%
-% (c) The AQUA Project, Glasgow University, 1993-1996
+% (c) The AQUA Project, Glasgow University, 1993-1998
%
\section[Simplify]{The main module of the simplifier}
\begin{code}
-module Simplify ( simplTopBinds, simplExpr, simplBind ) where
+module Simplify ( simplTopBinds, simplExpr ) where
#include "HsVersions.h"
-import BinderInfo
-import CmdLineOpts ( SimplifierSwitch(..) )
-import ConFold ( completePrim )
-import CoreUnfold ( Unfolding, mkFormSummary,
- exprIsTrivial, whnfOrBottom, inlineUnconditionally,
- FormSummary(..)
+import CmdLineOpts ( dopt, DynFlag(Opt_D_dump_inlinings),
+ SimplifierSwitch(..)
)
-import CostCentre ( isSccCountCostCentre, cmpCostCentre, costsAreSubsumed, useCurrentCostCentre )
+import SimplMonad
+import SimplUtils ( mkCase, mkLam, newId, prepareAlts,
+ simplBinder, simplBinders, simplLamBndrs, simplRecBndrs, simplLetBndr,
+ SimplCont(..), DupFlag(..), LetRhsFlag(..),
+ mkStop, mkBoringStop, pushContArgs,
+ contResultType, countArgs, contIsDupable, contIsRhsOrArg,
+ getContArgs, interestingCallContext, interestingArg, isStrictType
+ )
+import Var ( mustHaveLocalBinding )
+import VarEnv
+import Id ( Id, idType, idInfo, idArity, isDataConId,
+ setIdUnfolding, isDeadBinder,
+ idNewDemandInfo, setIdInfo,
+ setIdOccInfo, zapLamIdInfo, setOneShotLambda,
+ )
+import OccName ( encodeFS )
+import IdInfo ( OccInfo(..), isLoopBreaker,
+ setArityInfo,
+ setUnfoldingInfo,
+ occInfo
+ )
+import NewDemand ( isStrictDmd )
+import DataCon ( dataConNumInstArgs, dataConRepStrictness )
import CoreSyn
-import CoreUtils ( coreExprType, nonErrorRHSs, maybeErrorApp,
- unTagBinders, squashableDictishCcExpr
+import PprCore ( pprParendExpr, pprCoreExpr )
+import CoreUnfold ( mkOtherCon, mkUnfolding, callSiteInline )
+import CoreUtils ( exprIsDupable, exprIsTrivial, needsCaseBinding,
+ exprIsConApp_maybe, mkPiTypes, findAlt,
+ exprType, exprIsValue,
+ exprOkForSpeculation, exprArity,
+ mkCoerce, mkCoerce2, mkSCC, mkInlineMe, mkAltExpr, applyTypeToArg
)
-import Id ( idType, idMustBeINLINEd, idWantsToBeINLINEd, idMustNotBeINLINEd,
- addIdArity, getIdArity,
- getIdDemandInfo, addIdDemandInfo
+import Rules ( lookupRule )
+import BasicTypes ( isMarkedStrict )
+import CostCentre ( currentCCS )
+import Type ( isUnLiftedType, seqType, tyConAppArgs, funArgTy,
+ splitFunTy_maybe, splitFunTy, eqType
)
-import Name ( isExported, isLocallyDefined )
-import IdInfo ( willBeDemanded, noDemandInfo, DemandInfo, ArityInfo(..),
- atLeastArity, unknownArity )
-import Literal ( isNoRepLit )
-import Maybes ( maybeToBool )
-import PrimOp ( primOpOkForSpeculation, PrimOp(..) )
-import SimplCase ( simplCase, bindLargeRhs )
-import SimplEnv
-import SimplMonad
-import SimplVar ( completeVar, simplBinder, simplBinders, simplTyBinder, simplTyBinders )
-import SimplUtils
-import Type ( mkTyVarTy, mkTyVarTys, mkAppTy, applyTy, applyTys,
- mkFunTys, splitAlgTyConApp_maybe,
- splitFunTys, splitFunTy_maybe, isUnpointedType
+import Subst ( mkSubst, substTy, substExpr,
+ isInScope, lookupIdSubst, simplIdInfo
)
import TysPrim ( realWorldStatePrimTy )
-import Util ( Eager, appEager, returnEager, runEager, mapEager,
- isSingleton, zipEqual, zipWithEqual, mapAndUnzip
+import PrelInfo ( realWorldPrimId )
+import BasicTypes ( TopLevelFlag(..), isTopLevel,
+ RecFlag(..), isNonRec
)
-import Outputable
+import OrdList
+import Maybe ( Maybe )
+import Outputable
+import Util ( notNull )
\end{code}
-The controlling flags, and what they do
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-passes:
-------
--fsimplify = run the simplifier
--ffloat-inwards = runs the float lets inwards pass
--ffloat = runs the full laziness pass
- (ToDo: rename to -ffull-laziness)
--fupdate-analysis = runs update analyser
--fstrictness = runs strictness analyser
--fsaturate-apps = saturates applications (eta expansion)
-
-options:
--------
--ffloat-past-lambda = OK to do full laziness.
- (ToDo: remove, as the full laziness pass is
- useless without this flag, therefore
- it is unnecessary. Just -ffull-laziness
- should be kept.)
-
--ffloat-lets-ok = OK to float lets out of lets if the enclosing
- let is strict or if the floating will expose
- a WHNF [simplifier].
-
--ffloat-primops-ok = OK to float out of lets cases whose scrutinee
- is a primop that cannot fail [simplifier].
-
--fcode-duplication-ok = allows the previous option to work on cases with
- multiple branches [simplifier].
-
--flet-to-case = does let-to-case transformation [simplifier].
-
--fcase-of-case = does case of case transformation [simplifier].
-
--fpedantic-bottoms = does not allow:
- case x of y -> e ===> e[x/y]
- (which may turn bottom into non-bottom)
-
-
- NOTES ON INLINING
- ~~~~~~~~~~~~~~~~~
-
-Inlining is one of the delicate aspects of the simplifier. By
-``inlining'' we mean replacing an occurrence of a variable ``x'' by
-the RHS of x's definition. Thus
-
- let x = e in ...x... ===> let x = e in ...e...
-
-We have two mechanisms for inlining:
-
-1. Unconditional. The occurrence analyser has pinned an (OneOcc
-FunOcc NoDupDanger NotInsideSCC n) flag on the variable, saying ``it's
-certainly safe to inline this variable, and to drop its binding''.
-(...Umm... if n <= 1; if n > 1, it is still safe, provided you are
-happy to be duplicating code...) When it encounters such a beast, the
-simplifer binds the variable to its RHS (in the id_env) and continues.
-It doesn't even look at the RHS at that stage. It also drops the
-binding altogether.
-
-2. Conditional. In all other situations, the simplifer simplifies
-the RHS anyway, and keeps the new binding. It also binds the new
-(cloned) variable to a ``suitable'' Unfolding in the UnfoldEnv.
-
-Here, ``suitable'' might mean NoUnfolding (if the occurrence
-info is ManyOcc and the RHS is not a manifest HNF, or UnfoldAlways (if
-the variable has an INLINE pragma on it). The idea is that anything
-in the UnfoldEnv is safe to use, but also has an enclosing binding if
-you decide not to use it.
-
-Head normal forms
-~~~~~~~~~~~~~~~~~
-We *never* put a non-HNF unfolding in the UnfoldEnv except in the
-INLINE-pragma case.
-
-At one time I thought it would be OK to put non-HNF unfoldings in for
-variables which occur only once [if they got inlined at that
-occurrence the RHS of the binding would become dead, so no duplication
-would occur]. But consider:
-@
- let x = <expensive>
- f = \y -> ...y...y...y...
- in f x
-@
-Now, it seems that @x@ appears only once, but even so it is NOT safe
-to put @x@ in the UnfoldEnv, because @f@ will be inlined, and will
-duplicate the references to @x@.
-
-Because of this, the "unconditional-inline" mechanism above is the
-only way in which non-HNFs can get inlined.
-
-INLINE pragmas
-~~~~~~~~~~~~~~
-When a variable has an INLINE pragma on it --- which includes wrappers
-produced by the strictness analyser --- we treat it rather carefully.
+The guts of the simplifier is in this module, but the driver loop for
+the simplifier is in SimplCore.lhs.
-For a start, we are careful not to substitute into its RHS, because
-that might make it BIG, and the user said "inline exactly this", not
-"inline whatever you get after inlining other stuff inside me". For
-example
- let f = BIG
- in {-# INLINE y #-} y = f 3
- in ...y...y...
+-----------------------------------------
+ *** IMPORTANT NOTE ***
+-----------------------------------------
+The simplifier used to guarantee that the output had no shadowing, but
+it does not do so any more. (Actually, it never did!) The reason is
+documented with simplifyArgs.
-Here we don't want to substitute BIG for the (single) occurrence of f,
-because then we'd duplicate BIG when we inline'd y. (Exception:
-things in the UnfoldEnv with UnfoldAlways flags, which originated in
-other INLINE pragmas.)
-So, we clean out the UnfoldEnv of all SimpleUnfolding inlinings before
-going into such an RHS.
+-----------------------------------------
+ *** IMPORTANT NOTE ***
+-----------------------------------------
+Many parts of the simplifier return a bunch of "floats" as well as an
+expression. This is wrapped as a datatype SimplUtils.FloatsWith.
-What about imports? They don't really matter much because we only
-inline relatively small things via imports.
+All "floats" are let-binds, not case-binds, but some non-rec lets may
+be unlifted (with RHS ok-for-speculation).
-We augment the the UnfoldEnv with UnfoldAlways guidance if there's an
-INLINE pragma. We also do this for the RHSs of recursive decls,
-before looking at the recursive decls. That way we achieve the effect
-of inlining a wrapper in the body of its worker, in the case of a
-mutually-recursive worker/wrapper split.
-%************************************************************************
-%* *
-\subsection[Simplify-simplExpr]{The main function: simplExpr}
-%* *
-%************************************************************************
+-----------------------------------------
+ ORGANISATION OF FUNCTIONS
+-----------------------------------------
+simplTopBinds
+ - simplify all top-level binders
+ - for NonRec, call simplRecOrTopPair
+ - for Rec, call simplRecBind
-At the top level things are a little different.
+
+ ------------------------------
+simplExpr (applied lambda) ==> simplNonRecBind
+simplExpr (Let (NonRec ...) ..) ==> simplNonRecBind
+simplExpr (Let (Rec ...) ..) ==> simplify binders; simplRecBind
+
+ ------------------------------
+simplRecBind [binders already simplfied]
+ - use simplRecOrTopPair on each pair in turn
+
+simplRecOrTopPair [binder already simplified]
+ Used for: recursive bindings (top level and nested)
+ top-level non-recursive bindings
+ Returns:
+ - check for PreInlineUnconditionally
+ - simplLazyBind
+
+simplNonRecBind
+ Used for: non-top-level non-recursive bindings
+ beta reductions (which amount to the same thing)
+ Because it can deal with strict arts, it takes a
+ "thing-inside" and returns an expression
+
+ - check for PreInlineUnconditionally
+ - simplify binder, including its IdInfo
+ - if strict binding
+ simplStrictArg
+ mkAtomicArgs
+ completeNonRecX
+ else
+ simplLazyBind
+ addFloats
+
+simplNonRecX: [given a *simplified* RHS, but an *unsimplified* binder]
+ Used for: binding case-binder and constr args in a known-constructor case
+ - check for PreInLineUnconditionally
+ - simplify binder
+ - completeNonRecX
+
+ ------------------------------
+simplLazyBind: [binder already simplified, RHS not]
+ Used for: recursive bindings (top level and nested)
+ top-level non-recursive bindings
+ non-top-level, but *lazy* non-recursive bindings
+ [must not be strict or unboxed]
+ Returns floats + an augmented environment, not an expression
+ - substituteIdInfo and add result to in-scope
+ [so that rules are available in rec rhs]
+ - simplify rhs
+ - mkAtomicArgs
+ - float if exposes constructor or PAP
+ - completeLazyBind
+
+
+completeNonRecX: [binder and rhs both simplified]
+ - if the the thing needs case binding (unlifted and not ok-for-spec)
+ build a Case
+ else
+ completeLazyBind
+ addFloats
+
+completeLazyBind: [given a simplified RHS]
+ [used for both rec and non-rec bindings, top level and not]
+ - try PostInlineUnconditionally
+ - add unfolding [this is the only place we add an unfolding]
+ - add arity
+
+
+
+Right hand sides and arguments
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+In many ways we want to treat
+ (a) the right hand side of a let(rec), and
+ (b) a function argument
+in the same way. But not always! In particular, we would
+like to leave these arguments exactly as they are, so they
+will match a RULE more easily.
+
+ f (g x, h x)
+ g (+ x)
- * No cloning (not allowed for exported Ids, unnecessary for the others)
- * Floating is done a bit differently (no case floating; check for leaks; handle letrec)
+It's harder to make the rule match if we ANF-ise the constructor,
+or eta-expand the PAP:
-\begin{code}
-simplTopBinds :: SimplEnv -> [InBinding] -> SmplM [OutBinding]
+ f (let { a = g x; b = h x } in (a,b))
+ g (\y. + x y)
--- Dead code is now discarded by the occurrence analyser,
+On the other hand if we see the let-defns
-simplTopBinds env binds
- = mapSmpl (floatBind env True) binds `thenSmpl` \ binds_s ->
- simpl_top_binds env (concat binds_s)
- where
- simpl_top_binds env [] = returnSmpl []
-
- simpl_top_binds env (NonRec binder@(in_id,occ_info) rhs : binds)
- = --- No cloning necessary at top level
- simplBinder env binder `thenSmpl` \ (env1, out_id) ->
- simplRhsExpr env binder rhs out_id `thenSmpl` \ (rhs',arity) ->
- completeNonRec env1 binder (out_id `withArity` arity) rhs' `thenSmpl` \ (new_env, binds1') ->
- simpl_top_binds new_env binds `thenSmpl` \ binds2' ->
- returnSmpl (binds1' ++ binds2')
-
- simpl_top_binds env (Rec pairs : binds)
- = -- No cloning necessary at top level, but we nevertheless
- -- add the Ids to the environment. This makes sure that
- -- info carried on the Id (such as arity info) gets propagated
- -- to occurrences.
- --
- -- This may seem optional, but I found an occasion when it Really matters.
- -- Consider foo{n} = ...foo...
- -- baz* = foo
- --
- -- where baz* is exported and foo isn't. Then when we do "indirection-shorting"
- -- in tidyCore, we need the {no-inline} pragma from foo to attached to the final
- -- thing: baz*{n} = ...baz...
- --
- -- Sure we could have made the indirection-shorting a bit cleverer, but
- -- propagating pragma info is a Good Idea anyway.
- simplBinders env (map fst pairs) `thenSmpl` \ (env1, out_ids) ->
- simplRecursiveGroup env1 out_ids pairs `thenSmpl` \ (bind', new_env) ->
- simpl_top_binds new_env binds `thenSmpl` \ binds' ->
- returnSmpl (Rec bind' : binds')
-\end{code}
+ p = (g x, h x)
+ q = + x
-%************************************************************************
-%* *
-\subsection[Simplify-simplExpr]{The main function: simplExpr}
-%* *
-%************************************************************************
+then we *do* want to ANF-ise and eta-expand, so that p and q
+can be safely inlined.
+Even floating lets out is a bit dubious. For let RHS's we float lets
+out if that exposes a value, so that the value can be inlined more vigorously.
+For example
-\begin{code}
-simplExpr :: SimplEnv
- -> InExpr -> [OutArg]
- -> OutType -- Type of (e args); i.e. type of overall result
- -> SmplM OutExpr
-\end{code}
+ r = let x = e in (x,x)
-The expression returned has the same meaning as the input expression
-applied to the specified arguments.
+Here, if we float the let out we'll expose a nice constructor. We did experiments
+that showed this to be a generally good thing. But it was a bad thing to float
+lets out unconditionally, because that meant they got allocated more often.
+For function arguments, there's less reason to expose a constructor (it won't
+get inlined). Just possibly it might make a rule match, but I'm pretty skeptical.
+So for the moment we don't float lets out of function arguments either.
-Variables
-~~~~~~~~~
-Check if there's a macro-expansion, and if so rattle on. Otherwise do
-the more sophisticated stuff.
-\begin{code}
-simplExpr env (Var var) args result_ty
- = case lookupIdSubst env var of
-
- Just (SubstExpr ty_subst id_subst expr)
- -> simplExpr (setSubstEnvs env ty_subst id_subst) expr args result_ty
+Eta expansion
+~~~~~~~~~~~~~~
+For eta expansion, we want to catch things like
- Just (SubstLit lit) -- A boring old literal
- -> ASSERT( null args )
- returnSmpl (Lit lit)
+ case e of (a,b) -> \x -> case a of (p,q) -> \y -> r
- Just (SubstVar var') -- More interesting! An id!
- -> completeVar env var' args result_ty
+If the \x was on the RHS of a let, we'd eta expand to bring the two
+lambdas together. And in general that's a good thing to do. Perhaps
+we should eta expand wherever we find a (value) lambda? Then the eta
+expansion at a let RHS can concentrate solely on the PAP case.
- Nothing -- Not in the substitution; hand off to completeVar
- -> completeVar env var args result_ty
-\end{code}
-Literals
-~~~~~~~~
+%************************************************************************
+%* *
+\subsection{Bindings}
+%* *
+%************************************************************************
\begin{code}
-simplExpr env (Lit l) [] result_ty = returnSmpl (Lit l)
-#ifdef DEBUG
-simplExpr env (Lit l) _ _ = panic "simplExpr:Lit with argument"
-#endif
-\end{code}
+simplTopBinds :: SimplEnv -> [InBind] -> SimplM [OutBind]
-Primitive applications are simple.
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-NB: Prim expects an empty argument list! (Because it should be
-saturated and not higher-order. ADR)
-
-\begin{code}
-simplExpr env (Prim op prim_args) args result_ty
- = ASSERT (null args)
- mapEager (simplArg env) prim_args `appEager` \ prim_args' ->
- simpl_op op `appEager` \ op' ->
- completePrim env op' prim_args'
+simplTopBinds env binds
+ = -- Put all the top-level binders into scope at the start
+ -- so that if a transformation rule has unexpectedly brought
+ -- anything into scope, then we don't get a complaint about that.
+ -- It's rather as if the top-level binders were imported.
+ simplRecBndrs env (bindersOfBinds binds) `thenSmpl` \ (env, bndrs') ->
+ simpl_binds env binds bndrs' `thenSmpl` \ (floats, _) ->
+ freeTick SimplifierDone `thenSmpl_`
+ returnSmpl (floatBinds floats)
where
- -- PrimOps just need any types in them renamed.
-
- simpl_op (CCallOp label is_asm may_gc arg_tys result_ty)
- = mapEager (simplTy env) arg_tys `appEager` \ arg_tys' ->
- simplTy env result_ty `appEager` \ result_ty' ->
- returnEager (CCallOp label is_asm may_gc arg_tys' result_ty')
-
- simpl_op other_op = returnEager other_op
-\end{code}
-
-Constructor applications
-~~~~~~~~~~~~~~~~~~~~~~~~
-Nothing to try here. We only reuse constructors when they appear as the
-rhs of a let binding (see completeLetBinding).
+ -- We need to track the zapped top-level binders, because
+ -- they should have their fragile IdInfo zapped (notably occurrence info)
+ -- That's why we run down binds and bndrs' simultaneously.
+ simpl_binds :: SimplEnv -> [InBind] -> [OutId] -> SimplM (FloatsWith ())
+ simpl_binds env [] bs = ASSERT( null bs ) returnSmpl (emptyFloats env, ())
+ simpl_binds env (bind:binds) bs = simpl_bind env bind bs `thenSmpl` \ (floats,env) ->
+ addFloats env floats $ \env ->
+ simpl_binds env binds (drop_bs bind bs)
+
+ drop_bs (NonRec _ _) (_ : bs) = bs
+ drop_bs (Rec prs) bs = drop (length prs) bs
+
+ simpl_bind env bind bs
+ = getDOptsSmpl `thenSmpl` \ dflags ->
+ if dopt Opt_D_dump_inlinings dflags then
+ pprTrace "SimplBind" (ppr (bindersOf bind)) $ simpl_bind1 env bind bs
+ else
+ simpl_bind1 env bind bs
-\begin{code}
-simplExpr env (Con con con_args) args result_ty
- = ASSERT( null args )
- mapEager (simplArg env) con_args `appEager` \ con_args' ->
- returnSmpl (Con con con_args')
+ simpl_bind1 env (NonRec b r) (b':_) = simplRecOrTopPair env TopLevel b b' r
+ simpl_bind1 env (Rec pairs) bs' = simplRecBind env TopLevel pairs bs'
\end{code}
-Applications are easy too:
-~~~~~~~~~~~~~~~~~~~~~~~~~~
-Just stuff 'em in the arg stack
+%************************************************************************
+%* *
+\subsection{simplNonRec}
+%* *
+%************************************************************************
-\begin{code}
-simplExpr env (App fun arg) args result_ty
- = simplArg env arg `appEager` \ arg' ->
- simplExpr env fun (arg' : args) result_ty
-\end{code}
+simplNonRecBind is used for
+ * non-top-level non-recursive lets in expressions
+ * beta reduction
-Type lambdas
-~~~~~~~~~~~~
+It takes
+ * An unsimplified (binder, rhs) pair
+ * The env for the RHS. It may not be the same as the
+ current env because the bind might occur via (\x.E) arg
-First the case when it's applied to an argument.
+It uses the CPS form because the binding might be strict, in which
+case we might discard the continuation:
+ let x* = error "foo" in (...x...)
-\begin{code}
-simplExpr env (Lam (TyBinder tyvar) body) (TyArg ty : args) result_ty
- = tick TyBetaReduction `thenSmpl_`
- simplExpr (bindTyVar env tyvar ty) body args result_ty
-\end{code}
+It needs to turn unlifted bindings into a @case@. They can arise
+from, say: (\x -> e) (4# + 3#)
\begin{code}
-simplExpr env tylam@(Lam (TyBinder tyvar) body) [] result_ty
- = simplTyBinder env tyvar `thenSmpl` \ (new_env, tyvar') ->
- let
- new_result_ty = applyTy result_ty (mkTyVarTy tyvar')
- in
- simplExpr new_env body [] new_result_ty `thenSmpl` \ body' ->
- returnSmpl (Lam (TyBinder tyvar') body')
-
+simplNonRecBind :: SimplEnv
+ -> InId -- Binder
+ -> InExpr -> SimplEnv -- Arg, with its subst-env
+ -> OutType -- Type of thing computed by the context
+ -> (SimplEnv -> SimplM FloatsWithExpr) -- The body
+ -> SimplM FloatsWithExpr
#ifdef DEBUG
-simplExpr env (Lam (TyBinder _) _) (_ : _) result_ty
- = panic "simplExpr:TyLam with non-TyArg"
+simplNonRecBind env bndr rhs rhs_se cont_ty thing_inside
+ | isTyVar bndr
+ = pprPanic "simplNonRecBind" (ppr bndr <+> ppr rhs)
#endif
-\end{code}
+simplNonRecBind env bndr rhs rhs_se cont_ty thing_inside
+ | preInlineUnconditionally env NotTopLevel bndr
+ = tick (PreInlineUnconditionally bndr) `thenSmpl_`
+ thing_inside (extendSubst env bndr (ContEx (getSubstEnv rhs_se) rhs))
-Ordinary lambdas
-~~~~~~~~~~~~~~~~
-There's a complication with lambdas that aren't saturated.
-Suppose we have:
-
- (\x. \y. ...x...)
+ | isStrictDmd (idNewDemandInfo bndr) || isStrictType (idType bndr) -- A strict let
+ = -- Don't use simplBinder because that doesn't keep
+ -- fragile occurrence info in the substitution
+ simplLetBndr env bndr `thenSmpl` \ (env, bndr') ->
+ let
+ -- simplLetBndr doesn't deal with the IdInfo, so we must
+ -- do so here (c.f. simplLazyBind)
+ bndr'' = bndr' `setIdInfo` simplIdInfo (getSubst env) (idInfo bndr)
+ env1 = modifyInScope env bndr'' bndr''
+ in
+ simplStrictArg AnRhs env1 rhs rhs_se (idType bndr') cont_ty $ \ env rhs1 ->
+
+ -- Now complete the binding and simplify the body
+ completeNonRecX env True {- strict -} bndr bndr'' rhs1 thing_inside
+
+ | otherwise -- Normal, lazy case
+ = -- Don't use simplBinder because that doesn't keep
+ -- fragile occurrence info in the substitution
+ simplLetBndr env bndr `thenSmpl` \ (env, bndr') ->
+ simplLazyBind env NotTopLevel NonRecursive
+ bndr bndr' rhs rhs_se `thenSmpl` \ (floats, env) ->
+ addFloats env floats thing_inside
+\end{code}
-If we did nothing, x is used inside the \y, so would be marked
-as dangerous to dup. But in the common case where the abstraction
-is applied to two arguments this is over-pessimistic.
-So instead we don't take account of the \y when dealing with x's usage;
-instead, the simplifier is careful when partially applying lambdas.
+A specialised variant of simplNonRec used when the RHS is already simplified, notably
+in knownCon. It uses case-binding where necessary.
\begin{code}
-simplExpr env expr@(Lam (ValBinder binder) body) orig_args result_ty
- = go 0 env expr orig_args
- where
- go n env (Lam (ValBinder binder) body) (val_arg : args)
- | isValArg val_arg -- The lambda has an argument
- = tick BetaReduction `thenSmpl_`
- go (n+1) (bindIdToAtom env binder val_arg) body args
-
- go n env expr@(Lam (ValBinder binder) body) args
- -- The lambda is un-saturated, so we must zap the occurrence info
- -- on the arguments we've already beta-reduced into the body of the lambda
- = ASSERT( null args ) -- Value lambda must match value argument!
- let
- new_env = markDangerousOccs env orig_args
- in
- simplValLam new_env expr 0 {- Guaranteed applied to at least 0 args! -} result_ty
- `thenSmpl` \ (expr', arity) ->
- returnSmpl expr'
-
- go n env non_val_lam_expr args -- The lambda had enough arguments
- = simplExpr env non_val_lam_expr args result_ty
+simplNonRecX :: SimplEnv
+ -> InId -- Old binder
+ -> OutExpr -- Simplified RHS
+ -> (SimplEnv -> SimplM FloatsWithExpr)
+ -> SimplM FloatsWithExpr
+
+simplNonRecX env bndr new_rhs thing_inside
+ | needsCaseBinding (idType bndr) new_rhs
+ -- Make this test *before* the preInlineUnconditionally
+ -- Consider case I# (quotInt# x y) of
+ -- I# v -> let w = J# v in ...
+ -- If we gaily inline (quotInt# x y) for v, we end up building an
+ -- extra thunk:
+ -- let w = J# (quotInt# x y) in ...
+ -- because quotInt# can fail.
+ = simplBinder env bndr `thenSmpl` \ (env, bndr') ->
+ thing_inside env `thenSmpl` \ (floats, body) ->
+ returnSmpl (emptyFloats env, Case new_rhs bndr' [(DEFAULT, [], wrapFloats floats body)])
+
+ | preInlineUnconditionally env NotTopLevel bndr
+ -- This happens; for example, the case_bndr during case of
+ -- known constructor: case (a,b) of x { (p,q) -> ... }
+ -- Here x isn't mentioned in the RHS, so we don't want to
+ -- create the (dead) let-binding let x = (a,b) in ...
+ --
+ -- Similarly, single occurrences can be inlined vigourously
+ -- e.g. case (f x, g y) of (a,b) -> ....
+ -- If a,b occur once we can avoid constructing the let binding for them.
+ = thing_inside (extendSubst env bndr (ContEx emptySubstEnv new_rhs))
+
+ | otherwise
+ = simplBinder env bndr `thenSmpl` \ (env, bndr') ->
+ completeNonRecX env False {- Non-strict; pessimistic -}
+ bndr bndr' new_rhs thing_inside
+
+completeNonRecX env is_strict old_bndr new_bndr new_rhs thing_inside
+ = mkAtomicArgs is_strict
+ True {- OK to float unlifted -}
+ new_rhs `thenSmpl` \ (aux_binds, rhs2) ->
+
+ -- Make the arguments atomic if necessary,
+ -- adding suitable bindings
+ addAtomicBindsE env (fromOL aux_binds) $ \ env ->
+ completeLazyBind env NotTopLevel
+ old_bndr new_bndr rhs2 `thenSmpl` \ (floats, env) ->
+ addFloats env floats thing_inside
\end{code}
-Let expressions
-~~~~~~~~~~~~~~~
+%************************************************************************
+%* *
+\subsection{Lazy bindings}
+%* *
+%************************************************************************
+
+simplRecBind is used for
+ * recursive bindings only
\begin{code}
-simplExpr env (Let bind body) args result_ty
- = simplBind env bind (\env -> simplExpr env body args result_ty) result_ty
+simplRecBind :: SimplEnv -> TopLevelFlag
+ -> [(InId, InExpr)] -> [OutId]
+ -> SimplM (FloatsWith SimplEnv)
+simplRecBind env top_lvl pairs bndrs'
+ = go env pairs bndrs' `thenSmpl` \ (floats, env) ->
+ returnSmpl (flattenFloats floats, env)
+ where
+ go env [] _ = returnSmpl (emptyFloats env, env)
+
+ go env ((bndr, rhs) : pairs) (bndr' : bndrs')
+ = simplRecOrTopPair env top_lvl bndr bndr' rhs `thenSmpl` \ (floats, env) ->
+ addFloats env floats (\env -> go env pairs bndrs')
\end{code}
-Case expressions
-~~~~~~~~~~~~~~~~
-\begin{code}
-simplExpr env expr@(Case scrut alts) args result_ty
- = simplCase env scrut alts (\env rhs -> simplExpr env rhs args result_ty) result_ty
-\end{code}
+simplRecOrTopPair is used for
+ * recursive bindings (whether top level or not)
+ * top-level non-recursive bindings
+It assumes the binder has already been simplified, but not its IdInfo.
-Coercions
-~~~~~~~~~
\begin{code}
-simplExpr env (Coerce coercion ty body) args result_ty
- = simplCoerce env coercion ty body args result_ty
-\end{code}
+simplRecOrTopPair :: SimplEnv
+ -> TopLevelFlag
+ -> InId -> OutId -- Binder, both pre-and post simpl
+ -> InExpr -- The RHS and its environment
+ -> SimplM (FloatsWith SimplEnv)
+simplRecOrTopPair env top_lvl bndr bndr' rhs
+ | preInlineUnconditionally env top_lvl bndr -- Check for unconditional inline
+ = tick (PreInlineUnconditionally bndr) `thenSmpl_`
+ returnSmpl (emptyFloats env, extendSubst env bndr (ContEx (getSubstEnv env) rhs))
-Set-cost-centre
-~~~~~~~~~~~~~~~
+ | otherwise
+ = simplLazyBind env top_lvl Recursive bndr bndr' rhs env
+ -- May not actually be recursive, but it doesn't matter
+\end{code}
-1) Eliminating nested sccs ...
-We must be careful to maintain the scc counts ...
-\begin{code}
-simplExpr env (SCC cc1 (SCC cc2 expr)) args result_ty
- | not (isSccCountCostCentre cc2) && case cmpCostCentre cc1 cc2 of { EQ -> True; _ -> False }
- -- eliminate inner scc if no call counts and same cc as outer
- = simplExpr env (SCC cc1 expr) args result_ty
-
- | not (isSccCountCostCentre cc2) && not (isSccCountCostCentre cc1)
- -- eliminate outer scc if no call counts associated with either ccs
- = simplExpr env (SCC cc2 expr) args result_ty
-\end{code}
+simplLazyBind is used for
+ * recursive bindings (whether top level or not)
+ * top-level non-recursive bindings
+ * non-top-level *lazy* non-recursive bindings
-2) Moving sccs inside lambdas ...
-
-\begin{code}
-simplExpr env (SCC cc (Lam binder@(ValBinder _) body)) args result_ty
- | not (isSccCountCostCentre cc)
- -- move scc inside lambda only if no call counts
- = simplExpr env (Lam binder (SCC cc body)) args result_ty
-
-simplExpr env (SCC cc (Lam binder body)) args result_ty
- -- always ok to move scc inside type/usage lambda
- = simplExpr env (Lam binder (SCC cc body)) args result_ty
-\end{code}
+[Thus it deals with the lazy cases from simplNonRecBind, and all cases
+from SimplRecOrTopBind]
-3) Eliminating dict sccs ...
+Nota bene:
+ 1. It assumes that the binder is *already* simplified,
+ and is in scope, but not its IdInfo
-\begin{code}
-simplExpr env (SCC cc expr) args result_ty
- | squashableDictishCcExpr cc expr
- -- eliminate dict cc if trivial dict expression
- = simplExpr env expr args result_ty
-\end{code}
+ 2. It assumes that the binder type is lifted.
-4) Moving arguments inside the body of an scc ...
-This moves the cost of doing the application inside the scc
-(which may include the cost of extracting methods etc)
+ 3. It does not check for pre-inline-unconditionallly;
+ that should have been done already.
\begin{code}
-simplExpr env (SCC cost_centre body) args result_ty
- = let
- new_env = setEnclosingCC env cost_centre
+simplLazyBind :: SimplEnv
+ -> TopLevelFlag -> RecFlag
+ -> InId -> OutId -- Binder, both pre-and post simpl
+ -> InExpr -> SimplEnv -- The RHS and its environment
+ -> SimplM (FloatsWith SimplEnv)
+
+simplLazyBind env top_lvl is_rec bndr bndr' rhs rhs_se
+ = -- Substitute IdInfo on binder, in the light of earlier
+ -- substitutions in this very letrec, and extend the
+ -- in-scope env, so that the IdInfo for this binder extends
+ -- over the RHS for the binder itself.
+ --
+ -- This is important. Manuel found cases where he really, really
+ -- wanted a RULE for a recursive function to apply in that function's
+ -- own right-hand side.
+ --
+ -- NB: does no harm for non-recursive bindings
+ let
+ bndr'' = bndr' `setIdInfo` simplIdInfo (getSubst env) (idInfo bndr)
+ env1 = modifyInScope env bndr'' bndr''
+ rhs_env = setInScope rhs_se env1
+ is_top_level = isTopLevel top_lvl
+ ok_float_unlifted = not is_top_level && isNonRec is_rec
+ rhs_cont = mkStop (idType bndr') AnRhs
in
- simplExpr new_env body args result_ty `thenSmpl` \ body' ->
- returnSmpl (SCC cost_centre body')
+ -- Simplify the RHS; note the mkStop, which tells
+ -- the simplifier that this is the RHS of a let.
+ simplExprF rhs_env rhs rhs_cont `thenSmpl` \ (floats, rhs1) ->
+
+ -- If any of the floats can't be floated, give up now
+ -- (The allLifted predicate says True for empty floats.)
+ if (not ok_float_unlifted && not (allLifted floats)) then
+ completeLazyBind env1 top_lvl bndr bndr''
+ (wrapFloats floats rhs1)
+ else
+
+ -- ANF-ise a constructor or PAP rhs
+ mkAtomicArgs False {- Not strict -}
+ ok_float_unlifted rhs1 `thenSmpl` \ (aux_binds, rhs2) ->
+
+ -- If the result is a PAP, float the floats out, else wrap them
+ -- By this time it's already been ANF-ised (if necessary)
+ if isEmptyFloats floats && isNilOL aux_binds then -- Shortcut a common case
+ completeLazyBind env1 top_lvl bndr bndr'' rhs2
+
+ -- We use exprIsTrivial here because we want to reveal lone variables.
+ -- E.g. let { x = letrec { y = E } in y } in ...
+ -- Here we definitely want to float the y=E defn.
+ -- exprIsValue definitely isn't right for that.
+ --
+ -- BUT we can't use "exprIsCheap", because that causes a strictness bug.
+ -- x = let y* = E in case (scc y) of { T -> F; F -> T}
+ -- The case expression is 'cheap', but it's wrong to transform to
+ -- y* = E; x = case (scc y) of {...}
+ -- Either we must be careful not to float demanded non-values, or
+ -- we must use exprIsValue for the test, which ensures that the
+ -- thing is non-strict. I think. The WARN below tests for this.
+ else if is_top_level || exprIsTrivial rhs2 || exprIsValue rhs2 then
+
+ -- There's a subtlety here. There may be a binding (x* = e) in the
+ -- floats, where the '*' means 'will be demanded'. So is it safe
+ -- to float it out? Answer no, but it won't matter because
+ -- we only float if arg' is a WHNF,
+ -- and so there can't be any 'will be demanded' bindings in the floats.
+ -- Hence the assert
+ WARN( any demanded_float (floatBinds floats),
+ ppr (filter demanded_float (floatBinds floats)) )
+
+ tick LetFloatFromLet `thenSmpl_` (
+ addFloats env1 floats $ \ env2 ->
+ addAtomicBinds env2 (fromOL aux_binds) $ \ env3 ->
+ completeLazyBind env3 top_lvl bndr bndr'' rhs2)
+
+ else
+ completeLazyBind env1 top_lvl bndr bndr'' (wrapFloats floats rhs1)
+
+#ifdef DEBUG
+demanded_float (NonRec b r) = isStrictDmd (idNewDemandInfo b) && not (isUnLiftedType (idType b))
+ -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
+demanded_float (Rec _) = False
+#endif
\end{code}
+
%************************************************************************
%* *
-\subsection{Simplify RHS of a Let/Letrec}
+\subsection{Completing a lazy binding}
%* *
%************************************************************************
-simplRhsExpr does arity-expansion. That is, given:
+completeLazyBind
+ * deals only with Ids, not TyVars
+ * takes an already-simplified binder and RHS
+ * is used for both recursive and non-recursive bindings
+ * is used for both top-level and non-top-level bindings
- * a right hand side /\ tyvars -> \a1 ... an -> e
- * the information (stored in BinderInfo) that the function will always
- be applied to at least k arguments
+It does the following:
+ - tries discarding a dead binding
+ - tries PostInlineUnconditionally
+ - add unfolding [this is the only place we add an unfolding]
+ - add arity
-it transforms the rhs to
-
- /\tyvars -> \a1 ... an b(n+1) ... bk -> (e b(n+1) ... bk)
-
-This is a Very Good Thing!
+It does *not* attempt to do let-to-case. Why? Because it is used for
+ - top-level bindings (when let-to-case is impossible)
+ - many situations where the "rhs" is known to be a WHNF
+ (so let-to-case is inappropriate).
\begin{code}
-simplRhsExpr
- :: SimplEnv
- -> InBinder
- -> InExpr
- -> OutId -- The new binder (used only for its type)
- -> SmplM (OutExpr, ArityInfo)
-\end{code}
-
-
-\begin{code}
-simplRhsExpr env binder@(id,occ_info) rhs new_id
- | maybeToBool (splitAlgTyConApp_maybe rhs_ty)
- -- Deal with the data type case, in which case the elaborate
- -- eta-expansion nonsense is really quite a waste of time.
- = simplExpr rhs_env rhs [] rhs_ty `thenSmpl` \ rhs' ->
- returnSmpl (rhs', ArityExactly 0)
-
- | otherwise -- OK, use the big hammer
- = -- Deal with the big lambda part
- simplTyBinders rhs_env tyvars `thenSmpl` \ (lam_env, tyvars') ->
- let
- body_ty = applyTys rhs_ty (mkTyVarTys tyvars')
+completeLazyBind :: SimplEnv
+ -> TopLevelFlag -- Flag stuck into unfolding
+ -> InId -- Old binder
+ -> OutId -- New binder
+ -> OutExpr -- Simplified RHS
+ -> SimplM (FloatsWith SimplEnv)
+-- We return a new SimplEnv, because completeLazyBind may choose to do its work
+-- by extending the substitution (e.g. let x = y in ...)
+-- The new binding (if any) is returned as part of the floats.
+-- NB: the returned SimplEnv has the right SubstEnv, but you should
+-- (as usual) use the in-scope-env from the floats
+
+completeLazyBind env top_lvl old_bndr new_bndr new_rhs
+ | postInlineUnconditionally env new_bndr occ_info new_rhs
+ = -- Drop the binding
+ tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
+ returnSmpl (emptyFloats env, extendSubst env old_bndr (DoneEx new_rhs))
+ -- Use the substitution to make quite, quite sure that the substitution
+ -- will happen, since we are going to discard the binding
+
+ | otherwise
+ = let
+ -- Add arity info
+ new_bndr_info = idInfo new_bndr `setArityInfo` exprArity new_rhs
+
+ -- Add the unfolding *only* for non-loop-breakers
+ -- Making loop breakers not have an unfolding at all
+ -- means that we can avoid tests in exprIsConApp, for example.
+ -- This is important: if exprIsConApp says 'yes' for a recursive
+ -- thing, then we can get into an infinite loop
+ info_w_unf | loop_breaker = new_bndr_info
+ | otherwise = new_bndr_info `setUnfoldingInfo` unfolding
+ unfolding = mkUnfolding (isTopLevel top_lvl) new_rhs
+
+ final_id = new_bndr `setIdInfo` info_w_unf
in
- -- Deal with the little lambda part
- -- Note that we call simplLam even if there are no binders,
- -- in case it can do arity expansion.
- simplValLam lam_env body (getBinderInfoArity occ_info) body_ty `thenSmpl` \ (lambda', arity) ->
+ -- These seqs forces the Id, and hence its IdInfo,
+ -- and hence any inner substitutions
+ final_id `seq`
+ returnSmpl (unitFloat env final_id new_rhs, env)
- -- Put on the big lambdas, trying to float out any bindings caught inside
- mkRhsTyLam tyvars' lambda' `thenSmpl` \ rhs' ->
+ where
+ loop_breaker = isLoopBreaker occ_info
+ old_info = idInfo old_bndr
+ occ_info = occInfo old_info
+\end{code}
- returnSmpl (rhs', arity)
- where
- rhs_ty = idType new_id
- rhs_env | idWantsToBeINLINEd id -- Don't ever inline in a INLINE thing's rhs
- = switchOffInlining env1 -- See comments with switchOffInlining
- | otherwise
- = env1
-
- -- The top level "enclosing CC" is "SUBSUMED". But the enclosing CC
- -- for the rhs of top level defs is "OST_CENTRE". Consider
- -- f = \x -> e
- -- g = \y -> let v = f y in scc "x" (v ...)
- -- Here we want to inline "f", since its CC is SUBSUMED, but we don't
- -- want to inline "v" since its CC is dynamically determined.
-
- current_cc = getEnclosingCC env
- env1 | costsAreSubsumed current_cc = setEnclosingCC env useCurrentCostCentre
- | otherwise = env
-
- (tyvars, body) = collectTyBinders rhs
-\end{code}
-----------------------------------------------------------------
- An old special case that is now nuked.
+%************************************************************************
+%* *
+\subsection[Simplify-simplExpr]{The main function: simplExpr}
+%* *
+%************************************************************************
-First a special case for variable right-hand sides
- v = w
-It's OK to simplify the RHS, but it's often a waste of time. Often
-these v = w things persist because v is exported, and w is used
-elsewhere. So if we're not careful we'll eta expand the rhs, only
-to eta reduce it in competeNonRec.
+The reason for this OutExprStuff stuff is that we want to float *after*
+simplifying a RHS, not before. If we do so naively we get quadratic
+behaviour as things float out.
-If we leave the binding unchanged, we will certainly replace v by w at
-every occurrence of v, which is good enough.
+To see why it's important to do it after, consider this (real) example:
-In fact, it's *better* to replace v by w than to inline w in v's rhs,
-even if this is the only occurrence of w. Why? Because w might have
-IdInfo (such as strictness) that v doesn't.
+ let t = f x
+ in fst t
+==>
+ let t = let a = e1
+ b = e2
+ in (a,b)
+ in fst t
+==>
+ let a = e1
+ b = e2
+ t = (a,b)
+ in
+ a -- Can't inline a this round, cos it appears twice
+==>
+ e1
-Furthermore, there might be other uses of w; if so, inlining w in
-v's rhs will duplicate w's rhs, whereas replacing v by w doesn't.
+Each of the ==> steps is a round of simplification. We'd save a
+whole round if we float first. This can cascade. Consider
-HOWEVER, we have to be careful if w is something that *must* be
-inlined. In particular, its binding may have been dropped. Here's
-an example that actually happened:
- let x = let y = e in y
- in f x
-The "let y" was floated out, and then (since y occurs once in a
-definitely inlinable position) the binding was dropped, leaving
- {y=e} let x = y in f x
-But now using the reasoning of this little section,
-y wasn't inlined, because it was a let x=y form.
+ let f = g d
+ in \x -> ...f...
+==>
+ let f = let d1 = ..d.. in \y -> e
+ in \x -> ...f...
+==>
+ let d1 = ..d..
+ in \x -> ...(\y ->e)...
+Only in this second round can the \y be applied, and it
+might do the same again.
- HOWEVER
-This "optimisation" turned out to be a bad idea. If there's are
-top-level exported bindings like
+\begin{code}
+simplExpr :: SimplEnv -> CoreExpr -> SimplM CoreExpr
+simplExpr env expr = simplExprC env expr (mkStop expr_ty' AnArg)
+ where
+ expr_ty' = substTy (getSubst env) (exprType expr)
+ -- The type in the Stop continuation, expr_ty', is usually not used
+ -- It's only needed when discarding continuations after finding
+ -- a function that returns bottom.
+ -- Hence the lazy substitution
+
+
+simplExprC :: SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
+ -- Simplify an expression, given a continuation
+simplExprC env expr cont
+ = simplExprF env expr cont `thenSmpl` \ (floats, expr) ->
+ returnSmpl (wrapFloats floats expr)
+
+simplExprF :: SimplEnv -> InExpr -> SimplCont -> SimplM FloatsWithExpr
+ -- Simplify an expression, returning floated binds
+
+simplExprF env (Var v) cont = simplVar env v cont
+simplExprF env (Lit lit) cont = rebuild env (Lit lit) cont
+simplExprF env expr@(Lam _ _) cont = simplLam env expr cont
+simplExprF env (Note note expr) cont = simplNote env note expr cont
+simplExprF env (App fun arg) cont = simplExprF env fun (ApplyTo NoDup arg env cont)
+
+simplExprF env (Type ty) cont
+ = ASSERT( contIsRhsOrArg cont )
+ simplType env ty `thenSmpl` \ ty' ->
+ rebuild env (Type ty') cont
+
+simplExprF env (Case scrut bndr alts) cont
+ | not (switchIsOn (getSwitchChecker env) NoCaseOfCase)
+ = -- Simplify the scrutinee with a Select continuation
+ simplExprF env scrut (Select NoDup bndr alts env cont)
- y = I# 3#
- x = y
+ | otherwise
+ = -- If case-of-case is off, simply simplify the case expression
+ -- in a vanilla Stop context, and rebuild the result around it
+ simplExprC env scrut case_cont `thenSmpl` \ case_expr' ->
+ rebuild env case_expr' cont
+ where
+ case_cont = Select NoDup bndr alts env (mkBoringStop (contResultType cont))
-then y wasn't getting inlined in x's rhs, and we were getting
-bad code. So I've removed the special case from here, and
-instead we only try eta reduction and constructor reuse
-in completeNonRec if the thing is *not* exported.
+simplExprF env (Let (Rec pairs) body) cont
+ = simplRecBndrs env (map fst pairs) `thenSmpl` \ (env, bndrs') ->
+ -- NB: bndrs' don't have unfoldings or spec-envs
+ -- We add them as we go down, using simplPrags
+ simplRecBind env NotTopLevel pairs bndrs' `thenSmpl` \ (floats, env) ->
+ addFloats env floats $ \ env ->
+ simplExprF env body cont
-\begin{pseudocode}
-simplRhsExpr env binder@(id,occ_info) (Var v) new_id
- | maybeToBool maybe_stop_at_var
- = returnSmpl (Var the_var, getIdArity the_var)
- where
- maybe_stop_at_var
- = case (runEager $ lookupId env v) of
- VarArg v' | not (must_unfold v') -> Just v'
- other -> Nothing
+-- A non-recursive let is dealt with by simplNonRecBind
+simplExprF env (Let (NonRec bndr rhs) body) cont
+ = simplNonRecBind env bndr rhs env (contResultType cont) $ \ env ->
+ simplExprF env body cont
- Just the_var = maybe_stop_at_var
- must_unfold v' = idMustBeINLINEd v'
- || case lookupOutIdEnv env v' of
- Just (_, _, InUnfolding _ _) -> True
- other -> False
-\end{pseudocode}
-
- End of old, nuked, special case.
-------------------------------------------------------------------
+---------------------------------
+simplType :: SimplEnv -> InType -> SimplM OutType
+ -- Kept monadic just so we can do the seqType
+simplType env ty
+ = seqType new_ty `seq` returnSmpl new_ty
+ where
+ new_ty = substTy (getSubst env) ty
+\end{code}
%************************************************************************
%* *
-\subsection{Simplify a lambda abstraction}
+\subsection{Lambdas}
%* *
%************************************************************************
-Simplify (\binders -> body) trying eta expansion and reduction, given that
-the abstraction will always be applied to at least min_no_of_args.
-
\begin{code}
-simplValLam env expr min_no_of_args expr_ty
- | not (switchIsSet env SimplDoLambdaEtaExpansion) || -- Bale out if eta expansion off
-
- exprIsTrivial expr || -- or it's a trivial RHS
- -- No eta expansion for trivial RHSs
- -- It's rather a Bad Thing to expand
- -- g = f alpha beta
- -- to
- -- g = \a b c -> f alpha beta a b c
- --
- -- The original RHS is "trivial" (exprIsTrivial), because it generates
- -- no code (renames f to g). But the new RHS isn't.
-
- null potential_extra_binder_tys || -- or ain't a function
- no_of_extra_binders <= 0 -- or no extra binders needed
- = simplBinders env binders `thenSmpl` \ (new_env, binders') ->
- simplExpr new_env body [] body_ty `thenSmpl` \ body' ->
- returnSmpl (mkValLam binders' body', final_arity)
-
- | otherwise -- Eta expansion possible
- = -- A SSERT( no_of_extra_binders <= length potential_extra_binder_tys )
- (if not ( no_of_extra_binders <= length potential_extra_binder_tys ) then
- pprTrace "simplValLam" (vcat [ppr expr,
- ppr expr_ty,
- ppr binders,
- int no_of_extra_binders,
- ppr potential_extra_binder_tys])
- else \x -> x) $
-
- tick EtaExpansion `thenSmpl_`
- simplBinders env binders `thenSmpl` \ (new_env, binders') ->
- newIds extra_binder_tys `thenSmpl` \ extra_binders' ->
- simplExpr new_env body (map VarArg extra_binders') etad_body_ty `thenSmpl` \ body' ->
- returnSmpl (
- mkValLam (binders' ++ extra_binders') body',
- final_arity
- )
+simplLam env fun cont
+ = go env fun cont
+ where
+ zap_it = mkLamBndrZapper fun (countArgs cont)
+ cont_ty = contResultType cont
+
+ -- Type-beta reduction
+ go env (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont)
+ = ASSERT( isTyVar bndr )
+ tick (BetaReduction bndr) `thenSmpl_`
+ simplType (setInScope arg_se env) ty_arg `thenSmpl` \ ty_arg' ->
+ go (extendSubst env bndr (DoneTy ty_arg')) body body_cont
+
+ -- Ordinary beta reduction
+ go env (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
+ = tick (BetaReduction bndr) `thenSmpl_`
+ simplNonRecBind env (zap_it bndr) arg arg_se cont_ty $ \ env ->
+ go env body body_cont
+
+ -- Not enough args, so there are real lambdas left to put in the result
+ go env lam@(Lam _ _) cont
+ = simplLamBndrs env bndrs `thenSmpl` \ (env, bndrs') ->
+ simplExpr env body `thenSmpl` \ body' ->
+ mkLam env bndrs' body' cont `thenSmpl` \ (floats, new_lam) ->
+ addFloats env floats $ \ env ->
+ rebuild env new_lam cont
+ where
+ (bndrs,body) = collectBinders lam
+
+ -- Exactly enough args
+ go env expr cont = simplExprF env expr cont
+mkLamBndrZapper :: CoreExpr -- Function
+ -> Int -- Number of args supplied, *including* type args
+ -> Id -> Id -- Use this to zap the binders
+mkLamBndrZapper fun n_args
+ | n_args >= n_params fun = \b -> b -- Enough args
+ | otherwise = \b -> zapLamIdInfo b
where
- (binders,body) = collectValBinders expr
- no_of_binders = length binders
- (arg_tys, res_ty) = splitFunTys expr_ty
- potential_extra_binder_tys = (if not (no_of_binders <= length arg_tys) then
- pprTrace "simplValLam" (vcat [ppr expr,
- ppr expr_ty,
- ppr binders])
- else \x->x) $
- drop no_of_binders arg_tys
- body_ty = mkFunTys potential_extra_binder_tys res_ty
-
- -- Note: it's possible that simplValLam will be applied to something
- -- with a forall type. Eg when being applied to the rhs of
- -- let x = wurble
- -- where wurble has a forall-type, but no big lambdas at the top.
- -- We could be clever an insert new big lambdas, but we don't bother.
-
- etad_body_ty = mkFunTys (drop no_of_extra_binders potential_extra_binder_tys) res_ty
- extra_binder_tys = take no_of_extra_binders potential_extra_binder_tys
- final_arity = atLeastArity (no_of_binders + no_of_extra_binders)
-
- no_of_extra_binders = -- First, use the info about how many args it's
- -- always applied to in its scope; but ignore this
- -- info for thunks. To see why we ignore it for thunks,
- -- consider let f = lookup env key in (f 1, f 2)
- -- We'd better not eta expand f just because it is
- -- always applied!
- (min_no_of_args - no_of_binders)
-
- -- Next, try seeing if there's a lambda hidden inside
- -- something cheap.
- -- etaExpandCount can reuturn a huge number (like 10000!) if
- -- it finds that the body is a call to "error"; hence
- -- the use of "min" here.
- `max`
- (etaExpandCount body `min` length potential_extra_binder_tys)
-
- -- Finally, see if it's a state transformer, in which
- -- case we eta-expand on principle! This can waste work,
- -- but usually doesn't
- `max`
- case potential_extra_binder_tys of
- [ty] | ty == realWorldStatePrimTy -> 1
- other -> 0
+ -- NB: we count all the args incl type args
+ -- so we must count all the binders (incl type lambdas)
+ n_params (Note _ e) = n_params e
+ n_params (Lam b e) = 1 + n_params e
+ n_params other = 0::Int
\end{code}
-
%************************************************************************
%* *
-\subsection[Simplify-coerce]{Coerce expressions}
+\subsection{Notes}
%* *
%************************************************************************
\begin{code}
--- (coerce (case s of p -> r)) args ==> case s of p -> (coerce r) args
-simplCoerce env coercion ty expr@(Case scrut alts) args result_ty
- = simplCase env scrut alts (\env rhs -> simplCoerce env coercion ty rhs args result_ty) result_ty
-
--- (coerce (let defns in b)) args ==> let defns' in (coerce b) args
-simplCoerce env coercion ty (Let bind body) args result_ty
- = simplBind env bind (\env -> simplCoerce env coercion ty body args result_ty) result_ty
-
--- Default case
-simplCoerce env coercion ty expr args result_ty
- = simplTy env ty `appEager` \ ty' ->
- simplTy env expr_ty `appEager` \ expr_ty' ->
- simplExpr env expr [] expr_ty' `thenSmpl` \ expr' ->
- returnSmpl (mkGenApp (mkCoerce coercion ty' expr') args)
- where
- expr_ty = coreExprType (unTagBinders expr) -- Rather like simplCase other_scrut
+simplNote env (Coerce to from) body cont
+ = let
+ in_scope = getInScope env
- -- Try cancellation; we do this "on the way up" because
- -- I think that's where it'll bite best
- mkCoerce (CoerceOut con1) ty1 (Coerce (CoerceIn con2) ty2 body) | con1 == con2 = body
- mkCoerce coercion ty body = Coerce coercion ty body
+ addCoerce s1 k1 (CoerceIt t1 cont)
+ -- coerce T1 S1 (coerce S1 K1 e)
+ -- ==>
+ -- e, if T1=K1
+ -- coerce T1 K1 e, otherwise
+ --
+ -- For example, in the initial form of a worker
+ -- we may find (coerce T (coerce S (\x.e))) y
+ -- and we'd like it to simplify to e[y/x] in one round
+ -- of simplification
+ | t1 `eqType` k1 = cont -- The coerces cancel out
+ | otherwise = CoerceIt t1 cont -- They don't cancel, but
+ -- the inner one is redundant
+
+ addCoerce t1t2 s1s2 (ApplyTo dup arg arg_se cont)
+ | Just (s1, s2) <- splitFunTy_maybe s1s2
+ -- (coerce (T1->T2) (S1->S2) F) E
+ -- ===>
+ -- coerce T2 S2 (F (coerce S1 T1 E))
+ --
+ -- t1t2 must be a function type, T1->T2
+ -- but s1s2 might conceivably not be
+ --
+ -- When we build the ApplyTo we can't mix the out-types
+ -- with the InExpr in the argument, so we simply substitute
+ -- to make it all consistent. It's a bit messy.
+ -- But it isn't a common case.
+ = let
+ (t1,t2) = splitFunTy t1t2
+ new_arg = mkCoerce2 s1 t1 (substExpr (mkSubst in_scope (getSubstEnv arg_se)) arg)
+ in
+ ApplyTo dup new_arg (zapSubstEnv env) (addCoerce t2 s2 cont)
+
+ addCoerce to' _ cont = CoerceIt to' cont
+ in
+ simplType env to `thenSmpl` \ to' ->
+ simplType env from `thenSmpl` \ from' ->
+ simplExprF env body (addCoerce to' from' cont)
+
+
+-- Hack: we only distinguish subsumed cost centre stacks for the purposes of
+-- inlining. All other CCCSs are mapped to currentCCS.
+simplNote env (SCC cc) e cont
+ = simplExpr (setEnclosingCC env currentCCS) e `thenSmpl` \ e' ->
+ rebuild env (mkSCC cc e') cont
+
+simplNote env InlineCall e cont
+ = simplExprF env e (InlinePlease cont)
+
+-- See notes with SimplMonad.inlineMode
+simplNote env InlineMe e cont
+ | contIsRhsOrArg cont -- Totally boring continuation; see notes above
+ = -- Don't inline inside an INLINE expression
+ simplExpr (setMode inlineMode env ) e `thenSmpl` \ e' ->
+ rebuild env (mkInlineMe e') cont
+
+ | otherwise -- Dissolve the InlineMe note if there's
+ -- an interesting context of any kind to combine with
+ -- (even a type application -- anything except Stop)
+ = simplExprF env e cont
\end{code}
%************************************************************************
%* *
-\subsection[Simplify-bind]{Binding groups}
+\subsection{Dealing with calls}
%* *
%************************************************************************
\begin{code}
-simplBind :: SimplEnv
- -> InBinding
- -> (SimplEnv -> SmplM OutExpr)
- -> OutType
- -> SmplM OutExpr
-
-simplBind env (NonRec binder rhs) body_c body_ty = simplNonRec env binder rhs body_c body_ty
-simplBind env (Rec pairs) body_c body_ty = simplRec env pairs body_c body_ty
-\end{code}
-
+simplVar env var cont
+ = case lookupIdSubst (getSubst env) var of
+ DoneEx e -> simplExprF (zapSubstEnv env) e cont
+ ContEx se e -> simplExprF (setSubstEnv env se) e cont
+ DoneId var1 occ -> WARN( not (isInScope var1 (getSubst env)) && mustHaveLocalBinding var1,
+ text "simplVar:" <+> ppr var )
+ completeCall (zapSubstEnv env) var1 occ cont
+ -- The template is already simplified, so don't re-substitute.
+ -- This is VITAL. Consider
+ -- let x = e in
+ -- let y = \z -> ...x... in
+ -- \ x -> ...y...
+ -- We'll clone the inner \x, adding x->x' in the id_subst
+ -- Then when we inline y, we must *not* replace x by x' in
+ -- the inlined copy!!
+
+---------------------------------------------------------
+-- Dealing with a call site
+
+completeCall env var occ_info cont
+ = -- Simplify the arguments
+ getDOptsSmpl `thenSmpl` \ dflags ->
+ let
+ chkr = getSwitchChecker env
+ (args, call_cont, inline_call) = getContArgs chkr var cont
+ fn_ty = idType var
+ in
+ simplifyArgs env fn_ty args (contResultType call_cont) $ \ env args ->
-%************************************************************************
-%* *
-\subsection[Simplify-let]{Let-expressions}
-%* *
-%************************************************************************
+ -- Next, look for rules or specialisations that match
+ --
+ -- It's important to simplify the args first, because the rule-matcher
+ -- doesn't do substitution as it goes. We don't want to use subst_args
+ -- (defined in the 'where') because that throws away useful occurrence info,
+ -- and perhaps-very-important specialisations.
+ --
+ -- Some functions have specialisations *and* are strict; in this case,
+ -- we don't want to inline the wrapper of the non-specialised thing; better
+ -- to call the specialised thing instead.
+ -- We used to use the black-listing mechanism to ensure that inlining of
+ -- the wrapper didn't occur for things that have specialisations till a
+ -- later phase, so but now we just try RULES first
+ --
+ -- You might think that we shouldn't apply rules for a loop breaker:
+ -- doing so might give rise to an infinite loop, because a RULE is
+ -- rather like an extra equation for the function:
+ -- RULE: f (g x) y = x+y
+ -- Eqn: f a y = a-y
+ --
+ -- But it's too drastic to disable rules for loop breakers.
+ -- Even the foldr/build rule would be disabled, because foldr
+ -- is recursive, and hence a loop breaker:
+ -- foldr k z (build g) = g k z
+ -- So it's up to the programmer: rules can cause divergence
-Float switches
-~~~~~~~~~~~~~~
-The booleans controlling floating have to be set with a little care.
-Here's one performance bug I found:
+ let
+ in_scope = getInScope env
+ maybe_rule = case activeRule env of
+ Nothing -> Nothing -- No rules apply
+ Just act_fn -> lookupRule act_fn in_scope var args
+ in
+ case maybe_rule of {
+ Just (rule_name, rule_rhs) ->
+ tick (RuleFired rule_name) `thenSmpl_`
+ (if dopt Opt_D_dump_inlinings dflags then
+ pprTrace "Rule fired" (vcat [
+ text "Rule:" <+> ptext rule_name,
+ text "Before:" <+> ppr var <+> sep (map pprParendExpr args),
+ text "After: " <+> pprCoreExpr rule_rhs,
+ text "Cont: " <+> ppr call_cont])
+ else
+ id) $
+ simplExprF env rule_rhs call_cont ;
+
+ Nothing -> -- No rules
- let x = let y = let z = case a# +# 1 of {b# -> E1}
- in E2
- in E3
- in E4
+ -- Next, look for an inlining
+ let
+ arg_infos = [ interestingArg arg | arg <- args, isValArg arg]
-Now, if E2, E3 aren't HNFs we won't float the y-binding or the z-binding.
-Before case_floating_ok included float_exposes_hnf, the case expression was floated
-*one level per simplifier iteration* outwards. So it made th s
+ interesting_cont = interestingCallContext (notNull args)
+ (notNull arg_infos)
+ call_cont
+ active_inline = activeInline env var occ_info
+ maybe_inline = callSiteInline dflags active_inline inline_call occ_info
+ var arg_infos interesting_cont
+ in
+ case maybe_inline of {
+ Just unfolding -- There is an inlining!
+ -> tick (UnfoldingDone var) `thenSmpl_`
+ makeThatCall env var unfolding args call_cont
+
+ ;
+ Nothing -> -- No inlining!
+
+ -- Done
+ rebuild env (mkApps (Var var) args) call_cont
+ }}
+
+makeThatCall :: SimplEnv
+ -> Id
+ -> InExpr -- Inlined function rhs
+ -> [OutExpr] -- Arguments, already simplified
+ -> SimplCont -- After the call
+ -> SimplM FloatsWithExpr
+-- Similar to simplLam, but this time
+-- the arguments are already simplified
+makeThatCall orig_env var fun@(Lam _ _) args cont
+ = go orig_env fun args
+ where
+ zap_it = mkLamBndrZapper fun (length args)
-Floating case from let
-~~~~~~~~~~~~~~~~~~~~~~
-When floating cases out of lets, remember this:
+ -- Type-beta reduction
+ go env (Lam bndr body) (Type ty_arg : args)
+ = ASSERT( isTyVar bndr )
+ tick (BetaReduction bndr) `thenSmpl_`
+ go (extendSubst env bndr (DoneTy ty_arg)) body args
- let x* = case e of alts
- in <small expr>
+ -- Ordinary beta reduction
+ go env (Lam bndr body) (arg : args)
+ = tick (BetaReduction bndr) `thenSmpl_`
+ simplNonRecX env (zap_it bndr) arg $ \ env ->
+ go env body args
-where x* is sure to be demanded or e is a cheap operation that cannot
-fail, e.g. unboxed addition. Here we should be prepared to duplicate
-<small expr>. A good example:
+ -- Not enough args, so there are real lambdas left to put in the result
+ go env fun args
+ = simplExprF env fun (pushContArgs orig_env args cont)
+ -- NB: orig_env; the correct environment to capture with
+ -- the arguments.... env has been augmented with substitutions
+ -- from the beta reductions.
- let x* = case y of
- p1 -> build e1
- p2 -> build e2
- in
- foldr c n x*
-==>
- case y of
- p1 -> foldr c n (build e1)
- p2 -> foldr c n (build e2)
+makeThatCall env var fun args cont
+ = simplExprF env fun (pushContArgs env args cont)
+\end{code}
-NEW: We use the same machinery that we use for case-of-case to
-*always* do case floating from let, that is we let bind and abstract
-the original let body, and let the occurrence analyser later decide
-whether the new let should be inlined or not. The example above
-becomes:
-==>
- let join_body x' = foldr c n x'
- in case y of
- p1 -> let x* = build e1
- in join_body x*
- p2 -> let x* = build e2
- in join_body x*
+%************************************************************************
+%* *
+\subsection{Arguments}
+%* *
+%************************************************************************
-note that join_body is a let-no-escape.
-In this particular example join_body will later be inlined,
-achieving the same effect.
-ToDo: check this is OK with andy
+\begin{code}
+---------------------------------------------------------
+-- Simplifying the arguments of a call
+
+simplifyArgs :: SimplEnv
+ -> OutType -- Type of the function
+ -> [(InExpr, SimplEnv, Bool)] -- Details of the arguments
+ -> OutType -- Type of the continuation
+ -> (SimplEnv -> [OutExpr] -> SimplM FloatsWithExpr)
+ -> SimplM FloatsWithExpr
+
+-- [CPS-like because of strict arguments]
+
+-- Simplify the arguments to a call.
+-- This part of the simplifier may break the no-shadowing invariant
+-- Consider
+-- f (...(\a -> e)...) (case y of (a,b) -> e')
+-- where f is strict in its second arg
+-- If we simplify the innermost one first we get (...(\a -> e)...)
+-- Simplifying the second arg makes us float the case out, so we end up with
+-- case y of (a,b) -> f (...(\a -> e)...) e'
+-- So the output does not have the no-shadowing invariant. However, there is
+-- no danger of getting name-capture, because when the first arg was simplified
+-- we used an in-scope set that at least mentioned all the variables free in its
+-- static environment, and that is enough.
+--
+-- We can't just do innermost first, or we'd end up with a dual problem:
+-- case x of (a,b) -> f e (...(\a -> e')...)
+--
+-- I spent hours trying to recover the no-shadowing invariant, but I just could
+-- not think of an elegant way to do it. The simplifier is already knee-deep in
+-- continuations. We have to keep the right in-scope set around; AND we have
+-- to get the effect that finding (error "foo") in a strict arg position will
+-- discard the entire application and replace it with (error "foo"). Getting
+-- all this at once is TOO HARD!
+
+simplifyArgs env fn_ty args cont_ty thing_inside
+ = go env fn_ty args thing_inside
+ where
+ go env fn_ty [] thing_inside = thing_inside env []
+ go env fn_ty (arg:args) thing_inside = simplifyArg env fn_ty arg cont_ty $ \ env arg' ->
+ go env (applyTypeToArg fn_ty arg') args $ \ env args' ->
+ thing_inside env (arg':args')
+simplifyArg env fn_ty (Type ty_arg, se, _) cont_ty thing_inside
+ = simplType (setInScope se env) ty_arg `thenSmpl` \ new_ty_arg ->
+ thing_inside env (Type new_ty_arg)
-Let to case: two points
-~~~~~~~~~~~
+simplifyArg env fn_ty (val_arg, arg_se, is_strict) cont_ty thing_inside
+ | is_strict
+ = simplStrictArg AnArg env val_arg arg_se arg_ty cont_ty thing_inside
-Point 1. We defer let-to-case for all data types except single-constructor
-ones. Suppose we change
+ | otherwise
+ = simplExprF (setInScope arg_se env) val_arg
+ (mkStop arg_ty AnArg) `thenSmpl` \ (floats, arg1) ->
+ addFloats env floats $ \ env ->
+ thing_inside env arg1
+ where
+ arg_ty = funArgTy fn_ty
+
+
+simplStrictArg :: LetRhsFlag
+ -> SimplEnv -- The env of the call
+ -> InExpr -> SimplEnv -- The arg plus its env
+ -> OutType -- arg_ty: type of the argument
+ -> OutType -- cont_ty: Type of thing computed by the context
+ -> (SimplEnv -> OutExpr -> SimplM FloatsWithExpr)
+ -- Takes an expression of type rhs_ty,
+ -- returns an expression of type cont_ty
+ -- The env passed to this continuation is the
+ -- env of the call, plus any new in-scope variables
+ -> SimplM FloatsWithExpr -- An expression of type cont_ty
+
+simplStrictArg is_rhs call_env arg arg_env arg_ty cont_ty thing_inside
+ = simplExprF (setInScope arg_env call_env) arg
+ (ArgOf is_rhs arg_ty cont_ty (\ new_env -> thing_inside (setInScope call_env new_env)))
+ -- Notice the way we use arg_env (augmented with in-scope vars from call_env)
+ -- to simplify the argument
+ -- and call-env (augmented with in-scope vars from the arg) to pass to the continuation
+\end{code}
- let x* = e in b
-to
- case e of x -> b
-It can be the case that we find that b ultimately contains ...(case x of ..)....
-and this is the only occurrence of x. Then if we've done let-to-case
-we can't inline x, which is a real pain. On the other hand, we lose no
-transformations by not doing this transformation, because the relevant
-case-of-X transformations are also implemented by simpl_bind.
+%************************************************************************
+%* *
+\subsection{mkAtomicArgs}
+%* *
+%************************************************************************
-If x is a single-constructor type, then we go ahead anyway, giving
+mkAtomicArgs takes a putative RHS, checks whether it's a PAP or
+constructor application and, if so, converts it to ANF, so that the
+resulting thing can be inlined more easily. Thus
+ x = (f a, g b)
+becomes
+ t1 = f a
+ t2 = g b
+ x = (t1,t2)
- case e of (y,z) -> let x = (y,z) in b
+There are three sorts of binding context, specified by the two
+boolean arguments
-because now we can squash case-on-x wherever they occur in b.
+Strict
+ OK-unlifted
-We do let-to-case on multi-constructor types in the tidy-up phase
-(tidyCoreExpr) mainly so that the code generator doesn't need to
-spot the demand-flag.
+N N Top-level or recursive Only bind args of lifted type
+N Y Non-top-level and non-recursive, Bind args of lifted type, or
+ but lazy unlifted-and-ok-for-speculation
-Point 2. It's important to try let-to-case before doing the
-strict-let-of-case transformation, which happens in the next equation
-for simpl_bind.
+Y Y Non-top-level, non-recursive, Bind all args
+ and strict (demanded)
+
- let a*::Int = case v of {p1->e1; p2->e2}
- in b
+For example, given
-(The * means that a is sure to be demanded.)
-If we do case-floating first we get this:
+ x = MkC (y div# z)
- let k = \a* -> b
- in case v of
- p1-> let a*=e1 in k a
- p2-> let a*=e2 in k a
+there is no point in transforming to
-Now watch what happens if we do let-to-case first:
+ x = case (y div# z) of r -> MkC r
- case (case v of {p1->e1; p2->e2}) of
- Int a# -> let a*=I# a# in b
-===>
- let k = \a# -> let a*=I# a# in b
- in case v of
- p1 -> case e1 of I# a# -> k a#
- p1 -> case e2 of I# a# -> k a#
+because the (y div# z) can't float out of the let. But if it was
+a *strict* let, then it would be a good thing to do. Hence the
+context information.
-The latter is clearly better. (Remember the reboxing let-decl for a
-is likely to go away, because after all b is strict in a.)
+\begin{code}
+mkAtomicArgs :: Bool -- A strict binding
+ -> Bool -- OK to float unlifted args
+ -> OutExpr
+ -> SimplM (OrdList (OutId,OutExpr), -- The floats (unusually) may include
+ OutExpr) -- things that need case-binding,
+ -- if the strict-binding flag is on
-We do not do let to case for WHNFs, e.g.
+mkAtomicArgs is_strict ok_float_unlifted rhs
+ | (Var fun, args) <- collectArgs rhs, -- It's an application
+ isDataConId fun || valArgCount args < idArity fun -- And it's a constructor or PAP
+ = go fun nilOL [] args -- Have a go
- let x = a:b in ...
- =/=>
- case a:b of x in ...
+ | otherwise = bale_out -- Give up
-as this is less efficient. but we don't mind doing let-to-case for
-"bottom", as that will allow us to remove more dead code, if anything:
+ where
+ bale_out = returnSmpl (nilOL, rhs)
+
+ go fun binds rev_args []
+ = returnSmpl (binds, mkApps (Var fun) (reverse rev_args))
+
+ go fun binds rev_args (arg : args)
+ | exprIsTrivial arg -- Easy case
+ = go fun binds (arg:rev_args) args
+
+ | not can_float_arg -- Can't make this arg atomic
+ = bale_out -- ... so give up
+
+ | otherwise -- Don't forget to do it recursively
+ -- E.g. x = a:b:c:[]
+ = mkAtomicArgs is_strict ok_float_unlifted arg `thenSmpl` \ (arg_binds, arg') ->
+ newId FSLIT("a") arg_ty `thenSmpl` \ arg_id ->
+ go fun ((arg_binds `snocOL` (arg_id,arg')) `appOL` binds)
+ (Var arg_id : rev_args) args
+ where
+ arg_ty = exprType arg
+ can_float_arg = is_strict
+ || not (isUnLiftedType arg_ty)
+ || (ok_float_unlifted && exprOkForSpeculation arg)
+
+
+addAtomicBinds :: SimplEnv -> [(OutId,OutExpr)]
+ -> (SimplEnv -> SimplM (FloatsWith a))
+ -> SimplM (FloatsWith a)
+addAtomicBinds env [] thing_inside = thing_inside env
+addAtomicBinds env ((v,r):bs) thing_inside = addAuxiliaryBind env (NonRec v r) $ \ env ->
+ addAtomicBinds env bs thing_inside
+
+addAtomicBindsE :: SimplEnv -> [(OutId,OutExpr)]
+ -> (SimplEnv -> SimplM FloatsWithExpr)
+ -> SimplM FloatsWithExpr
+-- Same again, but this time we're in an expression context,
+-- and may need to do some case bindings
+
+addAtomicBindsE env [] thing_inside
+ = thing_inside env
+addAtomicBindsE env ((v,r):bs) thing_inside
+ | needsCaseBinding (idType v) r
+ = addAtomicBindsE (addNewInScopeIds env [v]) bs thing_inside `thenSmpl` \ (floats, expr) ->
+ WARN( exprIsTrivial expr, ppr v <+> pprCoreExpr expr )
+ returnSmpl (emptyFloats env, Case r v [(DEFAULT,[], wrapFloats floats expr)])
- let x = error in ...
- ===>
- case error of x -> ...
- ===>
- error
+ | otherwise
+ = addAuxiliaryBind env (NonRec v r) $ \ env ->
+ addAtomicBindsE env bs thing_inside
+\end{code}
-Notice that let to case occurs only if x is used strictly in its body
-(obviously).
+%************************************************************************
+%* *
+\subsection{The main rebuilder}
+%* *
+%************************************************************************
\begin{code}
--- Dead code is now discarded by the occurrence analyser,
-
-simplNonRec env binder@(id,_) rhs body_c body_ty
- | inlineUnconditionally ok_to_dup binder
- = -- The binder is used in definitely-inline way in the body
- -- So add it to the environment, drop the binding, and continue
- body_c (bindIdToExpr env binder rhs)
-
- | idWantsToBeINLINEd id
- = complete_bind env rhs -- Don't mess about with floating or let-to-case on
- -- INLINE things
-
- -- Do let-to-case right away for unpointed types
- -- These shouldn't occur much, but do occur right after desugaring,
- -- because we havn't done dependency analysis at that point, so
- -- we can't trivially do let-to-case (because there may be some unboxed
- -- things bound in letrecs that aren't really recursive).
- | isUnpointedType rhs_ty && not rhs_is_whnf
- = simplCase env rhs (PrimAlts [] (BindDefault binder (Var id)))
- (\env rhs -> complete_bind env rhs) body_ty
-
- -- Try let-to-case; see notes below about let-to-case
- | try_let_to_case &&
- will_be_demanded &&
- ( rhs_is_bot
- || (not rhs_is_whnf && singleConstructorType rhs_ty)
- -- Don't do let-to-case if the RHS is a constructor application.
- -- Even then only do it for single constructor types.
- -- For other types we defer doing it until the tidy-up phase at
- -- the end of simplification.
- )
- = tick Let2Case `thenSmpl_`
- simplCase env rhs (AlgAlts [] (BindDefault binder (Var id)))
- (\env rhs -> complete_bind env rhs) body_ty
- -- OLD COMMENT: [now the new RHS is only "x" so there's less worry]
- -- NB: it's tidier to call complete_bind not simpl_bind, else
- -- we nearly end up in a loop. Consider:
- -- let x = rhs in b
- -- ==> case rhs of (p,q) -> let x=(p,q) in b
- -- This effectively what the above simplCase call does.
- -- Now, the inner let is a let-to-case target again! Actually, since
- -- the RHS is in WHNF it won't happen, but it's a close thing!
+rebuild :: SimplEnv -> OutExpr -> SimplCont -> SimplM FloatsWithExpr
- | otherwise
- = simpl_bind env rhs
- where
- -- Try let-from-let
- simpl_bind env (Let bind rhs) | let_floating_ok
- = tick LetFloatFromLet `thenSmpl_`
- simplBind env (if will_be_demanded then bind
- else un_demandify_bind bind)
- (\env -> simpl_bind env rhs) body_ty
-
- -- Try case-from-let; this deals with a strict let of error too
- simpl_bind env (Case scrut alts) | case_floating_ok scrut
- = tick CaseFloatFromLet `thenSmpl_`
-
- -- First, bind large let-body if necessary
- if ok_to_dup || isSingleton (nonErrorRHSs alts)
- then
- simplCase env scrut alts (\env rhs -> simpl_bind env rhs) body_ty
- else
- bindLargeRhs env [binder] body_ty body_c `thenSmpl` \ (extra_binding, new_body) ->
- let
- body_c' = \env -> simplExpr env new_body [] body_ty
- case_c = \env rhs -> simplNonRec env binder rhs body_c' body_ty
- in
- simplCase env scrut alts case_c body_ty `thenSmpl` \ case_expr ->
- returnSmpl (Let extra_binding case_expr)
+rebuild env expr (Stop _ _ _) = rebuildDone env expr
+rebuild env expr (ArgOf _ _ _ cont_fn) = cont_fn env expr
+rebuild env expr (CoerceIt to_ty cont) = rebuild env (mkCoerce to_ty expr) cont
+rebuild env expr (InlinePlease cont) = rebuild env (Note InlineCall expr) cont
+rebuild env expr (Select _ bndr alts se cont) = rebuildCase (setInScope se env) expr bndr alts cont
+rebuild env expr (ApplyTo _ arg se cont) = rebuildApp (setInScope se env) expr arg cont
- -- None of the above; simplify rhs and tidy up
- simpl_bind env rhs = complete_bind env rhs
-
- complete_bind env rhs
- = simplBinder env binder `thenSmpl` \ (env_w_clone, new_id) ->
- simplRhsExpr env binder rhs new_id `thenSmpl` \ (rhs',arity) ->
- completeNonRec env_w_clone binder
- (new_id `withArity` arity) rhs' `thenSmpl` \ (new_env, binds) ->
- body_c new_env `thenSmpl` \ body' ->
- returnSmpl (mkCoLetsAny binds body')
-
-
- -- All this stuff is computed at the start of the simpl_bind loop
- float_lets = switchIsSet env SimplFloatLetsExposingWHNF
- float_primops = switchIsSet env SimplOkToFloatPrimOps
- ok_to_dup = switchIsSet env SimplOkToDupCode
- always_float_let_from_let = switchIsSet env SimplAlwaysFloatLetsFromLets
- try_let_to_case = switchIsSet env SimplLetToCase
- no_float = switchIsSet env SimplNoLetFromStrictLet
-
- demand_info = getIdDemandInfo id
- will_be_demanded = willBeDemanded demand_info
- rhs_ty = idType id
-
- form = mkFormSummary rhs
- rhs_is_bot = case form of
- BottomForm -> True
- other -> False
- rhs_is_whnf = case form of
- VarForm -> True
- ValueForm -> True
- other -> False
-
- float_exposes_hnf = floatExposesHNF float_lets float_primops ok_to_dup rhs
-
- let_floating_ok = (will_be_demanded && not no_float) ||
- always_float_let_from_let ||
- float_exposes_hnf
-
- case_floating_ok scrut = (will_be_demanded && not no_float) ||
- (float_exposes_hnf && is_cheap_prim_app scrut && float_primops)
- -- See note below
+rebuildApp env fun arg cont
+ = simplExpr env arg `thenSmpl` \ arg' ->
+ rebuild env (App fun arg') cont
+
+rebuildDone env expr = returnSmpl (emptyFloats env, expr)
\end{code}
-@completeNonRec@ looks at the simplified post-floating RHS of the
-let-expression, with a view to turning
- x = e
-into
- x = y
-where y is just a variable. Now we can eliminate the binding
-altogether, and replace x by y throughout.
+%************************************************************************
+%* *
+\subsection{Functions dealing with a case}
+%* *
+%************************************************************************
-There are two cases when we can do this:
+Blob of helper functions for the "case-of-something-else" situation.
- * When e is a constructor application, and we have
- another variable in scope bound to the same
- constructor application. [This is just a special
- case of common-subexpression elimination.]
+\begin{code}
+---------------------------------------------------------
+-- Eliminate the case if possible
+
+rebuildCase :: SimplEnv
+ -> OutExpr -- Scrutinee
+ -> InId -- Case binder
+ -> [InAlt] -- Alternatives
+ -> SimplCont
+ -> SimplM FloatsWithExpr
+
+rebuildCase env scrut case_bndr alts cont
+ | Just (con,args) <- exprIsConApp_maybe scrut
+ -- Works when the scrutinee is a variable with a known unfolding
+ -- as well as when it's an explicit constructor application
+ = knownCon env (DataAlt con) args case_bndr alts cont
+
+ | Lit lit <- scrut -- No need for same treatment as constructors
+ -- because literals are inlined more vigorously
+ = knownCon env (LitAlt lit) [] case_bndr alts cont
- * When e can be eta-reduced to a variable. E.g.
- x = \a b -> y a b
+ | otherwise
+ = prepareAlts scrut case_bndr alts `thenSmpl` \ (better_alts, handled_cons) ->
+ -- Deal with the case binder, and prepare the continuation;
+ -- The new subst_env is in place
+ prepareCaseCont env better_alts cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
+ addFloats env floats $ \ env ->
-HOWEVER, if x is exported, we don't attempt this at all. Why not?
-Because then we can't remove the x=y binding, in which case we
-have just made things worse, perhaps a lot worse.
+ -- Deal with variable scrutinee
+ simplCaseBinder env scrut case_bndr `thenSmpl` \ (alt_env, case_bndr', zap_occ_info) ->
-\begin{code}
-completeNonRec env binder new_id new_rhs
- = returnSmpl (env', [NonRec b r | (b,r) <- binds])
- where
- (env', binds) = completeBind env binder new_id new_rhs
+ -- Deal with the case alternatives
+ simplAlts alt_env zap_occ_info handled_cons
+ case_bndr' better_alts dup_cont `thenSmpl` \ alts' ->
+ -- Put the case back together
+ mkCase scrut case_bndr' alts' `thenSmpl` \ case_expr ->
-completeBind :: SimplEnv
- -> InBinder -> OutId -> OutExpr -- Id and RHS
- -> (SimplEnv, [(OutId, OutExpr)]) -- Final envt and binding(s)
+ -- Notice that rebuildDone returns the in-scope set from env, not alt_env
+ -- The case binder *not* scope over the whole returned case-expression
+ rebuild env case_expr nondup_cont
+\end{code}
-completeBind env binder@(_,occ_info) new_id new_rhs
- | idMustNotBeINLINEd new_id -- Occurrence analyser says "don't inline"
- = (env, new_binds)
+simplCaseBinder checks whether the scrutinee is a variable, v. If so,
+try to eliminate uses of v in the RHSs in favour of case_bndr; that
+way, there's a chance that v will now only be used once, and hence
+inlined.
- | atomic_rhs -- If rhs (after eta reduction) is atomic
- && not (isExported new_id) -- and binder isn't exported
- = -- Drop the binding completely
- let
- env1 = notInScope env new_id
- env2 = bindIdToAtom env1 binder the_arg
- in
- (env2, [])
+Note 1
+~~~~~~
+There is a time we *don't* want to do that, namely when
+-fno-case-of-case is on. This happens in the first simplifier pass,
+and enhances full laziness. Here's the bad case:
+ f = \ y -> ...(case x of I# v -> ...(case x of ...) ... )
+If we eliminate the inner case, we trap it inside the I# v -> arm,
+which might prevent some full laziness happening. I've seen this
+in action in spectral/cichelli/Prog.hs:
+ [(m,n) | m <- [1..max], n <- [1..max]]
+Hence the check for NoCaseOfCase.
- | atomic_rhs -- Rhs is atomic, and new_id is exported
- && case eta'd_rhs of { Var v -> isLocallyDefined v && not (isExported v); other -> False }
- = -- The local variable v will be eliminated next time round
- -- in favour of new_id, so it's a waste to replace all new_id's with v's
- -- this time round.
- -- This case is an optional improvement; saves a simplifier iteration
- (env, [(new_id, eta'd_rhs)])
+Note 2
+~~~~~~
+There is another situation when we don't want to do it. If we have
- | otherwise -- Non-atomic
- = let
- env1 = extendEnvGivenBinding env occ_info new_id new_rhs
- in
- (env1, new_binds)
-
- where
- new_binds = [(new_id, new_rhs)]
- atomic_rhs = is_atomic eta'd_rhs
- eta'd_rhs = case lookForConstructor env new_rhs of
- Just v -> Var v
- other -> etaCoreExpr new_rhs
-
- the_arg = case eta'd_rhs of
- Var v -> VarArg v
- Lit l -> LitArg l
-\end{code}
+ case x of w1 { DEFAULT -> case x of w2 { A -> e1; B -> e2 }
+ ...other cases .... }
-----------------------------------------------------------------------------
- A digression on constructor CSE
-
-Consider
-@
- f = \x -> case x of
- (y:ys) -> y:ys
- [] -> ...
-@
-Is it a good idea to replace the rhs @y:ys@ with @x@? This depends a
-bit on the compiler technology, but in general I believe not. For
-example, here's some code from a real program:
-@
-const.Int.max.wrk{-s2516-} =
- \ upk.s3297# upk.s3298# ->
- let {
- a.s3299 :: Int
- _N_ {-# U(P) #-}
- a.s3299 = I#! upk.s3297#
- } in
- case (const.Int._tagCmp.wrk{-s2513-} upk.s3297# upk.s3298#) of {
- _LT -> I#! upk.s3298#
- _EQ -> a.s3299
- _GT -> a.s3299
- }
-@
-The a.s3299 really isn't doing much good. We'd be better off inlining
-it. (Actually, let-no-escapery means it isn't as bad as it looks.)
-
-So the current strategy is to inline all known-form constructors, and
-only do the reverse (turn a constructor application back into a
-variable) when we find a let-expression:
-@
- let x = C a1 .. an
- in
- ... (let y = C a1 .. an in ...) ...
-@
-where it is always good to ditch the binding for y, and replace y by
-x.
- End of digression
-----------------------------------------------------------------------------
-
-----------------------------------------------------------------------------
- A digression on "optimising" coercions
-
- The trouble is that we kept transforming
- let x = coerce e
- y = coerce x
- in ...
- to
- let x' = coerce e
- y' = coerce x'
- in ...
- and counting a couple of ticks for this non-transformation
-\begin{pseudocode}
- -- We want to ensure that all let-bound Coerces have
- -- atomic bodies, so they can freely be inlined.
-completeNonRec env binder new_id (Coerce coercion ty rhs)
- | not (is_atomic rhs)
- = newId (coreExprType rhs) `thenSmpl` \ inner_id ->
- completeNonRec env
- (inner_id, dangerousArgOcc) inner_id rhs `thenSmpl` \ (env1, binds1) ->
- -- Dangerous occ because, like constructor args,
- -- it can be duplicated easily
- let
- atomic_rhs = case runEager $ lookupId env1 inner_id of
- LitArg l -> Lit l
- VarArg v -> Var v
- in
- completeNonRec env1 binder new_id
- (Coerce coercion ty atomic_rhs) `thenSmpl` \ (env2, binds2) ->
+We'll perform the binder-swap for the outer case, giving
- returnSmpl (env2, binds1 ++ binds2)
-\end{pseudocode}
-----------------------------------------------------------------------------
+ case x of w1 { DEFAULT -> case w1 of w2 { A -> e1; B -> e2 }
+ ...other cases .... }
+But there is no point in doing it for the inner case, because w1 can't
+be inlined anyway. Furthermore, doing the case-swapping involves
+zapping w2's occurrence info (see paragraphs that follow), and that
+forces us to bind w2 when doing case merging. So we get
+ case x of w1 { A -> let w2 = w1 in e1
+ B -> let w2 = w1 in e2
+ ...other cases .... }
-%************************************************************************
-%* *
-\subsection[Simplify-letrec]{Letrec-expressions}
-%* *
-%************************************************************************
+This is plain silly in the common case where w2 is dead.
-Letrec expressions
-~~~~~~~~~~~~~~~~~~
-Here's the game plan
+Even so, I can't see a good way to implement this idea. I tried
+not doing the binder-swap if the scrutinee was already evaluated
+but that failed big-time:
-1. Float any let(rec)s out of the RHSs
-2. Clone all the Ids and extend the envt with these clones
-3. Simplify one binding at a time, adding each binding to the
- environment once it's done.
+ data T = MkT !Int
-This relies on the occurrence analyser to
- a) break all cycles with an Id marked MustNotBeInlined
- b) sort the decls into topological order
-The former prevents infinite inlinings, and the latter means
-that we get maximum benefit from working top to bottom.
+ case v of w { MkT x ->
+ case x of x1 { I# y1 ->
+ case x of x2 { I# y2 -> ...
+Notice that because MkT is strict, x is marked "evaluated". But to
+eliminate the last case, we must either make sure that x (as well as
+x1) has unfolding MkT y1. THe straightforward thing to do is to do
+the binder-swap. So this whole note is a no-op.
-\begin{code}
-simplRec env pairs body_c body_ty
- = -- Do floating, if necessary
- floatBind env False (Rec pairs) `thenSmpl` \ [Rec pairs'] ->
- let
- binders = map fst pairs'
- in
- simplBinders env binders `thenSmpl` \ (env_w_clones, ids') ->
- simplRecursiveGroup env_w_clones ids' pairs' `thenSmpl` \ (pairs', new_env) ->
+Note 3
+~~~~~~
+If we replace the scrutinee, v, by tbe case binder, then we have to nuke
+any occurrence info (eg IAmDead) in the case binder, because the
+case-binder now effectively occurs whenever v does. AND we have to do
+the same for the pattern-bound variables! Example:
- body_c new_env `thenSmpl` \ body' ->
+ (case x of { (a,b) -> a }) (case x of { (p,q) -> q })
- returnSmpl (Let (Rec pairs') body')
-\end{code}
+Here, b and p are dead. But when we move the argment inside the first
+case RHS, and eliminate the second case, we get
+
+ case x or { (a,b) -> a b }
+
+Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
+happened. Hence the zap_occ_info function returned by simplCaseBinder
\begin{code}
--- The env passed to simplRecursiveGroup already has
--- bindings that clone the variables of the group.
-simplRecursiveGroup env new_ids []
- = returnSmpl ([], env)
-
-simplRecursiveGroup env (new_id : new_ids) ((binder, rhs) : pairs)
- | inlineUnconditionally ok_to_dup binder
- = -- Single occurrence, so drop binding and extend env with the inlining
- -- This is a little delicate, because what if the unique occurrence
- -- is *before* this binding? This'll never happen, because
- -- either it'll be marked "never inline" or else its occurrence will
- -- occur after its binding in the group.
- --
- -- If these claims aren't right Core Lint will spot an unbound
- -- variable. A quick fix is to delete this clause for simplRecursiveGroup
- let
- new_env = bindIdToExpr env binder rhs
- in
- simplRecursiveGroup new_env new_ids pairs
+simplCaseBinder env (Var v) case_bndr
+ | not (switchIsOn (getSwitchChecker env) NoCaseOfCase)
- | otherwise
- = simplRhsExpr env binder rhs new_id `thenSmpl` \ (new_rhs, arity) ->
- let
- new_id' = new_id `withArity` arity
- (new_env, new_binds') = completeBind env binder new_id' new_rhs
- in
- simplRecursiveGroup new_env new_ids pairs `thenSmpl` \ (new_pairs, final_env) ->
- returnSmpl (new_binds' ++ new_pairs, final_env)
+-- Failed try [see Note 2 above]
+-- not (isEvaldUnfolding (idUnfolding v))
+
+ = simplBinder env (zap case_bndr) `thenSmpl` \ (env, case_bndr') ->
+ returnSmpl (modifyInScope env v case_bndr', case_bndr', zap)
+ -- We could extend the substitution instead, but it would be
+ -- a hack because then the substitution wouldn't be idempotent
+ -- any more (v is an OutId). And this just just as well.
where
- ok_to_dup = switchIsSet env SimplOkToDupCode
+ zap b = b `setIdOccInfo` NoOccInfo
+
+simplCaseBinder env other_scrut case_bndr
+ = simplBinder env case_bndr `thenSmpl` \ (env, case_bndr') ->
+ returnSmpl (env, case_bndr', \ bndr -> bndr) -- NoOp on bndr
\end{code}
\begin{code}
-floatBind :: SimplEnv
- -> Bool -- True <=> Top level
- -> InBinding
- -> SmplM [InBinding]
-
-floatBind env top_level bind
- | not float_lets ||
- n_extras == 0
- = returnSmpl [bind]
-
- | otherwise
- = tickN LetFloatFromLet n_extras `thenSmpl_`
- -- It's important to increment the tick counts if we
- -- do any floating. A situation where this turns out
- -- to be important is this:
- -- Float in produces:
- -- letrec x = let y = Ey in Ex
- -- in B
- -- Now floating gives this:
- -- letrec x = Ex
- -- y = Ey
- -- in B
- --- We now want to iterate once more in case Ey doesn't
- -- mention x, in which case the y binding can be pulled
- -- out as an enclosing let(rec), which in turn gives
- -- the strictness analyser more chance.
- returnSmpl binds'
-
+simplAlts :: SimplEnv
+ -> (InId -> InId) -- Occ-info zapper
+ -> [AltCon] -- Alternatives the scrutinee can't be
+ -- in the default case
+ -> OutId -- Case binder
+ -> [InAlt] -> SimplCont
+ -> SimplM [OutAlt] -- Includes the continuation
+
+simplAlts env zap_occ_info handled_cons case_bndr' alts cont'
+ = mapSmpl simpl_alt alts
where
- binds' = fltBind bind
- n_extras = sum (map no_of_binds binds') - no_of_binds bind
-
- float_lets = switchIsSet env SimplFloatLetsExposingWHNF
- always_float_let_from_let = switchIsSet env SimplAlwaysFloatLetsFromLets
-
- -- fltBind guarantees not to return leaky floats
- -- and all the binders of the floats have had their demand-info zapped
- fltBind (NonRec bndr rhs)
- = binds ++ [NonRec bndr rhs']
- where
- (binds, rhs') = fltRhs rhs
-
- fltBind (Rec pairs)
- = [Rec pairs']
- where
- pairs' = concat [ let
- (binds, rhs') = fltRhs rhs
- in
- foldr get_pairs [(bndr, rhs')] binds
- | (bndr, rhs) <- pairs
- ]
-
- get_pairs (NonRec bndr rhs) rest = (bndr,rhs) : rest
- get_pairs (Rec pairs) rest = pairs ++ rest
-
- -- fltRhs has same invariant as fltBind
- fltRhs rhs
- | (always_float_let_from_let ||
- floatExposesHNF True False False rhs)
- = fltExpr rhs
-
- | otherwise
- = ([], rhs)
-
-
- -- fltExpr has same invariant as fltBind
- fltExpr (Let bind body)
- | not top_level || binds_wont_leak
- -- fltExpr guarantees not to return leaky floats
- = (binds' ++ body_binds, body')
- where
- binds_wont_leak = all leakFreeBind binds'
- (body_binds, body') = fltExpr body
- binds' = fltBind (un_demandify_bind bind)
-
- fltExpr expr = ([], expr)
-
--- Crude but effective
-no_of_binds (NonRec _ _) = 1
-no_of_binds (Rec pairs) = length pairs
-
-leakFreeBind (NonRec bndr rhs) = leakFree bndr rhs
-leakFreeBind (Rec pairs) = and [leakFree bndr rhs | (bndr, rhs) <- pairs]
-
-leakFree (id,_) rhs = case getIdArity id of
- ArityAtLeast n | n > 0 -> True
- ArityExactly n | n > 0 -> True
- other -> whnfOrBottom (mkFormSummary rhs)
+ inst_tys' = tyConAppArgs (idType case_bndr')
+
+ simpl_alt (DEFAULT, _, rhs)
+ = let
+ -- In the default case we record the constructors that the
+ -- case-binder *can't* be.
+ -- We take advantage of any OtherCon info in the case scrutinee
+ case_bndr_w_unf = case_bndr' `setIdUnfolding` mkOtherCon handled_cons
+ env_with_unf = modifyInScope env case_bndr' case_bndr_w_unf
+ in
+ simplExprC env_with_unf rhs cont' `thenSmpl` \ rhs' ->
+ returnSmpl (DEFAULT, [], rhs')
+
+ simpl_alt (con, vs, rhs)
+ = -- Deal with the pattern-bound variables
+ -- Mark the ones that are in ! positions in the data constructor
+ -- as certainly-evaluated.
+ -- NB: it happens that simplBinders does *not* erase the OtherCon
+ -- form of unfolding, so it's ok to add this info before
+ -- doing simplBinders
+ simplBinders env (add_evals con vs) `thenSmpl` \ (env, vs') ->
+
+ -- Bind the case-binder to (con args)
+ let
+ unfolding = mkUnfolding False (mkAltExpr con vs' inst_tys')
+ env_with_unf = modifyInScope env case_bndr' (case_bndr' `setIdUnfolding` unfolding)
+ in
+ simplExprC env_with_unf rhs cont' `thenSmpl` \ rhs' ->
+ returnSmpl (con, vs', rhs')
+
+
+ -- add_evals records the evaluated-ness of the bound variables of
+ -- a case pattern. This is *important*. Consider
+ -- data T = T !Int !Int
+ --
+ -- case x of { T a b -> T (a+1) b }
+ --
+ -- We really must record that b is already evaluated so that we don't
+ -- go and re-evaluate it when constructing the result.
+
+ add_evals (DataAlt dc) vs = cat_evals vs (dataConRepStrictness dc)
+ add_evals other_con vs = vs
+
+ cat_evals [] [] = []
+ cat_evals (v:vs) (str:strs)
+ | isTyVar v = v : cat_evals vs (str:strs)
+ | isMarkedStrict str = evald_v : cat_evals vs strs
+ | otherwise = zapped_v : cat_evals vs strs
+ where
+ zapped_v = zap_occ_info v
+ evald_v = zapped_v `setIdUnfolding` mkOtherCon []
\end{code}
%************************************************************************
%* *
-\subsection[Simplify-atoms]{Simplifying atoms}
+\subsection{Known constructor}
%* *
%************************************************************************
+We are a bit careful with occurrence info. Here's an example
+
+ (\x* -> case x of (a*, b) -> f a) (h v, e)
+
+where the * means "occurs once". This effectively becomes
+ case (h v, e) of (a*, b) -> f a)
+and then
+ let a* = h v; b = e in f a
+and then
+ f (h v)
+
+All this should happen in one sweep.
+
\begin{code}
-simplArg :: SimplEnv -> InArg -> Eager ans OutArg
-
-simplArg env (LitArg lit) = returnEager (LitArg lit)
-simplArg env (TyArg ty) = simplTy env ty `appEager` \ ty' ->
- returnEager (TyArg ty')
-simplArg env arg@(VarArg id)
- = case lookupIdSubst env id of
- Just (SubstVar id') -> returnEager (VarArg id')
- Just (SubstLit lit) -> returnEager (LitArg lit)
- Just (SubstExpr _ __) -> panic "simplArg"
- Nothing -> case lookupOutIdEnv env id of
- Just (id', _, _) -> returnEager (VarArg id')
- Nothing -> returnEager arg
+knownCon :: SimplEnv -> AltCon -> [OutExpr]
+ -> InId -> [InAlt] -> SimplCont
+ -> SimplM FloatsWithExpr
+
+knownCon env con args bndr alts cont
+ = tick (KnownBranch bndr) `thenSmpl_`
+ case findAlt con alts of
+ (DEFAULT, bs, rhs) -> ASSERT( null bs )
+ simplNonRecX env bndr scrut $ \ env ->
+ -- This might give rise to a binding with non-atomic args
+ -- like x = Node (f x) (g x)
+ -- but no harm will be done
+ simplExprF env rhs cont
+ where
+ scrut = case con of
+ LitAlt lit -> Lit lit
+ DataAlt dc -> mkConApp dc args
+
+ (LitAlt lit, bs, rhs) -> ASSERT( null bs )
+ simplNonRecX env bndr (Lit lit) $ \ env ->
+ simplExprF env rhs cont
+
+ (DataAlt dc, bs, rhs) -> ASSERT( length bs + n_tys == length args )
+ bind_args env bs (drop n_tys args) $ \ env ->
+ let
+ con_app = mkConApp dc (take n_tys args ++ con_args)
+ con_args = [substExpr (getSubst env) (varToCoreExpr b) | b <- bs]
+ -- args are aready OutExprs, but bs are InIds
+ in
+ simplNonRecX env bndr con_app $ \ env ->
+ simplExprF env rhs cont
+ where
+ n_tys = dataConNumInstArgs dc -- Non-existential type args
+-- Ugh!
+bind_args env [] _ thing_inside = thing_inside env
+
+bind_args env (b:bs) (Type ty : args) thing_inside
+ = bind_args (extendSubst env b (DoneTy ty)) bs args thing_inside
+
+bind_args env (b:bs) (arg : args) thing_inside
+ = simplNonRecX env b arg $ \ env ->
+ bind_args env bs args thing_inside
\end{code}
+
%************************************************************************
%* *
-\subsection[Simplify-quickies]{Some local help functions}
+\subsection{Duplicating continuations}
%* *
%************************************************************************
-
\begin{code}
--- un_demandify_bind switches off the willBeDemanded Info field
--- for bindings floated out of a non-demanded let
-un_demandify_bind (NonRec binder rhs)
- = NonRec (un_demandify_bndr binder) rhs
-un_demandify_bind (Rec pairs)
- = Rec [(un_demandify_bndr binder, rhs) | (binder,rhs) <- pairs]
-
-un_demandify_bndr (id, occ_info) = (id `addIdDemandInfo` noDemandInfo, occ_info)
-
-is_cheap_prim_app (Prim op _) = primOpOkForSpeculation op
-is_cheap_prim_app other = False
+prepareCaseCont :: SimplEnv
+ -> [InAlt] -> SimplCont
+ -> SimplM (FloatsWith (SimplCont,SimplCont))
+ -- Return a duplicatable continuation, a non-duplicable part
+ -- plus some extra bindings
+
+ -- No need to make it duplicatable if there's only one alternative
+prepareCaseCont env [alt] cont = returnSmpl (emptyFloats env, (cont, mkBoringStop (contResultType cont)))
+prepareCaseCont env alts cont = mkDupableCont env cont
+\end{code}
-computeResultType :: SimplEnv -> InType -> [OutArg] -> OutType
-computeResultType env expr_ty orig_args
- = simplTy env expr_ty `appEager` \ expr_ty' ->
+\begin{code}
+mkDupableCont :: SimplEnv -> SimplCont
+ -> SimplM (FloatsWith (SimplCont, SimplCont))
+
+mkDupableCont env cont
+ | contIsDupable cont
+ = returnSmpl (emptyFloats env, (cont, mkBoringStop (contResultType cont)))
+
+mkDupableCont env (CoerceIt ty cont)
+ = mkDupableCont env cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
+ returnSmpl (floats, (CoerceIt ty dup_cont, nondup_cont))
+
+mkDupableCont env (InlinePlease cont)
+ = mkDupableCont env cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
+ returnSmpl (floats, (InlinePlease dup_cont, nondup_cont))
+
+mkDupableCont env cont@(ArgOf _ arg_ty _ _)
+ = returnSmpl (emptyFloats env, (mkBoringStop arg_ty, cont))
+ -- Do *not* duplicate an ArgOf continuation
+ -- Because ArgOf continuations are opaque, we gain nothing by
+ -- propagating them into the expressions, and we do lose a lot.
+ -- Here's an example:
+ -- && (case x of { T -> F; F -> T }) E
+ -- Now, && is strict so we end up simplifying the case with
+ -- an ArgOf continuation. If we let-bind it, we get
+ --
+ -- let $j = \v -> && v E
+ -- in simplExpr (case x of { T -> F; F -> T })
+ -- (ArgOf (\r -> $j r)
+ -- And after simplifying more we get
+ --
+ -- let $j = \v -> && v E
+ -- in case of { T -> $j F; F -> $j T }
+ -- Which is a Very Bad Thing
+ --
+ -- The desire not to duplicate is the entire reason that
+ -- mkDupableCont returns a pair of continuations.
+ --
+ -- The original plan had:
+ -- e.g. (...strict-fn...) [...hole...]
+ -- ==>
+ -- let $j = \a -> ...strict-fn...
+ -- in $j [...hole...]
+
+mkDupableCont env (ApplyTo _ arg se cont)
+ = -- e.g. [...hole...] (...arg...)
+ -- ==>
+ -- let a = ...arg...
+ -- in [...hole...] a
+ simplExpr (setInScope se env) arg `thenSmpl` \ arg' ->
+
+ mkDupableCont env cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
+ addFloats env floats $ \ env ->
+
+ if exprIsDupable arg' then
+ returnSmpl (emptyFloats env, (ApplyTo OkToDup arg' (zapSubstEnv se) dup_cont, nondup_cont))
+ else
+ newId FSLIT("a") (exprType arg') `thenSmpl` \ arg_id ->
+
+ tick (CaseOfCase arg_id) `thenSmpl_`
+ -- Want to tick here so that we go round again,
+ -- and maybe copy or inline the code.
+ -- Not strictly CaseOfCase, but never mind
+
+ returnSmpl (unitFloat env arg_id arg',
+ (ApplyTo OkToDup (Var arg_id) (zapSubstEnv se) dup_cont,
+ nondup_cont))
+ -- But what if the arg should be case-bound?
+ -- This has been this way for a long time, so I'll leave it,
+ -- but I can't convince myself that it's right.
+
+
+mkDupableCont env (Select _ case_bndr alts se cont)
+ = -- e.g. (case [...hole...] of { pi -> ei })
+ -- ===>
+ -- let ji = \xij -> ei
+ -- in case [...hole...] of { pi -> ji xij }
+ tick (CaseOfCase case_bndr) `thenSmpl_`
let
- go ty [] = ty
- go ty (TyArg ty_arg : args) = go (mkAppTy ty ty_arg) args
- go ty (a:args) | isValArg a = case (splitFunTy_maybe ty) of
- Just (_, res_ty) -> go res_ty args
- Nothing ->
- pprPanic "computeResultType" (vcat [
- ppr (a:args),
- ppr orig_args,
- ppr expr_ty',
- ppr ty])
+ alt_env = setInScope se env
in
- go expr_ty' orig_args
-
-
-var `withArity` UnknownArity = var
-var `withArity` arity = var `addIdArity` arity
-
-is_atomic (Var v) = True
-is_atomic (Lit l) = not (isNoRepLit l)
-is_atomic other = False
+ prepareCaseCont alt_env alts cont `thenSmpl` \ (floats1, (dup_cont, nondup_cont)) ->
+ addFloats alt_env floats1 $ \ alt_env ->
+
+ simplBinder alt_env case_bndr `thenSmpl` \ (alt_env, case_bndr') ->
+ -- NB: simplBinder does not zap deadness occ-info, so
+ -- a dead case_bndr' will still advertise its deadness
+ -- This is really important because in
+ -- case e of b { (# a,b #) -> ... }
+ -- b is always dead, and indeed we are not allowed to bind b to (# a,b #),
+ -- which might happen if e was an explicit unboxed pair and b wasn't marked dead.
+ -- In the new alts we build, we have the new case binder, so it must retain
+ -- its deadness.
+
+ mkDupableAlts alt_env case_bndr' alts dup_cont `thenSmpl` \ (floats2, alts') ->
+ addFloats alt_env floats2 $ \ alt_env ->
+ returnSmpl (emptyFloats alt_env,
+ (Select OkToDup case_bndr' alts' (zapSubstEnv se)
+ (mkBoringStop (contResultType dup_cont)),
+ nondup_cont))
+
+mkDupableAlts :: SimplEnv -> OutId -> [InAlt] -> SimplCont
+ -> SimplM (FloatsWith [InAlt])
+-- Absorbs the continuation into the new alternatives
+
+mkDupableAlts env case_bndr' alts dupable_cont
+ = go env alts
+ where
+ go env [] = returnSmpl (emptyFloats env, [])
+ go env (alt:alts)
+ = mkDupableAlt env case_bndr' dupable_cont alt `thenSmpl` \ (floats1, alt') ->
+ addFloats env floats1 $ \ env ->
+ go env alts `thenSmpl` \ (floats2, alts') ->
+ returnSmpl (floats2, alt' : alts')
+
+mkDupableAlt env case_bndr' cont alt@(con, bndrs, rhs)
+ = simplBinders env bndrs `thenSmpl` \ (env, bndrs') ->
+ simplExprC env rhs cont `thenSmpl` \ rhs' ->
+
+ if exprIsDupable rhs' then
+ returnSmpl (emptyFloats env, (con, bndrs', rhs'))
+ -- It is worth checking for a small RHS because otherwise we
+ -- get extra let bindings that may cause an extra iteration of the simplifier to
+ -- inline back in place. Quite often the rhs is just a variable or constructor.
+ -- The Ord instance of Maybe in PrelMaybe.lhs, for example, took several extra
+ -- iterations because the version with the let bindings looked big, and so wasn't
+ -- inlined, but after the join points had been inlined it looked smaller, and so
+ -- was inlined.
+ --
+ -- NB: we have to check the size of rhs', not rhs.
+ -- Duplicating a small InAlt might invalidate occurrence information
+ -- However, if it *is* dupable, we return the *un* simplified alternative,
+ -- because otherwise we'd need to pair it up with an empty subst-env....
+ -- but we only have one env shared between all the alts.
+ -- (Remember we must zap the subst-env before re-simplifying something).
+ -- Rather than do this we simply agree to re-simplify the original (small) thing later.
+
+ else
+ let
+ rhs_ty' = exprType rhs'
+ used_bndrs' = filter (not . isDeadBinder) (case_bndr' : bndrs')
+ -- The deadness info on the new binders is unscathed
+ in
+ -- If we try to lift a primitive-typed something out
+ -- for let-binding-purposes, we will *caseify* it (!),
+ -- with potentially-disastrous strictness results. So
+ -- instead we turn it into a function: \v -> e
+ -- where v::State# RealWorld#. The value passed to this function
+ -- is realworld#, which generates (almost) no code.
+
+ -- There's a slight infelicity here: we pass the overall
+ -- case_bndr to all the join points if it's used in *any* RHS,
+ -- because we don't know its usage in each RHS separately
+
+ -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
+ -- we make the join point into a function whenever used_bndrs'
+ -- is empty. This makes the join-point more CPR friendly.
+ -- Consider: let j = if .. then I# 3 else I# 4
+ -- in case .. of { A -> j; B -> j; C -> ... }
+ --
+ -- Now CPR doesn't w/w j because it's a thunk, so
+ -- that means that the enclosing function can't w/w either,
+ -- which is a lose. Here's the example that happened in practice:
+ -- kgmod :: Int -> Int -> Int
+ -- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
+ -- then 78
+ -- else 5
+ --
+ -- I have seen a case alternative like this:
+ -- True -> \v -> ...
+ -- It's a bit silly to add the realWorld dummy arg in this case, making
+ -- $j = \s v -> ...
+ -- True -> $j s
+ -- (the \v alone is enough to make CPR happy) but I think it's rare
+
+ ( if null used_bndrs'
+ then newId FSLIT("w") realWorldStatePrimTy `thenSmpl` \ rw_id ->
+ returnSmpl ([rw_id], [Var realWorldPrimId])
+ else
+ returnSmpl (used_bndrs', map varToCoreExpr used_bndrs')
+ ) `thenSmpl` \ (final_bndrs', final_args) ->
+
+ -- See comment about "$j" name above
+ newId (encodeFS SLIT("$j")) (mkPiTypes final_bndrs' rhs_ty') `thenSmpl` \ join_bndr ->
+ -- Notice the funky mkPiTypes. If the contructor has existentials
+ -- it's possible that the join point will be abstracted over
+ -- type varaibles as well as term variables.
+ -- Example: Suppose we have
+ -- data T = forall t. C [t]
+ -- Then faced with
+ -- case (case e of ...) of
+ -- C t xs::[t] -> rhs
+ -- We get the join point
+ -- let j :: forall t. [t] -> ...
+ -- j = /\t \xs::[t] -> rhs
+ -- in
+ -- case (case e of ...) of
+ -- C t xs::[t] -> j t xs
+ let
+ -- We make the lambdas into one-shot-lambdas. The
+ -- join point is sure to be applied at most once, and doing so
+ -- prevents the body of the join point being floated out by
+ -- the full laziness pass
+ really_final_bndrs = map one_shot final_bndrs'
+ one_shot v | isId v = setOneShotLambda v
+ | otherwise = v
+ join_rhs = mkLams really_final_bndrs rhs'
+ join_call = mkApps (Var join_bndr) final_args
+ in
+ returnSmpl (unitFloat env join_bndr join_rhs, (con, bndrs', join_call))
\end{code}
-
projects / ghc-hetmet.git / blobdiff