X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FbasicTypes%2FMkId.lhs;h=7060c803060a0f74bdad35849aa040cbe8dbe9fa;hb=291f2adda098f7e275db3720ed07e7dc77c821c4;hp=986542bdb3a1a79a64b1d2d6d0fee5add4e226f7;hpb=9414bda057e8ac8422ca5590c8500c7cdee323bb;p=ghc-hetmet.git diff --git a/compiler/basicTypes/MkId.lhs b/compiler/basicTypes/MkId.lhs index 986542b..7060c80 100644 --- a/compiler/basicTypes/MkId.lhs +++ b/compiler/basicTypes/MkId.lhs @@ -33,7 +33,7 @@ module MkId ( -- And some particular Ids; see below for why they are wired in wiredInIds, ghcPrimIds, unsafeCoerceId, realWorldPrimId, voidArgId, nullAddrId, seqId, - lazyId, lazyIdUnfolding, lazyIdKey, + lazyId, lazyIdKey, mkRuntimeErrorApp, mkImpossibleExpr, rEC_CON_ERROR_ID, iRREFUT_PAT_ERROR_ID, rUNTIME_ERROR_ID, @@ -50,7 +50,6 @@ import TysPrim import TysWiredIn import PrelRules import Type -import TypeRep import Coercion import TcType import CoreUtils ( exprType, mkCoerce ) @@ -60,7 +59,6 @@ import TyCon import Class import VarSet import Name -import OccName import PrimOp import ForeignCall import DataCon @@ -70,7 +68,6 @@ import IdInfo import NewDemand import CoreSyn import Unique -import Maybes import PrelNames import BasicTypes hiding ( SuccessFlag(..) ) import Util @@ -86,17 +83,42 @@ import Module %* * %************************************************************************ +Note [Wired-in Ids] +~~~~~~~~~~~~~~~~~~~ +There are several reasons why an Id might appear in the wiredInIds: + +(1) The ghcPrimIds are wired in because they can't be defined in + Haskell at all, although the can be defined in Core. They have + compulsory unfoldings, so they are always inlined and they have + no definition site. Their home module is GHC.Prim, so they + also have a description in primops.txt.pp, where they are called + 'pseudoops'. + +(2) The 'error' function, eRROR_ID, is wired in because we don't yet have + a way to express in an interface file that the result type variable + is 'open'; that is can be unified with an unboxed type + + [The interface file format now carry such information, but there's + no way yet of expressing at the definition site for these + error-reporting functions that they have an 'open' + result type. -- sof 1/99] + +(3) Other error functions (rUNTIME_ERROR_ID) are wired in (a) because + the desugarer generates code that mentiones them directly, and + (b) for the same reason as eRROR_ID + +(4) lazyId is wired in because the wired-in version overrides the + strictness of the version defined in GHC.Base + +In cases (2-4), the function has a definition in a library module, and +can be called; but the wired-in version means that the details are +never read from that module's interface file; instead, the full definition +is right here. + \begin{code} wiredInIds :: [Id] wiredInIds - = [ -- These error-y things are wired in because we don't yet have - -- a way to express in an interface file that the result type variable - -- is 'open'; that is can be unified with an unboxed type - -- - -- [The interface file format now carry such information, but there's - -- no way yet of expressing at the definition site for these - -- error-reporting functions that they have an 'open' - -- result type. -- sof 1/99] + = [ eRROR_ID, -- This one isn't used anywhere else in the compiler -- But we still need it in wiredInIds so that when GHC @@ -879,11 +901,7 @@ nullAddrId = pcMiscPrelId nullAddrName addrPrimTy info mkCompulsoryUnfolding (Lit nullAddrLit) ------------------------------------------------ -seqId :: Id --- 'seq' is very special. See notes with --- See DsUtils.lhs Note [Desugaring seq (1)] and --- Note [Desugaring seq (2)] and --- Fixity is set in LoadIface.ghcPrimIface +seqId :: Id -- See Note [seqId magic] seqId = pcMiscPrelId seqName ty info where info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs @@ -895,29 +913,72 @@ seqId = pcMiscPrelId seqName ty info rhs = mkLams [alphaTyVar,openBetaTyVar,x,y] (Case (Var x) x openBetaTy [(DEFAULT, [], Var y)]) ------------------------------------------------ -lazyId :: Id --- lazy :: forall a?. a? -> a? (i.e. works for unboxed types too) --- Used to lazify pseq: pseq a b = a `seq` lazy b --- --- Also, no strictness: by being a built-in Id, all the info about lazyId comes from here, --- not from GHC.Base.hi. This is important, because the strictness --- analyser will spot it as strict! --- --- Also no unfolding in lazyId: it gets "inlined" by a HACK in the worker/wrapperpass --- (see WorkWrap.wwExpr) --- We could use inline phases to do this, but that would be vulnerable to changes in --- phase numbering....we must inline precisely after strictness analysis. +lazyId :: Id -- See Note [lazyId magic] lazyId = pcMiscPrelId lazyIdName ty info where info = noCafIdInfo ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy alphaTy) - -lazyIdUnfolding :: CoreExpr -- Used to expand 'lazyId' after strictness anal -lazyIdUnfolding = mkLams [openAlphaTyVar,x] (Var x) - where - [x] = mkTemplateLocals [openAlphaTy] \end{code} +Note [seqId magic] +~~~~~~~~~~~~~~~~~~ +'GHC.Prim.seq' is special in several ways. + +a) Its second arg can have an unboxed type + x `seq` (v +# w) + +b) Its fixity is set in LoadIface.ghcPrimIface + +c) It has quite a bit of desugaring magic. + See DsUtils.lhs Note [Desugaring seq (1)] and (2) and (3) + +d) There is some special rule handing: Note [RULES for seq] + +Note [Rules for seq] +~~~~~~~~~~~~~~~~~~~~ +Roman found situations where he had + case (f n) of _ -> e +where he knew that f (which was strict in n) would terminate if n did. +Notice that the result of (f n) is discarded. So it makes sense to +transform to + case n of _ -> e + +Rather than attempt some general analysis to support this, I've added +enough support that you can do this using a rewrite rule: + + RULE "f/seq" forall n. seq (f n) e = seq n e + +You write that rule. When GHC sees a case expression that discards +its result, it mentally transforms it to a call to 'seq' and looks for +a RULE. (This is done in Simplify.rebuildCase.) As usual, the +correctness of the rule is up to you. + +To make this work, we need to be careful that the magical desugaring +done in Note [seqId magic] item (c) is *not* done on the LHS of a rule. +Or rather, we arrange to un-do it, in DsBinds.decomposeRuleLhs. + + +Note [lazyId magic] +~~~~~~~~~~~~~~~~~~~ + lazy :: forall a?. a? -> a? (i.e. works for unboxed types too) + +Used to lazify pseq: pseq a b = a `seq` lazy b + +Also, no strictness: by being a built-in Id, all the info about lazyId comes from here, +not from GHC.Base.hi. This is important, because the strictness +analyser will spot it as strict! + +Also no unfolding in lazyId: it gets "inlined" by a HACK in CorePrep. +It's very important to do this inlining *after* unfoldings are exposed +in the interface file. Otherwise, the unfolding for (say) pseq in the +interface file will not mention 'lazy', so if we inline 'pseq' we'll totally +miss the very thing that 'lazy' was there for in the first place. +See Trac #3259 for a real world example. + +lazyId is defined in GHC.Base, so we don't *have* to inline it. If it +appears un-applied, we'll end up just calling it. + +------------------------------------------------------------- @realWorld#@ used to be a magic literal, \tr{void#}. If things get nasty as-is, change it back to a literal (@Literal@).