+
+%************************************************************************
+%* *
+\subsection{Un-definable}
+%* *
+%************************************************************************
+
+These Ids can't be defined in Haskell. They could be defined in
+unfoldings in the wired-in GHC.Prim interface file, but we'd have to
+ensure that they were definitely, definitely inlined, because there is
+no curried identifier for them. That's what mkCompulsoryUnfolding
+does. If we had a way to get a compulsory unfolding from an interface
+file, we could do that, but we don't right now.
+
+unsafeCoerce# isn't so much a PrimOp as a phantom identifier, that
+just gets expanded into a type coercion wherever it occurs. Hence we
+add it as a built-in Id with an unfolding here.
+
+The type variables we use here are "open" type variables: this means
+they can unify with both unlifted and lifted types. Hence we provide
+another gun with which to shoot yourself in the foot.
+
+\begin{code}
+-- unsafeCoerce# :: forall a b. a -> b
+unsafeCoerceId
+ = pcMiscPrelId unsafeCoerceName ty info
+ where
+ info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
+
+
+ ty = mkForAllTys [openAlphaTyVar,openBetaTyVar]
+ (mkFunTy openAlphaTy openBetaTy)
+ [x] = mkTemplateLocals [openAlphaTy]
+ rhs = mkLams [openAlphaTyVar,openBetaTyVar,x] $
+ Note (Coerce openBetaTy openAlphaTy) (Var x)
+
+-- nullAddr# :: Addr#
+-- The reason is is here is because we don't provide
+-- a way to write this literal in Haskell.
+nullAddrId
+ = pcMiscPrelId nullAddrName addrPrimTy info
+ where
+ info = noCafIdInfo `setUnfoldingInfo`
+ mkCompulsoryUnfolding (Lit nullAddrLit)
+
+seqId
+ = pcMiscPrelId seqName ty info
+ where
+ info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
+
+
+ ty = mkForAllTys [alphaTyVar,openBetaTyVar]
+ (mkFunTy alphaTy (mkFunTy openBetaTy openBetaTy))
+ [x,y] = mkTemplateLocals [alphaTy, openBetaTy]
+ rhs = mkLams [alphaTyVar,openBetaTyVar,x,y] (Case (Var x) x [(DEFAULT, [], Var y)])
+
+-- lazy :: forall a?. a? -> a? (i.e. works for unboxed types too)
+-- Used to lazify pseq: pseq a b = a `seq` lazy b
+-- No unfolding: it gets "inlined" by the worker/wrapper pass
+-- Also, no strictness: by being a built-in Id, it overrides all
+-- the info in PrelBase.hi. This is important, because the strictness
+-- analyser will spot it as strict!
+lazyId
+ = pcMiscPrelId lazyIdName ty info
+ where
+ info = noCafIdInfo
+ ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy alphaTy)
+
+lazyIdUnfolding :: CoreExpr -- Used to expand LazyOp after strictness anal
+lazyIdUnfolding = mkLams [openAlphaTyVar,x] (Var x)
+ where
+ [x] = mkTemplateLocals [openAlphaTy]
+\end{code}
+
+@realWorld#@ used to be a magic literal, \tr{void#}. If things get
+nasty as-is, change it back to a literal (@Literal@).
+
+voidArgId is a Local Id used simply as an argument in functions
+where we just want an arg to avoid having a thunk of unlifted type.
+E.g.
+ x = \ void :: State# RealWorld -> (# p, q #)
+
+This comes up in strictness analysis
+
+\begin{code}
+realWorldPrimId -- :: State# RealWorld
+ = pcMiscPrelId realWorldName realWorldStatePrimTy
+ (noCafIdInfo `setUnfoldingInfo` mkOtherCon [])
+ -- The mkOtherCon makes it look that realWorld# is evaluated
+ -- which in turn makes Simplify.interestingArg return True,
+ -- which in turn makes INLINE things applied to realWorld# likely
+ -- to be inlined
+
+voidArgId -- :: State# RealWorld
+ = mkSysLocal FSLIT("void") voidArgIdKey realWorldStatePrimTy
projects / ghc-hetmet.git / blobdiff