    go RuleMatchEnv
renv CoreExpr -> CoreExpr
bw []    CoreExpr
e = (RuleMatchEnv, CoreExpr) -> Maybe (RuleMatchEnv, CoreExpr)
forall a. a -> Maybe a
Just (RuleMatchEnv
renv, CoreExpr -> CoreExpr
bw CoreExpr
e)
    go RuleMatchEnv
_    CoreExpr -> CoreExpr
_  (Var
_:[Var]
_) CoreExpr
_ = Maybe (RuleMatchEnv, CoreExpr)
forall a. Maybe a
Nothing

eta_reduce RuleMatchEnv
_ CoreExpr
_ = Maybe (RuleMatchEnv, CoreExpr)
forall a. Maybe a
Nothing

{- Note [Eta reduction in the target]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suppose we are faced with this (#19790)
   Template {x}  f x
   Target        (\a b c. let blah in f x a b c)

You might wonder why we have an eta-expanded target (see first subtle
point below), but regardless of how it came about, we'd like
eta-expansion not to impede matching.

So eta_reduce does on-the-fly eta-reduction of the target expression.
Given (\a b c. let blah in e a b c), it returns (let blah in e).

Subtle points:
* Consider a target:  \x. f <expensive> x
  In the main eta-reducer we do not eta-reduce this, because doing so
  might reduce the arity of the expression (from 1 to zero, because of
  <expensive>).  But for rule-matching we /do/ want to match template
  (f a) against target (\x. f <expensive> x), with a := <expensive>

  This is a compelling reason for not relying on the Simplifier's
  eta-reducer.

* The Lam case of eta_reduce renames as it goes. Consider
  (\x. \x. f x x).  We should not eta-reduce this.  As we go we rename
  the first x to x1, and the second to x2; then both argument x's are x2.

* eta_reduce does /not/ need to check that the bindings 'blah'
  and expression 'e' don't mention a b c; but it /does/ extend the
  rv_lcl RnEnv2 (see rn_bndr in eta_reduce).
  * If 'blah' mentions the binders, the let-float rule won't
    fire; and
  * if 'e' mentions the binders we we'll also fail to match
    e.g. because of the exprFreeVars test in match_tmpl_var.

  Example: Template: {x}  f a         -- Some top-level 'a'
           Target:   (\a b. f a a b)  -- The \a shadows top level 'a'
  Then eta_reduce will /succeed/, with
      (rnEnvR = [a :-> a'], f a)
  The returned RnEnv will map [a :-> a'], where a' is fresh. (There is
  no need to rename 'b' because (in this example) it is not in scope.
  So it's as if we'd returned (f a') from eta_reduce; the renaming applied
  to the target is simply deferred.

Note [Cancel reflexive casts]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Here is an example (from #19790) which we want to catch
   (f x) ~ (\a b. (f x |> co) a b) |> sym co
where
   f :: Int -> Stream
   co :: Stream ~ T1 -> T2 -> T3

when we eta-reduce (\a b. blah a b) to 'blah', we'll get
  (f x) ~ (f x) |> co |> sym co

and we really want to spot that the co/sym-co cancels out.
Hence
  * We keep an invariant that the MCoercion is always MRefl
    if the MCoercion is reflexive
  * We maintain this invariant via the call to checkReflexiveMCo
    in the Cast case of 'match'.
-}

-------------
match_co :: RuleMatchEnv
         -> RuleSubst
         -> Coercion
         -> Coercion
         -> Maybe RuleSubst
-- We only match if the template is a coercion variable or Refl:
--   see Note [Casts in the template]
-- Like 'match' it is /not/ guaranteed that
--     coercionKind template  =  coercionKind target
-- But if match_co succeeds, it /is/ guaranteed that
--     coercionKind (subst template) = coercionKind target

match_co :: RuleMatchEnv
-> RuleSubst -> Coercion -> Coercion -> Maybe RuleSubst
match_co RuleMatchEnv
renv RuleSubst
subst Coercion
co1 Coercion
co2
  | Just Var
cv <- Coercion -> Maybe Var
getCoVar_maybe Coercion
co1
  = RuleMatchEnv -> RuleSubst -> Var -> CoreExpr -> Maybe RuleSubst
match_var RuleMatchEnv
renv RuleSubst
subst Var
cv (Coercion -> CoreExpr
forall b. Coercion -> Expr b
Coercion Coercion
co2)

  | Just (Kind
ty1, Role
r1) <- Coercion -> Maybe (Kind, Role)
isReflCo_maybe Coercion
co1
  = do { (Kind
ty2, Role
r2) <- Coercion -> Maybe (Kind, Role)
isReflCo_maybe Coercion
co2
       ; Bool -> Maybe ()
forall (f :: * -> *). Alternative f => Bool -> f ()
guard (Role
r1 Role -> Role -> Bool
forall a. Eq a => a -> a -> Bool
== Role
r2)
       ; RuleMatchEnv -> RuleSubst -> Kind -> Kind -> Maybe RuleSubst
match_ty RuleMatchEnv
renv RuleSubst
subst Kind
ty1 Kind
ty2 }

  | Bool
debugIsOn
  = String -> SDoc -> Maybe RuleSubst -> Maybe RuleSubst
forall a. String -> SDoc -> a -> a
pprTrace String
"match_co: needs more cases" (Coercion -> SDoc
forall a. Outputable a => a -> SDoc
ppr Coercion
co1 SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ Coercion -> SDoc
forall a. Outputable a => a -> SDoc
ppr Coercion
co2) Maybe RuleSubst
forall a. Maybe a
Nothing
    -- Currently just deals with CoVarCo and Refl

  | Bool
otherwise
  = Maybe RuleSubst
forall a. Maybe a
Nothing

-------------
rnMatchBndr2 :: RuleMatchEnv -> Var -> Var -> RuleMatchEnv
rnMatchBndr2 :: RuleMatchEnv -> Var -> Var -> RuleMatchEnv
rnMatchBndr2 RuleMatchEnv
renv Var
x1 Var
x2
  = RuleMatchEnv
renv { rv_lcl  = rnBndr2 (rv_lcl renv) x1 x2
         , rv_fltR = delBndr (rv_fltR renv) x2 }


------------------------------------------
match_alts :: RuleMatchEnv
           -> RuleSubst
           -> [CoreAlt]                 -- Template
           -> [CoreAlt] -> MCoercion    -- Target
           -> Maybe RuleSubst
match_alts :: RuleMatchEnv
-> RuleSubst
-> [Alt Var]
-> [Alt Var]
-> MCoercion
-> Maybe RuleSubst
match_alts RuleMatchEnv
_ RuleSubst
subst [] [] MCoercion
_
  = RuleSubst -> Maybe RuleSubst
forall a. a -> Maybe a
forall (m :: * -> *) a. Monad m => a -> m a
return RuleSubst
subst
match_alts RuleMatchEnv
renv RuleSubst
subst (Alt AltCon
c1 [Var]
vs1 CoreExpr
r1:[Alt Var]
alts1) (Alt AltCon
c2 [Var]
vs2 CoreExpr
r2:[Alt Var]
alts2) MCoercion
mco
  | AltCon
c1 AltCon -> AltCon -> Bool
forall a. Eq a => a -> a -> Bool
== AltCon
c2
  = do  { RuleSubst
subst1 <- RuleMatchEnv
-> RuleSubst
-> CoreExpr
-> CoreExpr
-> MCoercion
-> Maybe RuleSubst
match RuleMatchEnv
renv' RuleSubst
subst CoreExpr
r1 CoreExpr
r2 MCoercion
mco
        ; RuleMatchEnv
-> RuleSubst
-> [Alt Var]
-> [Alt Var]
-> MCoercion
-> Maybe RuleSubst
match_alts RuleMatchEnv
renv RuleSubst
subst1 [Alt Var]
alts1 [Alt Var]
alts2 MCoercion
mco }
  where
    renv' :: RuleMatchEnv
renv' = (RuleMatchEnv -> (Var, Var) -> RuleMatchEnv)
-> RuleMatchEnv -> [(Var, Var)] -> RuleMatchEnv
forall b a. (b -> a -> b) -> b -> [a] -> b
forall (t :: * -> *) b a.
Foldable t =>
(b -> a -> b) -> b -> t a -> b
foldl' RuleMatchEnv -> (Var, Var) -> RuleMatchEnv
mb RuleMatchEnv
renv ([Var]
vs1 [Var] -> [Var] -> [(Var, Var)]
forall a b. [a] -> [b] -> [(a, b)]
`zip` [Var]
vs2)
    mb :: RuleMatchEnv -> (Var, Var) -> RuleMatchEnv
mb RuleMatchEnv
renv (Var
v1,Var
v2) = RuleMatchEnv -> Var -> Var -> RuleMatchEnv
rnMatchBndr2 RuleMatchEnv
renv Var
v1 Var
v2

match_alts RuleMatchEnv
_ RuleSubst
_ [Alt Var]
_ [Alt Var]
_ MCoercion
_
  = Maybe RuleSubst
forall a. Maybe a
Nothing

------------------------------------------
okToFloat :: RnEnv2 -> VarSet -> Bool
okToFloat :: RnEnv2 -> VarSet -> Bool
okToFloat RnEnv2
rn_env VarSet
bind_fvs
  = (Var -> Bool) -> VarSet -> Bool
allVarSet Var -> Bool
not_captured VarSet
bind_fvs
  where
    not_captured :: Var -> Bool
not_captured Var
fv = Bool -> Bool
not (RnEnv2 -> Var -> Bool
inRnEnvR RnEnv2
rn_env Var
fv)

------------------------------------------
match_var :: RuleMatchEnv
          -> RuleSubst
          -> Var        -- Template
          -> CoreExpr   -- Target
          -> Maybe RuleSubst
match_var :: RuleMatchEnv -> RuleSubst -> Var -> CoreExpr -> Maybe RuleSubst
match_var renv :: RuleMatchEnv
renv@(RV { rv_tmpls :: RuleMatchEnv -> VarSet
rv_tmpls = VarSet
tmpls, rv_lcl :: RuleMatchEnv -> RnEnv2
rv_lcl = RnEnv2
rn_env, rv_fltR :: RuleMatchEnv -> Subst
rv_fltR = Subst
flt_env })
          RuleSubst
subst Var
v1 CoreExpr
e2
  | Var
v1' Var -> VarSet -> Bool
`elemVarSet` VarSet
tmpls
  = RuleMatchEnv -> RuleSubst -> Var -> CoreExpr -> Maybe RuleSubst
match_tmpl_var RuleMatchEnv
renv RuleSubst
subst Var
v1' CoreExpr
e2

  | Bool
otherwise   -- v1' is not a template variable; check for an exact match with e2
  = case CoreExpr
e2 of  -- Remember, envR of rn_env is disjoint from rv_fltR
       Var Var
v2 | Just Var
v2' <- RnEnv2 -> Var -> Maybe Var
rnOccR_maybe RnEnv2
rn_env Var
v2
              -> -- v2 was bound by a nested lambda or case
                 if Var
v1' Var -> Var -> Bool
forall a. Eq a => a -> a -> Bool
== Var
v2' then RuleSubst -> Maybe RuleSubst
forall a. a -> Maybe a
Just RuleSubst
subst
                               else Maybe RuleSubst
forall a. Maybe a
Nothing

              -- v2 is not bound nestedly; it is free
              -- in the whole expression being matched
              -- So it will be in the InScopeSet for flt_env (#20200)
              | Var Var
v2' <- (() :: Constraint) => Subst -> Var -> CoreExpr
Subst -> Var -> CoreExpr
lookupIdSubst Subst
flt_env Var
v2
              , Var
v1' Var -> Var -> Bool
forall a. Eq a => a -> a -> Bool
== Var
v2'
              -> RuleSubst -> Maybe RuleSubst
forall a. a -> Maybe a
Just RuleSubst
subst
              | Bool
otherwise
              -> Maybe RuleSubst
forall a. Maybe a
Nothing

       CoreExpr
_ -> Maybe RuleSubst
forall a. Maybe a
Nothing

  where
    v1' :: Var
v1' = RnEnv2 -> Var -> Var
rnOccL RnEnv2
rn_env Var
v1
        -- If the template is
        --      forall x. f x (\x -> x) = ...
        -- Then the x inside the lambda isn't the
        -- template x, so we must rename first!

------------------------------------------
match_tmpl_var :: RuleMatchEnv
               -> RuleSubst
               -> Var                -- Template
               -> CoreExpr           -- Target
               -> Maybe RuleSubst

match_tmpl_var :: RuleMatchEnv -> RuleSubst -> Var -> CoreExpr -> Maybe RuleSubst
match_tmpl_var renv :: RuleMatchEnv
renv@(RV { rv_lcl :: RuleMatchEnv -> RnEnv2
rv_lcl = RnEnv2
rn_env, rv_fltR :: RuleMatchEnv -> Subst
rv_fltR = Subst
flt_env })
               subst :: RuleSubst
subst@(RS { rs_id_subst :: RuleSubst -> IdSubstEnv
rs_id_subst = IdSubstEnv
id_subst, rs_bndrs :: RuleSubst -> [Var]
rs_bndrs = [Var]
let_bndrs })
               Var
v1' CoreExpr
e2
  -- anyInRnEnvR is lazy in the 2nd arg which allows us to avoid computing fvs
  -- if the right side of the env is empty.
  | RnEnv2 -> VarSet -> Bool
anyInRnEnvR RnEnv2
rn_env (CoreExpr -> VarSet
exprFreeVars CoreExpr
e2)
  = Maybe RuleSubst
forall a. Maybe a
Nothing     -- Skolem-escape failure
                -- e.g. match forall a. (\x -> a) against (\y -> y)

  | Just CoreExpr
e1' <- IdSubstEnv -> Var -> Maybe CoreExpr
forall a. VarEnv a -> Var -> Maybe a
lookupVarEnv IdSubstEnv
id_subst Var
v1'
  = if CoreExpr -> CoreExpr -> Bool
eqCoreExpr CoreExpr
e1' CoreExpr
e2'
    then RuleSubst -> Maybe RuleSubst
forall a. a -> Maybe a
Just RuleSubst
subst
    else Maybe RuleSubst
forall a. Maybe a
Nothing

  | Bool
otherwise   -- See Note [Matching variable types]
  = do { RuleSubst
subst' <- RuleMatchEnv -> RuleSubst -> Kind -> Kind -> Maybe RuleSubst
match_ty RuleMatchEnv
renv RuleSubst
subst (Var -> Kind
idType Var
v1') ((() :: Constraint) => CoreExpr -> Kind
CoreExpr -> Kind
exprType CoreExpr
e2)
       ; RuleSubst -> Maybe RuleSubst
forall a. a -> Maybe a
forall (m :: * -> *) a. Monad m => a -> m a
return (RuleSubst
subst' { rs_id_subst = id_subst' }) }
  where
    -- e2' is the result of applying flt_env to e2
    e2' :: CoreExpr
e2' | [Var] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [Var]
let_bndrs = CoreExpr
e2
        | Bool
otherwise = (() :: Constraint) => Subst -> CoreExpr -> CoreExpr
Subst -> CoreExpr -> CoreExpr
substExpr Subst
flt_env CoreExpr
e2

    id_subst' :: IdSubstEnv
id_subst' = IdSubstEnv -> Var -> CoreExpr -> IdSubstEnv
forall a. VarEnv a -> Var -> a -> VarEnv a
extendVarEnv (RuleSubst -> IdSubstEnv
rs_id_subst RuleSubst
subst) Var
v1' CoreExpr
e2'
         -- No further renaming to do on e2',
         -- because no free var of e2' is in the rnEnvR of the envt

------------------------------------------

match_ty :: RuleMatchEnv
         -> RuleSubst
         -> Type                -- Template
         -> Type                -- Target
         -> Maybe RuleSubst
-- Matching Core types: use the matcher in GHC.Tc.Utils.TcType.
-- Notice that we treat newtypes as opaque.  For example, suppose
-- we have a specialised version of a function at a newtype, say
--      newtype T = MkT Int
-- We only want to replace (f T) with f', not (f Int).

match_ty :: RuleMatchEnv -> RuleSubst -> Kind -> Kind -> Maybe RuleSubst
match_ty (RV { rv_tmpls :: RuleMatchEnv -> VarSet
rv_tmpls = VarSet
tmpls, rv_lcl :: RuleMatchEnv -> RnEnv2
rv_lcl = RnEnv2
rn_env })
         subst :: RuleSubst
subst@(RS { rs_tv_subst :: RuleSubst -> TvSubstEnv
rs_tv_subst = TvSubstEnv
tv_subst })
         Kind
ty1 Kind
ty2
  = do  { TvSubstEnv
tv_subst' <- VarSet -> RnEnv2 -> TvSubstEnv -> Kind -> Kind -> Maybe TvSubstEnv
Unify.ruleMatchTyKiX VarSet
tmpls RnEnv2
rn_env TvSubstEnv
tv_subst Kind
ty1 Kind
ty2
               -- NB: ruleMatchTyKiX applis tv_subst to ty1 only
               --     and of course only binds 'tmpls'
        ; RuleSubst -> Maybe RuleSubst
forall a. a -> Maybe a
forall (m :: * -> *) a. Monad m => a -> m a
return (RuleSubst
subst { rs_tv_subst = tv_subst' }) }

{- Note [Matching variable types]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When matching x ~ e, where 'x' is a template variable, we must check that
x's type matches e's type, to establish (TypeInv).  For example
  forall (c::Char->Int) (x::Char).
     f (c x) = "RULE FIRED"
We must not match on, say (f (pred (3::Int))).

It's actually quite difficult to come up with an example that shows
you need type matching, esp since matching is left-to-right, so type
args get matched first.  But it's possible (e.g. simplrun008) and this
is the Right Thing to do.

An alternative would be to make (TypeInf) into a /pre-condition/.  It
is threatened only by the App rule.  So when matching an application
(e1 e2) ~ (d1 d2) would be to collect args of the application chain,
match the types of the head, then match arg-by-arg.

However that alternative seems a bit more complicated.  And by
matching types at variables we do one match_ty for each template
variable, rather than one for each application chain.  Usually there are
fewer template variables, although for simple rules it could be the other
way around.

Note [Expanding variables]
~~~~~~~~~~~~~~~~~~~~~~~~~~
Here is another Very Important rule: if the term being matched is a
variable, we expand it so long as its unfolding is "expandable". (Its
occurrence information is not necessarily up to date, so we don't use
it.)  By "expandable" we mean a WHNF or a "constructor-like" application.
This is the key reason for "constructor-like" Ids.  If we have
     {-# NOINLINE [1] CONLIKE g #-}
     {-# RULE f (g x) = h x #-}
then in the term
   let v = g 3 in ....(f v)....
we want to make the rule fire, to replace (f v) with (h 3).

Note [Do not expand locally-bound variables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Do *not* expand locally-bound variables, else there's a worry that the
unfolding might mention variables that are themselves renamed.
Example
          case x of y { (p,q) -> ...y... }
Don't expand 'y' to (p,q) because p,q might themselves have been
renamed.  Essentially we only expand unfoldings that are "outside"
the entire match.

Hence, (a) the guard (not (isLocallyBoundR v2))
       (b) when we expand we nuke the renaming envt (nukeRnEnvR).

Note [Tick annotations in RULE matching]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We used to unconditionally look through ticks in both template and
expression being matched. This is actually illegal for counting or
cost-centre-scoped ticks, because we have no place to put them without
changing entry counts and/or costs. So now we just fail the match in
these cases.

On the other hand, where we are allowed to insert new cost into the
tick scope, we can float them upwards to the rule application site.

Moreover, we may encounter ticks in the template of a rule. There are a few
ways in which these may be introduced (e.g. #18162, #17619). Such ticks are
ignored by the matcher. See Note [Simplifying rules] in
GHC.Core.Opt.Simplify.Utils for details.

cf Note [Tick annotations in call patterns] in GHC.Core.Opt.SpecConstr


Note [Matching lets]
~~~~~~~~~~~~~~~~~~~~
Matching a let-expression.  Consider
        RULE forall x.  f (g x) = <rhs>
and target expression
        f (let { w=R } in g E))
Then we'd like the rule to match, to generate
        let { w=R } in (\x. <rhs>) E
In effect, we want to float the let-binding outward, to enable
the match to happen.  This is the WHOLE REASON for accumulating
bindings in the RuleSubst

We can only do this if the free variables of R are not bound by the
part of the target expression outside the let binding; e.g.
        f (\v. let w = v+1 in g E)
Here we obviously cannot float the let-binding for w.  Hence the
use of okToFloat.

There are a couple of tricky points:
  (a) What if floating the binding captures a variable that is
      free in the entire expression?
        f (let v = x+1 in v) v
      --> NOT!
        let v = x+1 in f (x+1) v

  (b) What if the let shadows a local binding?
        f (\v -> (v, let v = x+1 in (v,v))
      --> NOT!
        let v = x+1 in f (\v -> (v, (v,v)))

  (c) What if two non-nested let bindings bind the same variable?
        f (let v = e1 in b1) (let v = e2 in b2)
      --> NOT!
        let v = e1 in let v = e2 in (f b2 b2)
      See testsuite test `T4814`.

Our cunning plan is this:
  (1) Along with the growing substitution for template variables
      we maintain a growing set of floated let-bindings (rs_binds)
      plus the set of variables thus bound (rs_bndrs).

  (2) The RnEnv2 in the MatchEnv binds only the local binders
      in the term (lambdas, case), not the floated let-bndrs.

  (3) When we encounter a `let` in the term to be matched, in the Let
      case of `match`, we use `okToFloat` to check that it does not mention any
      locally bound (lambda, case) variables.  If so we fail.

  (4) In the Let case of `match`, we use GHC.Core.Subst.substBind to
      freshen the binding (which, remember (3), mentions no locally
      bound variables), in a lexically-scoped way (via rv_fltR in
      MatchEnv).

      The subtle point is that we want an in-scope set for this
      substitution that includes /two/ sets:
      * The in-scope variables at this point, so that we avoid using
        those local names for the floated binding; points (a) and (b) above.
      * All "earlier" floated bindings, so that we avoid using the
        same name for two different floated bindings; point (c) above.

      Because we have to compute the in-scope set here, the in-scope set
      stored in `rv_fltR` is always ignored; we leave it only because it's
      convenient to have `rv_fltR :: Subst` (with an always-ignored `InScopeSet`)
      rather than storing three separate substitutions.

  (5) We apply that freshening substitution, in a lexically-scoped
      way to the term, although lazily; this is the rv_fltR field.

See #4814, which is an issue resulting from getting this wrong.

Note [Matching cases]
~~~~~~~~~~~~~~~~~~~~~
{- NOTE: This idea is currently disabled.  It really only works if
         the primops involved are OkForSpeculation, and, since
         they have side effects readIntOfAddr and touch are not.
         Maybe we'll get back to this later .  -}

Consider
   f (case readIntOffAddr# p# i# realWorld# of { (# s#, n# #) ->
      case touch# fp s# of { _ ->
      I# n# } } )
This happened in a tight loop generated by stream fusion that
Roman encountered.  We'd like to treat this just like the let
case, because the primops concerned are ok-for-speculation.
That is, we'd like to behave as if it had been
   case readIntOffAddr# p# i# realWorld# of { (# s#, n# #) ->
   case touch# fp s# of { _ ->
   f (I# n# } } )

Note [Lookup in-scope]
~~~~~~~~~~~~~~~~~~~~~~
Consider this example
        foo :: Int -> Maybe Int -> Int
        foo 0 (Just n) = n
        foo m (Just n) = foo (m-n) (Just n)

SpecConstr sees this fragment:

        case w_smT of wild_Xf [Just A] {
          Data.Maybe.Nothing -> lvl_smf;
          Data.Maybe.Just n_acT [Just S(L)] ->
            case n_acT of wild1_ams [Just A] { GHC.Base.I# y_amr [Just L] ->
              $wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
            }};

and correctly generates the rule

        RULES: "SC:$wfoo1" [0] __forall {y_amr [Just L] :: GHC.Prim.Int#
                                          sc_snn :: GHC.Prim.Int#}
          $wfoo_smW sc_snn (Data.Maybe.Just @ GHC.Base.Int (GHC.Base.I# y_amr))
          = $s$wfoo_sno y_amr sc_snn ;]

BUT we must ensure that this rule matches in the original function!
Note that the call to $wfoo is
            $wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf

During matching we expand wild_Xf to (Just n_acT).  But then we must also
expand n_acT to (I# y_amr).  And we can only do that if we look up n_acT
in the in-scope set, because in wild_Xf's unfolding it won't have an unfolding
at all.

That is why the 'lookupRnInScope' call in the (Var v2) case of 'match'
is so important.


************************************************************************
*                                                                      *
                   Rule-check the program
*                                                                      *
************************************************************************

   We want to know what sites have rules that could have fired but didn't.
   This pass runs over the tree (without changing it) and reports such.
-}

-- | Report partial matches for rules beginning with the specified
-- string for the purposes of error reporting
ruleCheckProgram :: RuleOpts                    -- ^ Rule options
                 -> CompilerPhase               -- ^ Rule activation test
                 -> String                      -- ^ Rule pattern
                 -> (Id -> [CoreRule])          -- ^ Rules for an Id
                 -> CoreProgram                 -- ^ Bindings to check in
                 -> SDoc                        -- ^ Resulting check message
ruleCheckProgram :: RuleOpts
-> CompilerPhase
-> String
-> (Var -> [CoreRule])
-> [CoreBind]
-> SDoc
ruleCheckProgram RuleOpts
ropts CompilerPhase
phase String
rule_pat Var -> [CoreRule]
rules [CoreBind]
binds
  | Bag SDoc -> Bool
forall a. Bag a -> Bool
isEmptyBag Bag SDoc
results
  = String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Rule check results: no rule application sites"
  | Bool
otherwise
  = [SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat [String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Rule check results:",
          SDoc
line,
          [SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat [ SDoc
p SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ SDoc
line | SDoc
p <- Bag SDoc -> [SDoc]
forall a. Bag a -> [a]
bagToList Bag SDoc
results ]
         ]
  where
    env :: RuleCheckEnv
env = RuleCheckEnv { rc_is_active :: Activation -> Bool
rc_is_active = CompilerPhase -> Activation -> Bool
isActive CompilerPhase
phase
                       , rc_id_unf :: IdUnfoldingFun
rc_id_unf    = IdUnfoldingFun
idUnfolding     -- Not quite right
                                                        -- Should use activeUnfolding
                       , rc_pattern :: String
rc_pattern   = String
rule_pat
                       , rc_rules :: Var -> [CoreRule]
rc_rules     = Var -> [CoreRule]
rules
                       , rc_ropts :: RuleOpts
rc_ropts     = RuleOpts
ropts
                       }
    results :: Bag SDoc
results = [Bag SDoc] -> Bag SDoc
forall a. [Bag a] -> Bag a
unionManyBags ((CoreBind -> Bag SDoc) -> [CoreBind] -> [Bag SDoc]
forall a b. (a -> b) -> [a] -> [b]
map (RuleCheckEnv -> CoreBind -> Bag SDoc
ruleCheckBind RuleCheckEnv
env) [CoreBind]
binds)
    line :: SDoc
line = String -> SDoc
forall doc. IsLine doc => String -> doc
text (Arity -> Char -> String
forall a. Arity -> a -> [a]
replicate Arity
20 Char
'-')

data RuleCheckEnv = RuleCheckEnv {
    RuleCheckEnv -> Activation -> Bool
rc_is_active :: Activation -> Bool,
    RuleCheckEnv -> IdUnfoldingFun
rc_id_unf  :: IdUnfoldingFun,
    RuleCheckEnv -> String
rc_pattern :: String,
    RuleCheckEnv -> Var -> [CoreRule]
rc_rules :: Id -> [CoreRule],
    RuleCheckEnv -> RuleOpts
rc_ropts :: RuleOpts
}

ruleCheckBind :: RuleCheckEnv -> CoreBind -> Bag SDoc
   -- The Bag returned has one SDoc for each call site found
ruleCheckBind :: RuleCheckEnv -> CoreBind -> Bag SDoc
ruleCheckBind RuleCheckEnv
env (NonRec Var
_ CoreExpr
r) = RuleCheckEnv -> CoreExpr -> Bag SDoc
ruleCheck RuleCheckEnv
env CoreExpr
r
ruleCheckBind RuleCheckEnv
env (Rec [(Var, CoreExpr)]
prs)    = [Bag SDoc] -> Bag SDoc
forall a. [Bag a] -> Bag a
unionManyBags [RuleCheckEnv -> CoreExpr -> Bag SDoc
ruleCheck RuleCheckEnv
env CoreExpr
r | (Var
_,CoreExpr
r) <- [(Var, CoreExpr)]
prs]

ruleCheck :: RuleCheckEnv -> CoreExpr -> Bag SDoc
ruleCheck :: RuleCheckEnv -> CoreExpr -> Bag SDoc
ruleCheck RuleCheckEnv
_   (Var Var
_)       = Bag SDoc
forall a. Bag a
emptyBag
ruleCheck RuleCheckEnv
_   (Lit Literal
_)       = Bag SDoc
forall a. Bag a
emptyBag
ruleCheck RuleCheckEnv
_   (Type Kind
_)      = Bag SDoc
forall a. Bag a
emptyBag
ruleCheck RuleCheckEnv
_   (Coercion Coercion
_)  = Bag SDoc
forall a. Bag a
emptyBag
ruleCheck RuleCheckEnv
env (App CoreExpr
f CoreExpr
a)     = RuleCheckEnv -> CoreExpr -> [CoreExpr] -> Bag SDoc
ruleCheckApp RuleCheckEnv
env (CoreExpr -> CoreExpr -> CoreExpr
forall b. Expr b -> Expr b -> Expr b
App CoreExpr
f CoreExpr
a) []
ruleCheck RuleCheckEnv
env (Tick CoreTickish
_ CoreExpr
e)  = RuleCheckEnv -> CoreExpr -> Bag SDoc
ruleCheck RuleCheckEnv
env CoreExpr
e
ruleCheck RuleCheckEnv
env (Cast CoreExpr
e Coercion
_)    = RuleCheckEnv -> CoreExpr -> Bag SDoc
ruleCheck RuleCheckEnv
env CoreExpr
e
ruleCheck RuleCheckEnv
env (Let CoreBind
bd CoreExpr
e)    = RuleCheckEnv -> CoreBind -> Bag SDoc
ruleCheckBind RuleCheckEnv
env CoreBind
bd Bag SDoc -> Bag SDoc -> Bag SDoc
forall a. Bag a -> Bag a -> Bag a
`unionBags` RuleCheckEnv -> CoreExpr -> Bag SDoc
ruleCheck RuleCheckEnv
env CoreExpr
e
ruleCheck RuleCheckEnv
env (Lam Var
_ CoreExpr
e)     = RuleCheckEnv -> CoreExpr -> Bag SDoc
ruleCheck RuleCheckEnv
env CoreExpr
e
ruleCheck RuleCheckEnv
env (Case CoreExpr
e Var
_ Kind
_ [Alt Var]
as) = RuleCheckEnv -> CoreExpr -> Bag SDoc
ruleCheck RuleCheckEnv
env CoreExpr
e Bag SDoc -> Bag SDoc -> Bag SDoc
forall a. Bag a -> Bag a -> Bag a
`unionBags`
                                [Bag SDoc] -> Bag SDoc
forall a. [Bag a] -> Bag a
unionManyBags [RuleCheckEnv -> CoreExpr -> Bag SDoc
ruleCheck RuleCheckEnv
env CoreExpr
r | Alt AltCon
_ [Var]
_ CoreExpr
r <- [Alt Var]
as]

ruleCheckApp :: RuleCheckEnv -> Expr CoreBndr -> [Arg CoreBndr] -> Bag SDoc
ruleCheckApp :: RuleCheckEnv -> CoreExpr -> [CoreExpr] -> Bag SDoc
ruleCheckApp RuleCheckEnv
env (App CoreExpr
f CoreExpr
a) [CoreExpr]
as = RuleCheckEnv -> CoreExpr -> Bag SDoc
ruleCheck RuleCheckEnv
env CoreExpr
a Bag SDoc -> Bag SDoc -> Bag SDoc
forall a. Bag a -> Bag a -> Bag a
`unionBags` RuleCheckEnv -> CoreExpr -> [CoreExpr] -> Bag SDoc
ruleCheckApp RuleCheckEnv
env CoreExpr
f (CoreExpr
aCoreExpr -> [CoreExpr] -> [CoreExpr]
forall a. a -> [a] -> [a]
:[CoreExpr]
as)
ruleCheckApp RuleCheckEnv
env (Var Var
f) [CoreExpr]
as   = RuleCheckEnv -> Var -> [CoreExpr] -> Bag SDoc
ruleCheckFun RuleCheckEnv
env Var
f [CoreExpr]
as
ruleCheckApp RuleCheckEnv
env CoreExpr
other [CoreExpr]
_      = RuleCheckEnv -> CoreExpr -> Bag SDoc
ruleCheck RuleCheckEnv
env CoreExpr
other

ruleCheckFun :: RuleCheckEnv -> Id -> [CoreExpr] -> Bag SDoc
-- Produce a report for all rules matching the predicate
-- saying why it doesn't match the specified application

ruleCheckFun :: RuleCheckEnv -> Var -> [CoreExpr] -> Bag SDoc
ruleCheckFun RuleCheckEnv
env Var
fn [CoreExpr]
args
  | [CoreRule] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [CoreRule]
name_match_rules = Bag SDoc
forall a. Bag a
emptyBag
  | Bool
otherwise             = SDoc -> Bag SDoc
forall a. a -> Bag a
unitBag (RuleCheckEnv -> Var -> [CoreExpr] -> [CoreRule] -> SDoc
ruleAppCheck_help RuleCheckEnv
env Var
fn [CoreExpr]
args [CoreRule]
name_match_rules)
  where
    name_match_rules :: [CoreRule]
name_match_rules = (CoreRule -> Bool) -> [CoreRule] -> [CoreRule]
forall a. (a -> Bool) -> [a] -> [a]
filter CoreRule -> Bool
match (RuleCheckEnv -> Var -> [CoreRule]
rc_rules RuleCheckEnv
env Var
fn)
    match :: CoreRule -> Bool
match CoreRule
rule = RuleCheckEnv -> String
rc_pattern RuleCheckEnv
env String -> String -> Bool
forall a. Eq a => [a] -> [a] -> Bool
`isPrefixOf` RuleName -> String
unpackFS (CoreRule -> RuleName
ruleName CoreRule
rule)

ruleAppCheck_help :: RuleCheckEnv -> Id -> [CoreExpr] -> [CoreRule] -> SDoc
ruleAppCheck_help :: RuleCheckEnv -> Var -> [CoreExpr] -> [CoreRule] -> SDoc
ruleAppCheck_help RuleCheckEnv
env Var
fn [CoreExpr]
args [CoreRule]
rules
  =     -- The rules match the pattern, so we want to print something
    [SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat [String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Expression:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> CoreExpr -> SDoc
forall a. Outputable a => a -> SDoc
ppr (CoreExpr -> [CoreExpr] -> CoreExpr
forall b. Expr b -> [Expr b] -> Expr b
mkApps (Var -> CoreExpr
forall b. Var -> Expr b
Var Var
fn) [CoreExpr]
args),
          [SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat ((CoreRule -> SDoc) -> [CoreRule] -> [SDoc]
forall a b. (a -> b) -> [a] -> [b]
map CoreRule -> SDoc
check_rule [CoreRule]
rules)]
  where
    n_args :: Arity
n_args = [CoreExpr] -> Arity
forall a. [a] -> Arity
forall (t :: * -> *) a. Foldable t => t a -> Arity
length [CoreExpr]
args
    i_args :: [(CoreExpr, Arity)]
i_args = [CoreExpr]
args [CoreExpr] -> [Arity] -> [(CoreExpr, Arity)]
forall a b. [a] -> [b] -> [(a, b)]
`zip` [Arity
1::Int ..]
    rough_args :: [Maybe Name]
rough_args = (CoreExpr -> Maybe Name) -> [CoreExpr] -> [Maybe Name]
forall a b. (a -> b) -> [a] -> [b]
map CoreExpr -> Maybe Name
roughTopName [CoreExpr]
args

    check_rule :: CoreRule -> SDoc
check_rule CoreRule
rule = CoreRule -> SDoc
forall {doc}. IsLine doc => CoreRule -> doc
rule_herald CoreRule
rule SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<> SDoc
forall doc. IsLine doc => doc
colon SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> RuleOpts -> CoreRule -> SDoc
rule_info (RuleCheckEnv -> RuleOpts
rc_ropts RuleCheckEnv
env) CoreRule
rule

    rule_herald :: CoreRule -> doc
rule_herald (BuiltinRule { ru_name :: CoreRule -> RuleName
ru_name = RuleName
name })
        = String -> doc
forall doc. IsLine doc => String -> doc
text String
"Builtin rule" doc -> doc -> doc
forall doc. IsLine doc => doc -> doc -> doc
<+> doc -> doc
forall doc. IsLine doc => doc -> doc
doubleQuotes (RuleName -> doc
forall doc. IsLine doc => RuleName -> doc
ftext RuleName
name)
    rule_herald (Rule { ru_name :: CoreRule -> RuleName
ru_name = RuleName
name })
        = String -> doc
forall doc. IsLine doc => String -> doc
text String
"Rule" doc -> doc -> doc
forall doc. IsLine doc => doc -> doc -> doc
<+> doc -> doc
forall doc. IsLine doc => doc -> doc
doubleQuotes (RuleName -> doc
forall doc. IsLine doc => RuleName -> doc
ftext RuleName
name)

    rule_info :: RuleOpts -> CoreRule -> SDoc
rule_info RuleOpts
opts CoreRule
rule
        | Just CoreExpr
_ <- RuleOpts
-> InScopeEnv
-> (Activation -> Bool)
-> Var
-> [CoreExpr]
-> [Maybe Name]
-> CoreRule
-> Maybe CoreExpr
matchRule RuleOpts
opts (InScopeSet -> IdUnfoldingFun -> InScopeEnv
ISE InScopeSet
emptyInScopeSet (RuleCheckEnv -> IdUnfoldingFun
rc_id_unf RuleCheckEnv
env))
                              Activation -> Bool
noBlackList Var
fn [CoreExpr]
args [Maybe Name]
rough_args CoreRule
rule
        = String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"matches (which is very peculiar!)"

    rule_info RuleOpts
_ (BuiltinRule {}) = String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"does not match"

    rule_info RuleOpts
_ (Rule { ru_act :: CoreRule -> Activation
ru_act = Activation
act,
                        ru_bndrs :: CoreRule -> [Var]
ru_bndrs = [Var]
rule_bndrs, ru_args :: CoreRule -> [CoreExpr]
ru_args = [CoreExpr]
rule_args})
        | Bool -> Bool
not (RuleCheckEnv -> Activation -> Bool
rc_is_active RuleCheckEnv
env Activation
act)  = String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"active only in later phase"
        | Arity
n_args Arity -> Arity -> Bool
forall a. Ord a => a -> a -> Bool
< Arity
n_rule_args        = String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"too few arguments"
        | Arity
n_mismatches Arity -> Arity -> Bool
forall a. Eq a => a -> a -> Bool
== Arity
n_rule_args = String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"no arguments match"
        | Arity
n_mismatches Arity -> Arity -> Bool
forall a. Eq a => a -> a -> Bool
== Arity
0           = String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"all arguments match (considered individually), but rule as a whole does not"
        | Bool
otherwise                   = String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"arguments" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> [Arity] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [Arity]
mismatches SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"do not match (1-indexing)"
        where
          n_rule_args :: Arity
n_rule_args  = [CoreExpr] -> Arity
forall a. [a] -> Arity
forall (t :: * -> *) a. Foldable t => t a -> Arity
length [CoreExpr]
rule_args
          n_mismatches :: Arity
n_mismatches = [Arity] -> Arity
forall a. [a] -> Arity
forall (t :: * -> *) a. Foldable t => t a -> Arity
length [Arity]
mismatches
          mismatches :: [Arity]
mismatches   = [Arity
i | (CoreExpr
rule_arg, (CoreExpr
arg,Arity
i)) <- [CoreExpr]
rule_args [CoreExpr]
-> [(CoreExpr, Arity)] -> [(CoreExpr, (CoreExpr, Arity))]
forall a b. [a] -> [b] -> [(a, b)]
`zip` [(CoreExpr, Arity)]
i_args,
                              Bool -> Bool
not (Maybe RuleSubst -> Bool
forall a. Maybe a -> Bool
isJust (CoreExpr -> CoreExpr -> Maybe RuleSubst
match_fn CoreExpr
rule_arg CoreExpr
arg))]

          lhs_fvs :: VarSet
lhs_fvs = [CoreExpr] -> VarSet
exprsFreeVars [CoreExpr]
rule_args     -- Includes template tyvars
          match_fn :: CoreExpr -> CoreExpr -> Maybe RuleSubst
match_fn CoreExpr
rule_arg CoreExpr
arg = RuleMatchEnv
-> RuleSubst
-> CoreExpr
-> CoreExpr
-> MCoercion
-> Maybe RuleSubst
match RuleMatchEnv
renv RuleSubst
emptyRuleSubst CoreExpr
rule_arg CoreExpr
arg MCoercion
MRefl
                where
                  in_scope :: InScopeSet
in_scope = VarSet -> InScopeSet
mkInScopeSet (VarSet
lhs_fvs VarSet -> VarSet -> VarSet
`unionVarSet` CoreExpr -> VarSet
exprFreeVars CoreExpr
arg)
                  renv :: RuleMatchEnv
renv = RV { rv_lcl :: RnEnv2
rv_lcl   = InScopeSet -> RnEnv2
mkRnEnv2 InScopeSet
in_scope
                            , rv_tmpls :: VarSet
rv_tmpls = [Var] -> VarSet
mkVarSet [Var]
rule_bndrs
                            , rv_fltR :: Subst
rv_fltR  = InScopeSet -> Subst
mkEmptySubst InScopeSet
in_scope
                            , rv_unf :: IdUnfoldingFun
rv_unf   = RuleCheckEnv -> IdUnfoldingFun
rc_id_unf RuleCheckEnv
env }