GHC/Builtin/PrimOps.hs

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

    \section[PrimOp]{Primitive operations (machine-level)}
    -}

    {-# LANGUAGE CPP #-}

    module GHC.Builtin.PrimOps (
            PrimOp(..), PrimOpVecCat(..), allThePrimOps,
            primOpType, primOpSig, primOpResultType,
            primOpTag, maxPrimOpTag, primOpOcc,
            primOpWrapperId,

            tagToEnumKey,

            primOpOutOfLine, primOpCodeSize,
            primOpOkForSpeculation, primOpOkForSideEffects,
            primOpIsCheap, primOpFixity, primOpDocs,
            primOpIsDiv,

            getPrimOpResultInfo,  isComparisonPrimOp, PrimOpResultInfo(..),

            PrimCall(..)
        ) where

    #include "HsVersions.h"

    import GHC.Prelude

    import GHC.Builtin.Types.Prim
    import GHC.Builtin.Types

    import GHC.Cmm.Type
    import GHC.Types.Demand
    import GHC.Types.Id      ( Id, mkVanillaGlobalWithInfo )
    import GHC.Types.Id.Info ( vanillaIdInfo, setCafInfo, CafInfo(NoCafRefs) )
    import GHC.Types.Name
    import GHC.Builtin.Names ( gHC_PRIMOPWRAPPERS )
    import GHC.Core.TyCon    ( TyCon, isPrimTyCon, PrimRep(..) )
    import GHC.Core.Type
    import GHC.Types.RepType ( tyConPrimRep1 )
    import GHC.Types.Basic   ( Arity, Boxity(..) )
    import GHC.Types.Fixity  ( Fixity(..), FixityDirection(..) )
    import GHC.Types.SrcLoc  ( wiredInSrcSpan )
    import GHC.Types.ForeignCall ( CLabelString )
    import GHC.Types.SourceText  ( SourceText(..) )
    import GHC.Types.Unique  ( Unique)
    import GHC.Builtin.Uniques (mkPrimOpIdUnique, mkPrimOpWrapperUnique )
    import GHC.Unit.Types    ( Unit )
    import GHC.Utils.Outputable
    import GHC.Data.FastString

    {-
    ************************************************************************
    *                                                                      *
    \subsection[PrimOp-datatype]{Datatype for @PrimOp@ (an enumeration)}
    *                                                                      *
    ************************************************************************

    These are in \tr{state-interface.verb} order.
    -}

    -- supplies:
    -- data PrimOp = ...
    #include "primop-data-decl.hs-incl"

    -- supplies
    -- primOpTag :: PrimOp -> Int
    #include "primop-tag.hs-incl"
    primOpTag _ = error "primOpTag: unknown primop"

    instance Eq PrimOp where
        op1 == op2 = primOpTag op1 == primOpTag op2

    instance Ord PrimOp where
        op1 <  op2 =  primOpTag op1 < primOpTag op2
        op1 <= op2 =  primOpTag op1 <= primOpTag op2
        op1 >= op2 =  primOpTag op1 >= primOpTag op2
        op1 >  op2 =  primOpTag op1 > primOpTag op2
        op1 `compare` op2 | op1 < op2  = LT
                          | op1 == op2 = EQ
                          | otherwise  = GT

    instance Outputable PrimOp where
        ppr op = pprPrimOp op

    data PrimOpVecCat = IntVec
                      | WordVec
                      | FloatVec

    -- An @Enum@-derived list would be better; meanwhile... (ToDo)

    allThePrimOps :: [PrimOp]
    allThePrimOps =
    #include "primop-list.hs-incl"

    tagToEnumKey :: Unique
    tagToEnumKey = mkPrimOpIdUnique (primOpTag TagToEnumOp)

    {-
    ************************************************************************
    *                                                                      *
    \subsection[PrimOp-info]{The essential info about each @PrimOp@}
    *                                                                      *
    ************************************************************************
    -}

    data PrimOpInfo
      = Compare     OccName         -- string :: T -> T -> Int#
                    Type
      | GenPrimOp   OccName         -- string :: \/a1..an . T1 -> .. -> Tk -> T
                    [TyVar]
                    [Type]
                    Type

    mkCompare :: FastString -> Type -> PrimOpInfo
    mkCompare str ty = Compare (mkVarOccFS str) ty

    mkGenPrimOp :: FastString -> [TyVar] -> [Type] -> Type -> PrimOpInfo
    mkGenPrimOp str tvs tys ty = GenPrimOp (mkVarOccFS str) tvs tys ty

    {-
    ************************************************************************
    *                                                                      *
    \subsubsection{Strictness}
    *                                                                      *
    ************************************************************************

    Not all primops are strict!
    -}

    primOpStrictness :: PrimOp -> Arity -> StrictSig
            -- See Demand.StrictnessInfo for discussion of what the results
            -- The arity should be the arity of the primop; that's why
            -- this function isn't exported.
    #include "primop-strictness.hs-incl"

    {-
    ************************************************************************
    *                                                                      *
    \subsubsection{Fixity}
    *                                                                      *
    ************************************************************************
    -}

    primOpFixity :: PrimOp -> Maybe Fixity
    #include "primop-fixity.hs-incl"

    {-
    ************************************************************************
    *                                                                      *
    \subsubsection{Docs}
    *                                                                      *
    ************************************************************************

    See Note [GHC.Prim Docs]
    -}

    primOpDocs :: [(String, String)]
    #include "primop-docs.hs-incl"

    {-
    ************************************************************************
    *                                                                      *
    \subsubsection[PrimOp-comparison]{PrimOpInfo basic comparison ops}
    *                                                                      *
    ************************************************************************

    @primOpInfo@ gives all essential information (from which everything
    else, notably a type, can be constructed) for each @PrimOp@.
    -}

    primOpInfo :: PrimOp -> PrimOpInfo
    #include "primop-primop-info.hs-incl"
    primOpInfo _ = error "primOpInfo: unknown primop"

    {-
    Here are a load of comments from the old primOp info:

    A @Word#@ is an unsigned @Int#@.

    @decodeFloat#@ is given w/ Integer-stuff (it's similar).

    @decodeDouble#@ is given w/ Integer-stuff (it's similar).

    Decoding of floating-point numbers is sorta Integer-related.  Encoding
    is done with plain ccalls now (see PrelNumExtra.hs).

    A @Weak@ Pointer is created by the @mkWeak#@ primitive:

            mkWeak# :: k -> v -> f -> State# RealWorld
                            -> (# State# RealWorld, Weak# v #)

    In practice, you'll use the higher-level

            data Weak v = Weak# v
            mkWeak :: k -> v -> IO () -> IO (Weak v)

    The following operation dereferences a weak pointer.  The weak pointer
    may have been finalized, so the operation returns a result code which
    must be inspected before looking at the dereferenced value.

            deRefWeak# :: Weak# v -> State# RealWorld ->
                            (# State# RealWorld, v, Int# #)

    Only look at v if the Int# returned is /= 0 !!

    The higher-level op is

            deRefWeak :: Weak v -> IO (Maybe v)

    Weak pointers can be finalized early by using the finalize# operation:

            finalizeWeak# :: Weak# v -> State# RealWorld ->
                               (# State# RealWorld, Int#, IO () #)

    The Int# returned is either

            0 if the weak pointer has already been finalized, or it has no
              finalizer (the third component is then invalid).

            1 if the weak pointer is still alive, with the finalizer returned
              as the third component.

    A {\em stable name/pointer} is an index into a table of stable name
    entries.  Since the garbage collector is told about stable pointers,
    it is safe to pass a stable pointer to external systems such as C
    routines.

    \begin{verbatim}
    makeStablePtr#  :: a -> State# RealWorld -> (# State# RealWorld, StablePtr# a #)
    freeStablePtr   :: StablePtr# a -> State# RealWorld -> State# RealWorld
    deRefStablePtr# :: StablePtr# a -> State# RealWorld -> (# State# RealWorld, a #)
    eqStablePtr#    :: StablePtr# a -> StablePtr# a -> Int#
    \end{verbatim}

    It may seem a bit surprising that @makeStablePtr#@ is a @IO@
    operation since it doesn't (directly) involve IO operations.  The
    reason is that if some optimisation pass decided to duplicate calls to
    @makeStablePtr#@ and we only pass one of the stable pointers over, a
    massive space leak can result.  Putting it into the IO monad
    prevents this.  (Another reason for putting them in a monad is to
    ensure correct sequencing wrt the side-effecting @freeStablePtr@
    operation.)

    An important property of stable pointers is that if you call
    makeStablePtr# twice on the same object you get the same stable
    pointer back.

    Note that we can implement @freeStablePtr#@ using @_ccall_@ (and,
    besides, it's not likely to be used from Haskell) so it's not a
    primop.

    Question: Why @RealWorld@ - won't any instance of @_ST@ do the job? [ADR]

    Stable Names
    ~~~~~~~~~~~~

    A stable name is like a stable pointer, but with three important differences:

            (a) You can't deRef one to get back to the original object.
            (b) You can convert one to an Int.
            (c) You don't need to 'freeStableName'

    The existence of a stable name doesn't guarantee to keep the object it
    points to alive (unlike a stable pointer), hence (a).

    Invariants:

            (a) makeStableName always returns the same value for a given
                object (same as stable pointers).

            (b) if two stable names are equal, it implies that the objects
                from which they were created were the same.

            (c) stableNameToInt always returns the same Int for a given
                stable name.

    These primops are pretty weird.

            tagToEnum# :: Int -> a    (result type must be an enumerated type)

    The constraints aren't currently checked by the front end, but the
    code generator will fall over if they aren't satisfied.

    ************************************************************************
    *                                                                      *
                Which PrimOps are out-of-line
    *                                                                      *
    ************************************************************************

    Some PrimOps need to be called out-of-line because they either need to
    perform a heap check or they block.
    -}

    primOpOutOfLine :: PrimOp -> Bool
    #include "primop-out-of-line.hs-incl"

    {-
    ************************************************************************
    *                                                                      *
                Failure and side effects
    *                                                                      *
    ************************************************************************

    Note [Checking versus non-checking primops]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

      In GHC primops break down into two classes:

       a. Checking primops behave, for instance, like division. In this
          case the primop may throw an exception (e.g. division-by-zero)
          and is consequently is marked with the can_fail flag described below.
          The ability to fail comes at the expense of precluding some optimizations.

       b. Non-checking primops behavior, for instance, like addition. While
          addition can overflow it does not produce an exception. So can_fail is
          set to False, and we get more optimisation opportunities.  But we must
          never throw an exception, so we cannot rewrite to a call to error.

      It is important that a non-checking primop never be transformed in a way that
      would cause it to bottom. Doing so would violate Core's let/app invariant
      (see Note [Core let/app invariant] in GHC.Core) which is critical to
      the simplifier's ability to float without fear of changing program meaning.

    Note [PrimOp can_fail and has_side_effects]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Both can_fail and has_side_effects mean that the primop has
    some effect that is not captured entirely by its result value.

    ----------  has_side_effects ---------------------
    A primop "has_side_effects" if it has some *write* effect, visible
    elsewhere
        - writing to the world (I/O)
        - writing to a mutable data structure (writeIORef)
        - throwing a synchronous Haskell exception

    Often such primops have a type like
       State -> input -> (State, output)
    so the state token guarantees ordering.  In general we rely *only* on
    data dependencies of the state token to enforce write-effect ordering

     * NB1: if you inline unsafePerformIO, you may end up with
       side-effecting ops whose 'state' output is discarded.
       And programmers may do that by hand; see #9390.
       That is why we (conservatively) do not discard write-effecting
       primops even if both their state and result is discarded.

     * NB2: We consider primops, such as raiseIO#, that can raise a
       (Haskell) synchronous exception to "have_side_effects" but not
       "can_fail".  We must be careful about not discarding such things;
       see the paper "A semantics for imprecise exceptions".

     * NB3: *Read* effects (like reading an IORef) don't count here,
       because it doesn't matter if we don't do them, or do them more than
       once.  *Sequencing* is maintained by the data dependency of the state
       token.

    ----------  can_fail ----------------------------
    A primop "can_fail" if it can fail with an *unchecked* exception on
    some elements of its input domain. Main examples:
       division (fails on zero denominator)
       array indexing (fails if the index is out of bounds)

    An "unchecked exception" is one that is an outright error, (not
    turned into a Haskell exception,) such as seg-fault or
    divide-by-zero error.  Such can_fail primops are ALWAYS surrounded
    with a test that checks for the bad cases, but we need to be
    very careful about code motion that might move it out of
    the scope of the test.

    Note [Transformations affected by can_fail and has_side_effects]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The can_fail and has_side_effects properties have the following effect
    on program transformations.  Summary table is followed by details.

                can_fail     has_side_effects
    Discard        YES           NO
    Float in       YES           YES
    Float out      NO            NO
    Duplicate      YES           NO

    * Discarding.   case (a `op` b) of _ -> rhs  ===>   rhs
      You should not discard a has_side_effects primop; e.g.
         case (writeIntArray# a i v s of (# _, _ #) -> True
      Arguably you should be able to discard this, since the
      returned stat token is not used, but that relies on NEVER
      inlining unsafePerformIO, and programmers sometimes write
      this kind of stuff by hand (#9390).  So we (conservatively)
      never discard a has_side_effects primop.

      However, it's fine to discard a can_fail primop.  For example
         case (indexIntArray# a i) of _ -> True
      We can discard indexIntArray#; it has can_fail, but not
      has_side_effects; see #5658 which was all about this.
      Notice that indexIntArray# is (in a more general handling of
      effects) read effect, but we don't care about that here, and
      treat read effects as *not* has_side_effects.

      Similarly (a `/#` b) can be discarded.  It can seg-fault or
      cause a hardware exception, but not a synchronous Haskell
      exception.

      Synchronous Haskell exceptions, e.g. from raiseIO#, are treated
      as has_side_effects and hence are not discarded.

    * Float in.  You can float a can_fail or has_side_effects primop
      *inwards*, but not inside a lambda (see Duplication below).

    * Float out.  You must not float a can_fail primop *outwards* lest
      you escape the dynamic scope of the test.  Example:
          case d ># 0# of
            True  -> case x /# d of r -> r +# 1
            False -> 0
      Here we must not float the case outwards to give
          case x/# d of r ->
          case d ># 0# of
            True  -> r +# 1
            False -> 0

      Nor can you float out a has_side_effects primop.  For example:
           if blah then case writeMutVar# v True s0 of (# s1 #) -> s1
                   else s0
      Notice that s0 is mentioned in both branches of the 'if', but
      only one of these two will actually be consumed.  But if we
      float out to
          case writeMutVar# v True s0 of (# s1 #) ->
          if blah then s1 else s0
      the writeMutVar will be performed in both branches, which is
      utterly wrong.

    * Duplication.  You cannot duplicate a has_side_effect primop.  You
      might wonder how this can occur given the state token threading, but
      just look at Control.Monad.ST.Lazy.Imp.strictToLazy!  We get
      something like this
            p = case readMutVar# s v of
                  (# s', r #) -> (State# s', r)
            s' = case p of (s', r) -> s'
            r  = case p of (s', r) -> r

      (All these bindings are boxed.)  If we inline p at its two call
      sites, we get a catastrophe: because the read is performed once when
      s' is demanded, and once when 'r' is demanded, which may be much
      later.  Utterly wrong.  #3207 is real example of this happening.

      However, it's fine to duplicate a can_fail primop.  That is really
      the only difference between can_fail and has_side_effects.

    Note [Implementation: how can_fail/has_side_effects affect transformations]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    How do we ensure that floating/duplication/discarding are done right
    in the simplifier?

    Two main predicates on primpops test these flags:
      primOpOkForSideEffects <=> not has_side_effects
      primOpOkForSpeculation <=> not (has_side_effects || can_fail)

      * The "no-float-out" thing is achieved by ensuring that we never
        let-bind a can_fail or has_side_effects primop.  The RHS of a
        let-binding (which can float in and out freely) satisfies
        exprOkForSpeculation; this is the let/app invariant.  And
        exprOkForSpeculation is false of can_fail and has_side_effects.

      * So can_fail and has_side_effects primops will appear only as the
        scrutinees of cases, and that's why the FloatIn pass is capable
        of floating case bindings inwards.

      * The no-duplicate thing is done via primOpIsCheap, by making
        has_side_effects things (very very very) not-cheap!
    -}

    primOpHasSideEffects :: PrimOp -> Bool
    #include "primop-has-side-effects.hs-incl"

    primOpCanFail :: PrimOp -> Bool
    #include "primop-can-fail.hs-incl"

    primOpOkForSpeculation :: PrimOp -> Bool
      -- See Note [PrimOp can_fail and has_side_effects]
      -- See comments with GHC.Core.Utils.exprOkForSpeculation
      -- primOpOkForSpeculation => primOpOkForSideEffects
    primOpOkForSpeculation op
      =  primOpOkForSideEffects op
      && not (primOpOutOfLine op || primOpCanFail op)
        -- I think the "out of line" test is because out of line things can
        -- be expensive (eg sine, cosine), and so we may not want to speculate them

    primOpOkForSideEffects :: PrimOp -> Bool
    primOpOkForSideEffects op
      = not (primOpHasSideEffects op)

    {-
    Note [primOpIsCheap]
    ~~~~~~~~~~~~~~~~~~~~

    @primOpIsCheap@, as used in GHC.Core.Opt.Simplify.Utils.  For now (HACK
    WARNING), we just borrow some other predicates for a
    what-should-be-good-enough test.  "Cheap" means willing to call it more
    than once, and/or push it inside a lambda.  The latter could change the
    behaviour of 'seq' for primops that can fail, so we don't treat them as cheap.
    -}

    primOpIsCheap :: PrimOp -> Bool
    -- See Note [PrimOp can_fail and has_side_effects]
    primOpIsCheap op = primOpOkForSpeculation op
    -- In March 2001, we changed this to
    --      primOpIsCheap op = False
    -- thereby making *no* primops seem cheap.  But this killed eta
    -- expansion on case (x ==# y) of True -> \s -> ...
    -- which is bad.  In particular a loop like
    --      doLoop n = loop 0
    --     where
    --         loop i | i == n    = return ()
    --                | otherwise = bar i >> loop (i+1)
    -- allocated a closure every time round because it doesn't eta expand.
    --
    -- The problem that originally gave rise to the change was
    --      let x = a +# b *# c in x +# x
    -- were we don't want to inline x. But primopIsCheap doesn't control
    -- that (it's exprIsDupable that does) so the problem doesn't occur
    -- even if primOpIsCheap sometimes says 'True'.

    -- | True of dyadic operators that can fail only if the second arg is zero!
    --
    -- This function probably belongs in an automagically generated file.. but it's
    -- such a special case I thought I'd leave it here for now.
    primOpIsDiv :: PrimOp -> Bool
    primOpIsDiv op = case op of

      -- TODO: quotRemWord2, Int64, Word64
      IntQuotOp       -> True
      Int8QuotOp      -> True
      Int16QuotOp     -> True
      Int32QuotOp     -> True

      IntRemOp        -> True
      Int8RemOp       -> True
      Int16RemOp      -> True
      Int32RemOp      -> True

      IntQuotRemOp    -> True
      Int8QuotRemOp   -> True
      Int16QuotRemOp  -> True
      Int32QuotRemOp  -> True

      WordQuotOp      -> True
      Word8QuotOp     -> True
      Word16QuotOp    -> True
      Word32QuotOp    -> True

      WordRemOp       -> True
      Word8RemOp      -> True
      Word16RemOp     -> True
      Word32RemOp     -> True

      WordQuotRemOp   -> True
      Word8QuotRemOp  -> True
      Word16QuotRemOp -> True
      Word32QuotRemOp -> True

      FloatDivOp      -> True
      DoubleDivOp     -> True
      _               -> False

    {-
    ************************************************************************
    *                                                                      *
                   PrimOp code size
    *                                                                      *
    ************************************************************************

    primOpCodeSize
    ~~~~~~~~~~~~~~
    Gives an indication of the code size of a primop, for the purposes of
    calculating unfolding sizes; see GHC.Core.Unfold.sizeExpr.
    -}

    primOpCodeSize :: PrimOp -> Int
    #include "primop-code-size.hs-incl"

    primOpCodeSizeDefault :: Int
    primOpCodeSizeDefault = 1
      -- GHC.Core.Unfold.primOpSize already takes into account primOpOutOfLine
      -- and adds some further costs for the args in that case.

    primOpCodeSizeForeignCall :: Int
    primOpCodeSizeForeignCall = 4

    {-
    ************************************************************************
    *                                                                      *
                   PrimOp types
    *                                                                      *
    ************************************************************************
    -}

    primOpType :: PrimOp -> Type  -- you may want to use primOpSig instead
    primOpType op
      = case primOpInfo op of
        Compare _occ ty -> compare_fun_ty ty

        GenPrimOp _occ tyvars arg_tys res_ty ->
            mkSpecForAllTys tyvars (mkVisFunTysMany arg_tys res_ty)

    primOpResultType :: PrimOp -> Type
    primOpResultType op
      = case primOpInfo op of
        Compare _occ _ty -> intPrimTy
        GenPrimOp _occ _tyvars _arg_tys res_ty -> res_ty

    primOpOcc :: PrimOp -> OccName
    primOpOcc op = case primOpInfo op of
                   Compare   occ _     -> occ
                   GenPrimOp occ _ _ _ -> occ

    {- Note [Primop wrappers]
    ~~~~~~~~~~~~~~~~~~~~~~~~~

    To support (limited) use of primops in GHCi genprimopcode generates the
    GHC.PrimopWrappers module. This module contains a "primop wrapper"
    binding for each primop. These are standard Haskell functions mirroring the
    types of the primops they wrap. For instance, in the case of plusInt# we would
    have:

        module GHC.PrimopWrappers where
        import GHC.Prim as P

        plusInt# :: Int# -> Int# -> Int#
        plusInt# a b = P.plusInt# a b

    The Id for the wrapper of a primop can be found using
    'GHC.Builtin.PrimOp.primOpWrapperId'. However, GHCi does not use this mechanism
    to link primops; it rather does a rather hacky symbol lookup (see
    GHC.ByteCode.Linker.primopToCLabel). TODO: Perhaps this should be changed?

    Note that these wrappers aren't *quite*
    as expressive as their unwrapped breathern in that they may exhibit less levity
    polymorphism. For instance, consider the case of mkWeakNoFinalizer# which has
    type:

        mkWeakNoFinalizer# :: forall (r :: RuntimeRep) (k :: TYPE r) (v :: Type).
                              k -> v
                           -> State# RealWorld
                           -> (# State# RealWorld, Weak# v #)

    Naively we could generate a wrapper of the form,

        mkWeakNoFinalizer# k v s = GHC.Prim.mkWeakNoFinalizer# k v s

    However, this would require that 'k' bind the levity-polymorphic key,
    which is disallowed by our levity polymorphism validity checks (see Note
    [Levity polymorphism invariants] in GHC.Core). Consequently, we give the
    wrapper the simpler, less polymorphic type

        mkWeakNoFinalizer# :: forall (k :: Type) (v :: Type).
                              k -> v
                           -> State# RealWorld
                           -> (# State# RealWorld, Weak# v #)

    This simplification tends to be good enough for GHCi uses given that there are
    few levity polymorphic primops and we do little simplification on interpreted
    code anyways.

    TODO: This behavior is actually wrong; a program becomes ill-typed upon
    replacing a real primop occurrence with one of its wrapper due to the fact that
    the former has an additional type binder. Hmmm....

    Note [Eta expanding primops]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    STG requires that primop applications be saturated. This makes code generation
    significantly simpler since otherwise we would need to define a calling
    convention for curried applications that can accommodate levity polymorphism.

    To ensure saturation, CorePrep eta expands expand all primop applications as
    described in Note [Eta expansion of hasNoBinding things in CorePrep] in
    GHC.Core.Prep.

    Historical Note:

    For a short period around GHC 8.8 we rewrote unsaturated primop applications to
    rather use the primop's wrapper (see Note [Primop wrappers] in
    GHC.Builtin.PrimOps) instead of eta expansion. This was because at the time
    CoreTidy would try to predict the CAFfyness of bindings that would be produced
    by CorePrep for inclusion in interface files. Eta expanding during CorePrep
    proved to be very difficult to predict, leading to nasty inconsistencies in
    CAFfyness determinations (see #16846).

    Thankfully, we now no longer try to predict CAFfyness but rather compute it on
    GHC STG (see Note [SRTs] in GHC.Cmm.Info.Build) and inject it into the interface
    file after code generation (see TODO: Refer to whatever falls out of #18096).
    This is much simpler and avoids the potential for inconsistency, allowing us to
    return to the somewhat simpler eta expansion approach for unsaturated primops.

    See #18079.
    -}

    -- | Returns the 'Id' of the wrapper associated with the given 'PrimOp'.
    -- See Note [Primop wrappers].
    primOpWrapperId :: PrimOp -> Id
    primOpWrapperId op = mkVanillaGlobalWithInfo name ty info
      where
        info = setCafInfo vanillaIdInfo NoCafRefs
        name = mkExternalName uniq gHC_PRIMOPWRAPPERS (primOpOcc op) wiredInSrcSpan
        uniq = mkPrimOpWrapperUnique (primOpTag op)
        ty   = primOpType op

    isComparisonPrimOp :: PrimOp -> Bool
    isComparisonPrimOp op = case primOpInfo op of
                              Compare {}   -> True
                              GenPrimOp {} -> False

    -- primOpSig is like primOpType but gives the result split apart:
    -- (type variables, argument types, result type)
    -- It also gives arity, strictness info

    primOpSig :: PrimOp -> ([TyVar], [Type], Type, Arity, StrictSig)
    primOpSig op
      = (tyvars, arg_tys, res_ty, arity, primOpStrictness op arity)
      where
        arity = length arg_tys
        (tyvars, arg_tys, res_ty)
          = case (primOpInfo op) of
            Compare   _occ ty                    -> ([],     [ty,ty], intPrimTy)
            GenPrimOp _occ tyvars arg_tys res_ty -> (tyvars, arg_tys, res_ty   )

    data PrimOpResultInfo
      = ReturnsPrim     PrimRep
      | ReturnsAlg      TyCon

    -- Some PrimOps need not return a manifest primitive or algebraic value
    -- (i.e. they might return a polymorphic value).  These PrimOps *must*
    -- be out of line, or the code generator won't work.

    getPrimOpResultInfo :: PrimOp -> PrimOpResultInfo
    getPrimOpResultInfo op
      = case (primOpInfo op) of
          Compare _ _                         -> ReturnsPrim (tyConPrimRep1 intPrimTyCon)
          GenPrimOp _ _ _ ty | isPrimTyCon tc -> ReturnsPrim (tyConPrimRep1 tc)
                             | otherwise      -> ReturnsAlg tc
                             where
                               tc = tyConAppTyCon ty
                            -- All primops return a tycon-app result
                            -- The tycon can be an unboxed tuple or sum, though,
                            -- which gives rise to a ReturnAlg

    {-
    We do not currently make use of whether primops are commutable.

    We used to try to move constants to the right hand side for strength
    reduction.
    -}

    {-
    commutableOp :: PrimOp -> Bool
    #include "primop-commutable.hs-incl"
    -}

    -- Utils:

    compare_fun_ty :: Type -> Type
    compare_fun_ty ty = mkVisFunTysMany [ty, ty] intPrimTy

    -- Output stuff:

    pprPrimOp  :: PrimOp -> SDoc
    pprPrimOp other_op = pprOccName (primOpOcc other_op)

    {-
    ************************************************************************
    *                                                                      *
    \subsubsection[PrimCall]{User-imported primitive calls}
    *                                                                      *
    ************************************************************************
    -}

    data PrimCall = PrimCall CLabelString Unit

    instance Outputable PrimCall where
      ppr (PrimCall lbl pkgId)
            = text "__primcall" <+> ppr pkgId <+> ppr lbl