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| author | Ian Lynagh <ian@well-typed.com> | 2012-10-09 22:24:49 +0100 |
|---|---|---|
| committer | Ian Lynagh <ian@well-typed.com> | 2012-10-09 22:24:49 +0100 |
| commit | d131d66efe4595981f46e10171ba75be1cb53bb0 (patch) | |
| tree | b68685cc2eb8fe483ca17a88b6b279da2b1bb4fa | |
| parent | 577f50f10ede3907d35395d02fb8d11d6c26aa17 (diff) | |
| download | haskell-d131d66efe4595981f46e10171ba75be1cb53bb0.tar.gz | |
Whitespace only in simplCore/SimplUtils.lhs
| -rw-r--r-- | compiler/simplCore/SimplUtils.lhs | 1115 |
1 files changed, 554 insertions, 561 deletions
diff --git a/compiler/simplCore/SimplUtils.lhs b/compiler/simplCore/SimplUtils.lhs index a5ed3976bd..54256498eb 100644 --- a/compiler/simplCore/SimplUtils.lhs +++ b/compiler/simplCore/SimplUtils.lhs @@ -4,35 +4,28 @@ \section[SimplUtils]{The simplifier utilities} \begin{code} -{-# OPTIONS -fno-warn-tabs #-} --- The above warning supression flag is a temporary kludge. --- While working on this module you are encouraged to remove it and --- detab the module (please do the detabbing in a separate patch). See --- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#TabsvsSpaces --- for details - module SimplUtils ( - -- Rebuilding - mkLam, mkCase, prepareAlts, tryEtaExpand, + -- Rebuilding + mkLam, mkCase, prepareAlts, tryEtaExpand, - -- Inlining, - preInlineUnconditionally, postInlineUnconditionally, - activeUnfolding, activeRule, - getUnfoldingInRuleMatch, + -- Inlining, + preInlineUnconditionally, postInlineUnconditionally, + activeUnfolding, activeRule, + getUnfoldingInRuleMatch, simplEnvForGHCi, updModeForInlineRules, - -- The continuation type - SimplCont(..), DupFlag(..), ArgInfo(..), + -- The continuation type + SimplCont(..), DupFlag(..), ArgInfo(..), isSimplified, - contIsDupable, contResultType, contInputType, - contIsTrivial, contArgs, dropArgs, - pushSimplifiedArgs, countValArgs, countArgs, addArgTo, - mkBoringStop, mkRhsStop, mkLazyArgStop, contIsRhsOrArg, - interestingCallContext, - - interestingArg, mkArgInfo, - - abstractFloats + contIsDupable, contResultType, contInputType, + contIsTrivial, contArgs, dropArgs, + pushSimplifiedArgs, countValArgs, countArgs, addArgTo, + mkBoringStop, mkRhsStop, mkLazyArgStop, contIsRhsOrArg, + interestingCallContext, + + interestingArg, mkArgInfo, + + abstractFloats ) where #include "HsVersions.h" @@ -54,7 +47,7 @@ import Id import Var import Demand import SimplMonad -import Type hiding( substTy ) +import Type hiding( substTy ) import Coercion hiding( substCo, substTy ) import DataCon ( dataConWorkId ) import VarSet @@ -70,12 +63,12 @@ import Control.Monad ( when ) %************************************************************************ -%* * - The SimplCont type -%* * +%* * + The SimplCont type +%* * %************************************************************************ -A SimplCont allows the simplifier to traverse the expression in a +A SimplCont allows the simplifier to traverse the expression in a zipper-like fashion. The SimplCont represents the rest of the expression, "above" the point of interest. @@ -83,55 +76,55 @@ You can also think of a SimplCont as an "evaluation context", using that term in the way it is used for operational semantics. This is the way I usually think of it, For example you'll often see a syntax for evaluation context looking like - C ::= [] | C e | case C of alts | C `cast` co + C ::= [] | C e | case C of alts | C `cast` co That's the kind of thing we are doing here, and I use that syntax in the comments. Key points: - * A SimplCont describes a *strict* context (just like + * A SimplCont describes a *strict* context (just like evaluation contexts do). E.g. Just [] is not a SimplCont * A SimplCont describes a context that *does not* bind any variables. E.g. \x. [] is not a SimplCont \begin{code} -data SimplCont - = Stop -- An empty context, or <hole> +data SimplCont + = Stop -- An empty context, or <hole> OutType -- Type of the <hole> - CallCtxt -- True <=> There is something interesting about - -- the context, and hence the inliner - -- should be a bit keener (see interestingCallContext) - -- Specifically: - -- This is an argument of a function that has RULES - -- Inlining the call might allow the rule to fire - - | CoerceIt -- <hole> `cast` co - OutCoercion -- The coercion simplified - -- Invariant: never an identity coercion - SimplCont - - | ApplyTo -- <hole> arg - DupFlag -- See Note [DupFlag invariants] - InExpr StaticEnv -- The argument and its static env - SimplCont - - | Select -- case <hole> of alts - DupFlag -- See Note [DupFlag invariants] - InId [InAlt] StaticEnv -- The case binder, alts type, alts, and subst-env - SimplCont + CallCtxt -- True <=> There is something interesting about + -- the context, and hence the inliner + -- should be a bit keener (see interestingCallContext) + -- Specifically: + -- This is an argument of a function that has RULES + -- Inlining the call might allow the rule to fire + + | CoerceIt -- <hole> `cast` co + OutCoercion -- The coercion simplified + -- Invariant: never an identity coercion + SimplCont + + | ApplyTo -- <hole> arg + DupFlag -- See Note [DupFlag invariants] + InExpr StaticEnv -- The argument and its static env + SimplCont + + | Select -- case <hole> of alts + DupFlag -- See Note [DupFlag invariants] + InId [InAlt] StaticEnv -- The case binder, alts type, alts, and subst-env + SimplCont -- The two strict forms have no DupFlag, because we never duplicate them - | StrictBind -- (\x* \xs. e) <hole> - InId [InBndr] -- let x* = <hole> in e - InExpr StaticEnv -- is a special case - SimplCont - - | StrictArg -- f e1 ..en <hole> - ArgInfo -- Specifies f, e1..en, Whether f has rules, etc - -- plus strictness flags for *further* args + | StrictBind -- (\x* \xs. e) <hole> + InId [InBndr] -- let x* = <hole> in e + InExpr StaticEnv -- is a special case + SimplCont + + | StrictArg -- f e1 ..en <hole> + ArgInfo -- Specifies f, e1..en, Whether f has rules, etc + -- plus strictness flags for *further* args CallCtxt -- Whether *this* argument position is interesting - SimplCont + SimplCont | TickIt (Tickish Id) -- Tick tickish <hole> @@ -139,22 +132,22 @@ data SimplCont data ArgInfo = ArgInfo { - ai_fun :: OutId, -- The function - ai_args :: [OutExpr], -- ...applied to these args (which are in *reverse* order) + ai_fun :: OutId, -- The function + ai_args :: [OutExpr], -- ...applied to these args (which are in *reverse* order) ai_type :: OutType, -- Type of (f a1 ... an) - ai_rules :: [CoreRule], -- Rules for this function - - ai_encl :: Bool, -- Flag saying whether this function - -- or an enclosing one has rules (recursively) - -- True => be keener to inline in all args - - ai_strs :: [Bool], -- Strictness of remaining arguments - -- Usually infinite, but if it is finite it guarantees - -- that the function diverges after being given - -- that number of args - ai_discs :: [Int] -- Discounts for remaining arguments; non-zero => be keener to inline - -- Always infinite + ai_rules :: [CoreRule], -- Rules for this function + + ai_encl :: Bool, -- Flag saying whether this function + -- or an enclosing one has rules (recursively) + -- True => be keener to inline in all args + + ai_strs :: [Bool], -- Strictness of remaining arguments + -- Usually infinite, but if it is finite it guarantees + -- that the function diverges after being given + -- that number of args + ai_discs :: [Int] -- Discounts for remaining arguments; non-zero => be keener to inline + -- Always infinite } addArgTo :: ArgInfo -> OutExpr -> ArgInfo @@ -162,14 +155,14 @@ addArgTo ai arg = ai { ai_args = arg : ai_args ai , ai_type = applyTypeToArg (ai_type ai) arg } instance Outputable SimplCont where - ppr (Stop ty interesting) = ptext (sLit "Stop") <> brackets (ppr interesting) <+> ppr ty + ppr (Stop ty interesting) = ptext (sLit "Stop") <> brackets (ppr interesting) <+> ppr ty ppr (ApplyTo dup arg _ cont) = ((ptext (sLit "ApplyTo") <+> ppr dup <+> pprParendExpr arg) - {- $$ nest 2 (pprSimplEnv se) -}) $$ ppr cont + {- $$ nest 2 (pprSimplEnv se) -}) $$ ppr cont ppr (StrictBind b _ _ _ cont) = (ptext (sLit "StrictBind") <+> ppr b) $$ ppr cont ppr (StrictArg ai _ cont) = (ptext (sLit "StrictArg") <+> ppr (ai_fun ai)) $$ ppr cont - ppr (Select dup bndr alts se cont) = (ptext (sLit "Select") <+> ppr dup <+> ppr bndr) $$ - (nest 2 $ vcat [ppr (seTvSubst se), ppr alts]) $$ ppr cont - ppr (CoerceIt co cont) = (ptext (sLit "CoerceIt") <+> ppr co) $$ ppr cont + ppr (Select dup bndr alts se cont) = (ptext (sLit "Select") <+> ppr dup <+> ppr bndr) $$ + (nest 2 $ vcat [ppr (seTvSubst se), ppr alts]) $$ ppr cont + ppr (CoerceIt co cont) = (ptext (sLit "CoerceIt") <+> ppr co) $$ ppr cont ppr (TickIt t cont) = (ptext (sLit "TickIt") <+> ppr t) $$ ppr cont data DupFlag = NoDup -- Unsimplified, might be big @@ -178,7 +171,7 @@ data DupFlag = NoDup -- Unsimplified, might be big isSimplified :: DupFlag -> Bool isSimplified NoDup = False -isSimplified _ = True -- Invariant: the subst-env is empty +isSimplified _ = True -- Invariant: the subst-env is empty instance Outputable DupFlag where ppr OkToDup = ptext (sLit "ok") @@ -201,7 +194,7 @@ the following invariants hold mkBoringStop :: OutType -> SimplCont mkBoringStop ty = Stop ty BoringCtxt -mkRhsStop :: OutType -> SimplCont -- See Note [RHS of lets] in CoreUnfold +mkRhsStop :: OutType -> SimplCont -- See Note [RHS of lets] in CoreUnfold mkRhsStop ty = Stop ty (ArgCtxt False) mkLazyArgStop :: OutType -> CallCtxt -> SimplCont @@ -217,7 +210,7 @@ contIsRhsOrArg _ = False ------------------- contIsDupable :: SimplCont -> Bool contIsDupable (Stop {}) = True -contIsDupable (ApplyTo OkToDup _ _ _) = True -- See Note [DupFlag invariants] +contIsDupable (ApplyTo OkToDup _ _ _) = True -- See Note [DupFlag invariants] contIsDupable (Select OkToDup _ _ _ _) = True -- ...ditto... contIsDupable (CoerceIt _ cont) = contIsDupable cont contIsDupable _ = False @@ -250,7 +243,7 @@ contInputType (ApplyTo d e se k) = mkFunTy (perhapsSubstTy d se (exprType e contInputType (TickIt _ k) = contInputType k perhapsSubstTy :: DupFlag -> SimplEnv -> InType -> OutType -perhapsSubstTy dup_flag se ty +perhapsSubstTy dup_flag se ty | isSimplified dup_flag = ty | otherwise = substTy se ty @@ -276,20 +269,20 @@ contArgs cont@(ApplyTo {}) go args cont = (reverse args, cont) is_interesting arg se = interestingArg (substExpr (text "contArgs") se arg) - -- Do *not* use short-cutting substitution here - -- because we want to get as much IdInfo as possible + -- Do *not* use short-cutting substitution here + -- because we want to get as much IdInfo as possible contArgs cont = (True, [], cont) pushSimplifiedArgs :: SimplEnv -> [CoreExpr] -> SimplCont -> SimplCont pushSimplifiedArgs _env [] cont = cont pushSimplifiedArgs env (arg:args) cont = ApplyTo Simplified arg env (pushSimplifiedArgs env args cont) - -- The env has an empty SubstEnv + -- The env has an empty SubstEnv dropArgs :: Int -> SimplCont -> SimplCont dropArgs 0 cont = cont dropArgs n (ApplyTo _ _ _ cont) = dropArgs (n-1) cont -dropArgs n other = pprPanic "dropArgs" (ppr n <+> ppr other) +dropArgs n other = pprPanic "dropArgs" (ppr n <+> ppr other) \end{code} @@ -298,14 +291,14 @@ Note [Interesting call context] We want to avoid inlining an expression where there can't possibly be any gain, such as in an argument position. Hence, if the continuation is interesting (eg. a case scrutinee, application etc.) then we -inline, otherwise we don't. +inline, otherwise we don't. Previously some_benefit used to return True only if the variable was applied to some value arguments. This didn't work: - let x = _coerce_ (T Int) Int (I# 3) in - case _coerce_ Int (T Int) x of - I# y -> .... + let x = _coerce_ (T Int) Int (I# 3) in + case _coerce_ Int (T Int) x of + I# y -> .... we want to inline x, but can't see that it's a constructor in a case scrutinee position, and some_benefit is False. @@ -319,7 +312,7 @@ dMonadST = _/\_ t -> :Monad (g1 _@_ t, g2 _@_ t, g3 _@_ t) we'd really like to inline dMonadST here, but we *don't* want to inline if the case expression is just - case x of y { DEFAULT -> ... } + case x of y { DEFAULT -> ... } since we can just eliminate this case instead (x is in WHNF). Similar applies when x is bound to a lambda expression. Hence @@ -334,113 +327,113 @@ interestingCallContext cont = interesting cont where interesting (Select _ bndr _ _ _) - | isDeadBinder bndr = CaseCtxt - | otherwise = ArgCtxt False -- If the binder is used, this - -- is like a strict let - -- See Note [RHS of lets] in CoreUnfold - + | isDeadBinder bndr = CaseCtxt + | otherwise = ArgCtxt False -- If the binder is used, this + -- is like a strict let + -- See Note [RHS of lets] in CoreUnfold + interesting (ApplyTo _ arg _ cont) - | isTypeArg arg = interesting cont - | otherwise = ValAppCtxt -- Can happen if we have (f Int |> co) y - -- If f has an INLINE prag we need to give it some - -- motivation to inline. See Note [Cast then apply] - -- in CoreUnfold + | isTypeArg arg = interesting cont + | otherwise = ValAppCtxt -- Can happen if we have (f Int |> co) y + -- If f has an INLINE prag we need to give it some + -- motivation to inline. See Note [Cast then apply] + -- in CoreUnfold interesting (StrictArg _ cci _) = cci - interesting (StrictBind {}) = BoringCtxt - interesting (Stop _ cci) = cci + interesting (StrictBind {}) = BoringCtxt + interesting (Stop _ cci) = cci interesting (TickIt _ cci) = interesting cci interesting (CoerceIt _ cont) = interesting cont - -- If this call is the arg of a strict function, the context - -- is a bit interesting. If we inline here, we may get useful - -- evaluation information to avoid repeated evals: e.g. - -- x + (y * z) - -- Here the contIsInteresting makes the '*' keener to inline, - -- which in turn exposes a constructor which makes the '+' inline. - -- Assuming that +,* aren't small enough to inline regardless. - -- - -- It's also very important to inline in a strict context for things - -- like - -- foldr k z (f x) - -- Here, the context of (f x) is strict, and if f's unfolding is - -- a build it's *great* to inline it here. So we must ensure that - -- the context for (f x) is not totally uninteresting. + -- If this call is the arg of a strict function, the context + -- is a bit interesting. If we inline here, we may get useful + -- evaluation information to avoid repeated evals: e.g. + -- x + (y * z) + -- Here the contIsInteresting makes the '*' keener to inline, + -- which in turn exposes a constructor which makes the '+' inline. + -- Assuming that +,* aren't small enough to inline regardless. + -- + -- It's also very important to inline in a strict context for things + -- like + -- foldr k z (f x) + -- Here, the context of (f x) is strict, and if f's unfolding is + -- a build it's *great* to inline it here. So we must ensure that + -- the context for (f x) is not totally uninteresting. ------------------- mkArgInfo :: Id - -> [CoreRule] -- Rules for function - -> Int -- Number of value args - -> SimplCont -- Context of the call - -> ArgInfo + -> [CoreRule] -- Rules for function + -> Int -- Number of value args + -> SimplCont -- Context of the call + -> ArgInfo mkArgInfo fun rules n_val_args call_cont - | n_val_args < idArity fun -- Note [Unsaturated functions] + | n_val_args < idArity fun -- Note [Unsaturated functions] = ArgInfo { ai_fun = fun, ai_args = [], ai_type = fun_ty , ai_rules = rules, ai_encl = False - , ai_strs = vanilla_stricts - , ai_discs = vanilla_discounts } + , ai_strs = vanilla_stricts + , ai_discs = vanilla_discounts } | otherwise = ArgInfo { ai_fun = fun, ai_args = [], ai_type = fun_ty , ai_rules = rules , ai_encl = interestingArgContext rules call_cont - , ai_strs = add_type_str fun_ty arg_stricts - , ai_discs = arg_discounts } + , ai_strs = add_type_str fun_ty arg_stricts + , ai_discs = arg_discounts } where fun_ty = idType fun vanilla_discounts, arg_discounts :: [Int] vanilla_discounts = repeat 0 arg_discounts = case idUnfolding fun of - CoreUnfolding {uf_guidance = UnfIfGoodArgs {ug_args = discounts}} - -> discounts ++ vanilla_discounts - _ -> vanilla_discounts + CoreUnfolding {uf_guidance = UnfIfGoodArgs {ug_args = discounts}} + -> discounts ++ vanilla_discounts + _ -> vanilla_discounts vanilla_stricts, arg_stricts :: [Bool] vanilla_stricts = repeat False arg_stricts = case splitStrictSig (idStrictness fun) of - (demands, result_info) - | not (demands `lengthExceeds` n_val_args) - -> -- Enough args, use the strictness given. - -- For bottoming functions we used to pretend that the arg - -- is lazy, so that we don't treat the arg as an - -- interesting context. This avoids substituting - -- top-level bindings for (say) strings into - -- calls to error. But now we are more careful about - -- inlining lone variables, so its ok (see SimplUtils.analyseCont) - if isBotRes result_info then - map isStrictDmd demands -- Finite => result is bottom - else - map isStrictDmd demands ++ vanilla_stricts - | otherwise - -> WARN( True, text "More demands than arity" <+> ppr fun <+> ppr (idArity fun) - <+> ppr n_val_args <+> ppr demands ) - vanilla_stricts -- Not enough args, or no strictness + (demands, result_info) + | not (demands `lengthExceeds` n_val_args) + -> -- Enough args, use the strictness given. + -- For bottoming functions we used to pretend that the arg + -- is lazy, so that we don't treat the arg as an + -- interesting context. This avoids substituting + -- top-level bindings for (say) strings into + -- calls to error. But now we are more careful about + -- inlining lone variables, so its ok (see SimplUtils.analyseCont) + if isBotRes result_info then + map isStrictDmd demands -- Finite => result is bottom + else + map isStrictDmd demands ++ vanilla_stricts + | otherwise + -> WARN( True, text "More demands than arity" <+> ppr fun <+> ppr (idArity fun) + <+> ppr n_val_args <+> ppr demands ) + vanilla_stricts -- Not enough args, or no strictness add_type_str :: Type -> [Bool] -> [Bool] -- If the function arg types are strict, record that in the 'strictness bits' -- No need to instantiate because unboxed types (which dominate the strict -- types) can't instantiate type variables. - -- add_type_str is done repeatedly (for each call); might be better + -- add_type_str is done repeatedly (for each call); might be better -- once-for-all in the function -- But beware primops/datacons with no strictness add_type_str _ [] = [] - add_type_str fun_ty strs -- Look through foralls - | Just (_, fun_ty') <- splitForAllTy_maybe fun_ty -- Includes coercions - = add_type_str fun_ty' strs - add_type_str fun_ty (str:strs) -- Add strict-type info - | Just (arg_ty, fun_ty') <- splitFunTy_maybe fun_ty - = (str || isStrictType arg_ty) : add_type_str fun_ty' strs + add_type_str fun_ty strs -- Look through foralls + | Just (_, fun_ty') <- splitForAllTy_maybe fun_ty -- Includes coercions + = add_type_str fun_ty' strs + add_type_str fun_ty (str:strs) -- Add strict-type info + | Just (arg_ty, fun_ty') <- splitFunTy_maybe fun_ty + = (str || isStrictType arg_ty) : add_type_str fun_ty' strs add_type_str _ strs - = strs + = strs {- Note [Unsaturated functions] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider (test eyeball/inline4) - x = a:as - y = f x + x = a:as + y = f x where f has arity 2. Then we do not want to inline 'x', because it'll just be floated out again. Even if f has lots of discounts on its first argument -- it must be saturated for these to kick in @@ -450,15 +443,15 @@ interestingArgContext :: [CoreRule] -> SimplCont -> Bool -- If the argument has form (f x y), where x,y are boring, -- and f is marked INLINE, then we don't want to inline f. -- But if the context of the argument is --- g (f x y) +-- g (f x y) -- where g has rules, then we *do* want to inline f, in case it -- exposes a rule that might fire. Similarly, if the context is --- h (g (f x x)) +-- h (g (f x x)) -- where h has rules, then we do want to inline f; hence the -- call_cont argument to interestingArgContext -- -- The ai-rules flag makes this happen; if it's --- set, the inliner gets just enough keener to inline f +-- set, the inliner gets just enough keener to inline f -- regardless of how boring f's arguments are, if it's marked INLINE -- -- The alternative would be to *always* inline an INLINE function, @@ -469,11 +462,11 @@ interestingArgContext rules call_cont where enclosing_fn_has_rules = go call_cont - go (Select {}) = False - go (ApplyTo {}) = False + go (Select {}) = False + go (ApplyTo {}) = False go (StrictArg _ cci _) = interesting cci - go (StrictBind {}) = False -- ?? - go (CoerceIt _ c) = go c + go (StrictBind {}) = False -- ?? + go (CoerceIt _ c) = go c go (Stop _ cci) = interesting cci go (TickIt _ c) = go c @@ -483,9 +476,9 @@ interestingArgContext rules call_cont %************************************************************************ -%* * +%* * SimplifierMode -%* * +%* * %************************************************************************ The SimplifierMode controls several switches; see its definition in @@ -516,8 +509,8 @@ updModeForInlineRules inline_rule_act current_mode = current_mode { sm_phase = phaseFromActivation inline_rule_act , sm_inline = True , sm_eta_expand = False } - -- For sm_rules, just inherit; sm_rules might be "off" - -- becuase of -fno-enable-rewrite-rules + -- For sm_rules, just inherit; sm_rules might be "off" + -- becuase of -fno-enable-rewrite-rules where phaseFromActivation (ActiveAfter n) = Phase n phaseFromActivation _ = InitialPhase @@ -525,21 +518,21 @@ updModeForInlineRules inline_rule_act current_mode Note [Inlining in gentle mode] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -Something is inlined if +Something is inlined if (i) the sm_inline flag is on, AND (ii) the thing has an INLINE pragma, AND - (iii) the thing is inlinable in the earliest phase. + (iii) the thing is inlinable in the earliest phase. Example of why (iii) is important: {-# INLINE [~1] g #-} g = ... - + {-# INLINE f #-} f x = g (g x) If we were to inline g into f's inlining, then an importing module would never be able to do - f e --> g (g e) ---> RULE fires + f e --> g (g e) ---> RULE fires because the InlineRule for f has had g inlined into it. On the other hand, it is bad not to do ANY inlining into an @@ -554,23 +547,23 @@ not to inline wrappers, because doing so inhibits floating ==> ...(case x of I# x# -> case fw x# of ...)... and now the redex (f x) isn't floatable any more. -The no-inlining thing is also important for Template Haskell. You might be +The no-inlining thing is also important for Template Haskell. You might be compiling in one-shot mode with -O2; but when TH compiles a splice before running it, we don't want to use -O2. Indeed, we don't want to inline -anything, because the byte-code interpreter might get confused about +anything, because the byte-code interpreter might get confused about unboxed tuples and suchlike. Note [Simplifying inside InlineRules] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We must take care with simplification inside InlineRules (which come from -INLINE pragmas). +INLINE pragmas). First, consider the following example - let f = \pq -> BIG - in - let g = \y -> f y y - {-# INLINE g #-} - in ...g...g...g...g...g... + let f = \pq -> BIG + in + let g = \y -> f y y + {-# INLINE g #-} + in ...g...g...g...g...g... Now, if that's the ONLY occurrence of f, it might be inlined inside g, and thence copied multiple times when g is inlined. HENCE we treat any occurrence in an InlineRule as a multiple occurrence, not a single @@ -581,12 +574,12 @@ partly to eliminate senseless crap, and partly to break the recursive knots generated by instance declarations. However, suppose we have - {-# INLINE <act> f #-} - f = <rhs> -meaning "inline f in phases p where activation <act>(p) holds". + {-# INLINE <act> f #-} + f = <rhs> +meaning "inline f in phases p where activation <act>(p) holds". Then what inlinings/rules can we apply to the copy of <rhs> captured in f's InlineRule? Our model is that literally <rhs> is substituted for -f when it is inlined. So our conservative plan (implemented by +f when it is inlined. So our conservative plan (implemented by updModeForInlineRules) is this: ------------------------------------------------------------- @@ -596,7 +589,7 @@ updModeForInlineRules) is this: That ensures that - a) Rules/inlinings that *cease* being active before p will + a) Rules/inlinings that *cease* being active before p will not apply to the InlineRule rhs, consistent with it being inlined in its *original* form in phase p. @@ -604,23 +597,23 @@ That ensures that not apply to the InlineRule rhs, again to be consistent with inlining the *original* rhs in phase p. -For example, - {-# INLINE f #-} - f x = ...g... +For example, + {-# INLINE f #-} + f x = ...g... - {-# NOINLINE [1] g #-} - g y = ... + {-# NOINLINE [1] g #-} + g y = ... - {-# RULE h g = ... #-} + {-# RULE h g = ... #-} Here we must not inline g into f's RHS, even when we get to phase 0, because when f is later inlined into some other module we want the rule for h to fire. Similarly, consider - {-# INLINE f #-} - f x = ...g... + {-# INLINE f #-} + f x = ...g... - g y = ... + g y = ... and suppose that there are auto-generated specialisations and a strictness wrapper for g. The specialisations get activation AlwaysActive, and the strictness wrapper get activation (ActiveAfter 0). So the strictness @@ -632,12 +625,12 @@ A note about wrappers ~~~~~~~~~~~~~~~~~~~~~ It's also important not to inline a worker back into a wrapper. A wrapper looks like - wraper = inline_me (\x -> ...worker... ) + wraper = inline_me (\x -> ...worker... ) Normally, the inline_me prevents the worker getting inlined into the wrapper (initially, the worker's only call site!). But, if the wrapper is sure to be called, the strictness analyser will mark it 'demanded', so when the RHS is simplified, it'll get an ArgOf -continuation. +continuation. \begin{code} activeUnfolding :: SimplEnv -> Id -> Bool @@ -651,8 +644,8 @@ activeUnfolding env getUnfoldingInRuleMatch :: SimplEnv -> IdUnfoldingFun -- When matching in RULE, we want to "look through" an unfolding --- (to see a constructor) if *rules* are on, even if *inlinings* --- are not. A notable example is DFuns, which really we want to +-- (to see a constructor) if *rules* are on, even if *inlinings* +-- are not. A notable example is DFuns, which really we want to -- match in rules like (op dfun) in gentle mode. Another example -- is 'otherwise' which we want exprIsConApp_maybe to be able to -- see very early on @@ -671,7 +664,7 @@ active_unfolding_minimal :: Id -> Bool -- the Id has no top-level binding at all -- -- NB: we used to have a second exception, for data con wrappers. --- On the grounds that we use gentle mode for rule LHSs, and +-- On the grounds that we use gentle mode for rule LHSs, and -- they match better when data con wrappers are inlined. -- But that only really applies to the trivial wrappers (like (:)), -- and they are now constructed as Compulsory unfoldings (in MkId) @@ -704,9 +697,9 @@ activeRule env %************************************************************************ -%* * +%* * preInlineUnconditionally -%* * +%* * %************************************************************************ preInlineUnconditionally @@ -721,30 +714,30 @@ This is much better than first simplifying a perhaps-huge RHS and then inlining and re-simplifying it. Indeed, it can be at least quadratically better. Consider - x1 = e1 - x2 = e2[x1] - x3 = e3[x2] - ...etc... - xN = eN[xN-1] + x1 = e1 + x2 = e2[x1] + x3 = e3[x2] + ...etc... + xN = eN[xN-1] We may end up simplifying e1 N times, e2 N-1 times, e3 N-3 times etc. This can happen with cascades of functions too: - f1 = \x1.e1 - f2 = \xs.e2[f1] - f3 = \xs.e3[f3] - ...etc... + f1 = \x1.e1 + f2 = \xs.e2[f1] + f3 = \xs.e3[f3] + ...etc... THE MAIN INVARIANT is this: - ---- preInlineUnconditionally invariant ----- + ---- preInlineUnconditionally invariant ----- IF preInlineUnconditionally chooses to inline x = <rhs> THEN doing the inlining should not change the occurrence - info for the free vars of <rhs> - ---------------------------------------------- + info for the free vars of <rhs> + ---------------------------------------------- For example, it's tempting to look at trivial binding like - x = y + x = y and inline it unconditionally. But suppose x is used many times, but this is the unique occurrence of y. Then inlining x would change y's occurrence info, which breaks the invariant. It matters: y @@ -756,8 +749,8 @@ no benefit from inlining at the call site. [Sept 01] Don't unconditionally inline a top-level thing, because that can simply make a static thing into something built dynamically. E.g. - x = (a,b) - main = \s -> h x + x = (a,b) + main = \s -> h x [Remember that we treat \s as a one-shot lambda.] No point in inlining x unless there is something interesting about the call site. @@ -793,7 +786,7 @@ Example {-# INLINE f #-} f :: Eq a => a -> a f x = ... - + fInt :: Int -> Int fInt = f Int dEqInt @@ -821,47 +814,47 @@ the former. \begin{code} preInlineUnconditionally :: SimplEnv -> TopLevelFlag -> InId -> InExpr -> Bool preInlineUnconditionally env top_lvl bndr rhs - | not active = False - | isStableUnfolding (idUnfolding bndr) = False -- Note [InlineRule and preInlineUnconditionally] - | isTopLevel top_lvl && isBottomingId bndr = False -- Note [Top-level bottoming Ids] + | not active = False + | isStableUnfolding (idUnfolding bndr) = False -- Note [InlineRule and preInlineUnconditionally] + | isTopLevel top_lvl && isBottomingId bndr = False -- Note [Top-level bottoming Ids] | opt_SimplNoPreInlining = False | isCoVar bndr = False -- Note [Do not inline CoVars unconditionally] | otherwise = case idOccInfo bndr of - IAmDead -> True -- Happens in ((\x.1) v) - OneOcc in_lam True int_cxt -> try_once in_lam int_cxt - _ -> False + IAmDead -> True -- Happens in ((\x.1) v) + OneOcc in_lam True int_cxt -> try_once in_lam int_cxt + _ -> False where mode = getMode env active = isActive (sm_phase mode) act -- See Note [pre/postInlineUnconditionally in gentle mode] act = idInlineActivation bndr - try_once in_lam int_cxt -- There's one textual occurrence - | not in_lam = isNotTopLevel top_lvl || early_phase - | otherwise = int_cxt && canInlineInLam rhs + try_once in_lam int_cxt -- There's one textual occurrence + | not in_lam = isNotTopLevel top_lvl || early_phase + | otherwise = int_cxt && canInlineInLam rhs --- Be very careful before inlining inside a lambda, because (a) we must not +-- Be very careful before inlining inside a lambda, because (a) we must not -- invalidate occurrence information, and (b) we want to avoid pushing a --- single allocation (here) into multiple allocations (inside lambda). +-- single allocation (here) into multiple allocations (inside lambda). -- Inlining a *function* with a single *saturated* call would be ok, mind you. --- || (if is_cheap && not (canInlineInLam rhs) then pprTrace "preinline" (ppr bndr <+> ppr rhs) ok else ok) --- where --- is_cheap = exprIsCheap rhs --- ok = is_cheap && int_cxt - - -- int_cxt The context isn't totally boring - -- E.g. let f = \ab.BIG in \y. map f xs - -- Don't want to substitute for f, because then we allocate - -- its closure every time the \y is called +-- || (if is_cheap && not (canInlineInLam rhs) then pprTrace "preinline" (ppr bndr <+> ppr rhs) ok else ok) +-- where +-- is_cheap = exprIsCheap rhs +-- ok = is_cheap && int_cxt + + -- int_cxt The context isn't totally boring + -- E.g. let f = \ab.BIG in \y. map f xs + -- Don't want to substitute for f, because then we allocate + -- its closure every time the \y is called -- But: let f = \ab.BIG in \y. map (f y) xs - -- Now we do want to substitute for f, even though it's not - -- saturated, because we're going to allocate a closure for - -- (f y) every time round the loop anyhow. - - -- canInlineInLam => free vars of rhs are (Once in_lam) or Many, - -- so substituting rhs inside a lambda doesn't change the occ info. - -- Sadly, not quite the same as exprIsHNF. - canInlineInLam (Lit _) = True - canInlineInLam (Lam b e) = isRuntimeVar b || canInlineInLam e + -- Now we do want to substitute for f, even though it's not + -- saturated, because we're going to allocate a closure for + -- (f y) every time round the loop anyhow. + + -- canInlineInLam => free vars of rhs are (Once in_lam) or Many, + -- so substituting rhs inside a lambda doesn't change the occ info. + -- Sadly, not quite the same as exprIsHNF. + canInlineInLam (Lit _) = True + canInlineInLam (Lam b e) = isRuntimeVar b || canInlineInLam e canInlineInLam _ = False -- not ticks. Counting ticks cannot be duplicated, and non-counting -- ticks around a Lam will disappear anyway. @@ -870,26 +863,26 @@ preInlineUnconditionally env top_lvl bndr rhs Phase 0 -> False _ -> True -- If we don't have this early_phase test, consider --- x = length [1,2,3] +-- x = length [1,2,3] -- The full laziness pass carefully floats all the cons cells to -- top level, and preInlineUnconditionally floats them all back in. -- Result is (a) static allocation replaced by dynamic allocation --- (b) many simplifier iterations because this tickles --- a related problem; only one inlining per pass --- +-- (b) many simplifier iterations because this tickles +-- a related problem; only one inlining per pass +-- -- On the other hand, I have seen cases where top-level fusion is -- lost if we don't inline top level thing (e.g. string constants) -- Hence the test for phase zero (which is the phase for all the final -- simplifications). Until phase zero we take no special notice of -- top level things, but then we become more leery about inlining --- them. +-- them. \end{code} %************************************************************************ -%* * +%* * postInlineUnconditionally -%* * +%* * %************************************************************************ postInlineUnconditionally @@ -900,7 +893,7 @@ trivial RHS. If so, we can inline and discard the binding altogether. NB: a loop breaker has must_keep_binding = True and non-loop-breakers only have *forward* references. Hence, it's safe to discard the binding - + NOTE: This isn't our last opportunity to inline. We're at the binding site right now, and we'll get another opportunity when we get to the ocurrence(s) @@ -921,72 +914,72 @@ our new view that inlining is like a RULE, so I'm sticking to the 'active' story for now. \begin{code} -postInlineUnconditionally +postInlineUnconditionally :: DynFlags -> SimplEnv -> TopLevelFlag - -> OutId -- The binder (an InId would be fine too) - -- (*not* a CoVar) - -> OccInfo -- From the InId + -> OutId -- The binder (an InId would be fine too) + -- (*not* a CoVar) + -> OccInfo -- From the InId -> OutExpr -> Unfolding -> Bool postInlineUnconditionally dflags env top_lvl bndr occ_info rhs unfolding - | not active = False - | isWeakLoopBreaker occ_info = False -- If it's a loop-breaker of any kind, don't inline - -- because it might be referred to "earlier" + | not active = False + | isWeakLoopBreaker occ_info = False -- If it's a loop-breaker of any kind, don't inline + -- because it might be referred to "earlier" | isExportedId bndr = False - | isStableUnfolding unfolding = False -- Note [InlineRule and postInlineUnconditionally] - | isTopLevel top_lvl = False -- Note [Top level and postInlineUnconditionally] - | exprIsTrivial rhs = True + | isStableUnfolding unfolding = False -- Note [InlineRule and postInlineUnconditionally] + | isTopLevel top_lvl = False -- Note [Top level and postInlineUnconditionally] + | exprIsTrivial rhs = True | otherwise = case occ_info of - -- The point of examining occ_info here is that for *non-values* - -- that occur outside a lambda, the call-site inliner won't have - -- a chance (becuase it doesn't know that the thing - -- only occurs once). The pre-inliner won't have gotten - -- it either, if the thing occurs in more than one branch - -- So the main target is things like - -- let x = f y in - -- case v of - -- True -> case x of ... - -- False -> case x of ... - -- This is very important in practice; e.g. wheel-seive1 doubles - -- in allocation if you miss this out - OneOcc in_lam _one_br int_cxt -- OneOcc => no code-duplication issue - -> smallEnoughToInline dflags unfolding -- Small enough to dup - -- ToDo: consider discount on smallEnoughToInline if int_cxt is true - -- - -- NB: Do NOT inline arbitrarily big things, even if one_br is True - -- Reason: doing so risks exponential behaviour. We simplify a big - -- expression, inline it, and simplify it again. But if the - -- very same thing happens in the big expression, we get - -- exponential cost! - -- PRINCIPLE: when we've already simplified an expression once, - -- make sure that we only inline it if it's reasonably small. - - && (not in_lam || - -- Outside a lambda, we want to be reasonably aggressive - -- about inlining into multiple branches of case - -- e.g. let x = <non-value> - -- in case y of { C1 -> ..x..; C2 -> ..x..; C3 -> ... } - -- Inlining can be a big win if C3 is the hot-spot, even if - -- the uses in C1, C2 are not 'interesting' - -- An example that gets worse if you add int_cxt here is 'clausify' - - (isCheapUnfolding unfolding && int_cxt)) - -- isCheap => acceptable work duplication; in_lam may be true - -- int_cxt to prevent us inlining inside a lambda without some - -- good reason. See the notes on int_cxt in preInlineUnconditionally - - IAmDead -> True -- 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 ... + -- The point of examining occ_info here is that for *non-values* + -- that occur outside a lambda, the call-site inliner won't have + -- a chance (becuase it doesn't know that the thing + -- only occurs once). The pre-inliner won't have gotten + -- it either, if the thing occurs in more than one branch + -- So the main target is things like + -- let x = f y in + -- case v of + -- True -> case x of ... + -- False -> case x of ... + -- This is very important in practice; e.g. wheel-seive1 doubles + -- in allocation if you miss this out + OneOcc in_lam _one_br int_cxt -- OneOcc => no code-duplication issue + -> smallEnoughToInline dflags unfolding -- Small enough to dup + -- ToDo: consider discount on smallEnoughToInline if int_cxt is true + -- + -- NB: Do NOT inline arbitrarily big things, even if one_br is True + -- Reason: doing so risks exponential behaviour. We simplify a big + -- expression, inline it, and simplify it again. But if the + -- very same thing happens in the big expression, we get + -- exponential cost! + -- PRINCIPLE: when we've already simplified an expression once, + -- make sure that we only inline it if it's reasonably small. + + && (not in_lam || + -- Outside a lambda, we want to be reasonably aggressive + -- about inlining into multiple branches of case + -- e.g. let x = <non-value> + -- in case y of { C1 -> ..x..; C2 -> ..x..; C3 -> ... } + -- Inlining can be a big win if C3 is the hot-spot, even if + -- the uses in C1, C2 are not 'interesting' + -- An example that gets worse if you add int_cxt here is 'clausify' + + (isCheapUnfolding unfolding && int_cxt)) + -- isCheap => acceptable work duplication; in_lam may be true + -- int_cxt to prevent us inlining inside a lambda without some + -- good reason. See the notes on int_cxt in preInlineUnconditionally + + IAmDead -> True -- 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 ... _ -> False -- Here's an example that we don't handle well: --- let f = if b then Left (\x.BIG) else Right (\y.BIG) --- in \y. ....case f of {...} .... +-- let f = if b then Left (\x.BIG) else Right (\y.BIG) +-- in \y. ....case f of {...} .... -- Here f is used just once, and duplicating the case work is fine (exprIsCheap). -- But -- - We can't preInlineUnconditionally because that woud invalidate @@ -1007,14 +1000,14 @@ We don't do postInlineUnconditionally for top-level things (even for ones that are trivial): * Doing so will inline top-level error expressions that have been - carefully floated out by FloatOut. More generally, it might + carefully floated out by FloatOut. More generally, it might replace static allocation with dynamic. * Even for trivial expressions there's a problem. Consider {-# RULE "foo" forall (xs::[T]). reverse xs = ruggle xs #-} blah xs = reverse xs ruggle = sort - In one simplifier pass we might fire the rule, getting + In one simplifier pass we might fire the rule, getting blah xs = ruggle xs but in *that* simplifier pass we must not do postInlineUnconditionally on 'ruggle' because then we'll have an unbound occurrence of 'ruggle' @@ -1023,8 +1016,8 @@ ones that are trivial): the binding will be dead and discarded by the next use of OccurAnal * There is less point, because the main goal is to get rid of local - bindings used in multiple case branches. - + bindings used in multiple case branches. + * The inliner should inline trivial things at call sites anyway. Note [InlineRule and postInlineUnconditionally] @@ -1048,32 +1041,32 @@ won't inline because 'e' is too big. %************************************************************************ -%* * - Rebuilding a lambda -%* * +%* * + Rebuilding a lambda +%* * %************************************************************************ \begin{code} mkLam :: SimplEnv -> [OutBndr] -> OutExpr -> SimplM OutExpr -- mkLam tries three things --- a) eta reduction, if that gives a trivial expression --- b) eta expansion [only if there are some value lambdas] +-- a) eta reduction, if that gives a trivial expression +-- b) eta expansion [only if there are some value lambdas] -mkLam _b [] body +mkLam _b [] body = return body mkLam _env bndrs body - = do { dflags <- getDynFlags - ; mkLam' dflags bndrs body } + = do { dflags <- getDynFlags + ; mkLam' dflags bndrs body } where mkLam' :: DynFlags -> [OutBndr] -> OutExpr -> SimplM OutExpr mkLam' dflags bndrs (Cast body co) | not (any bad bndrs) - -- Note [Casts and lambdas] + -- Note [Casts and lambdas] = do { lam <- mkLam' dflags bndrs body ; return (mkCast lam (mkPiCos bndrs co)) } where co_vars = tyCoVarsOfCo co - bad bndr = isCoVar bndr && bndr `elemVarSet` co_vars + bad bndr = isCoVar bndr && bndr `elemVarSet` co_vars mkLam' dflags bndrs body@(Lam {}) = mkLam' dflags (bndrs ++ bndrs1) body1 @@ -1084,7 +1077,7 @@ mkLam _env bndrs body | dopt Opt_DoEtaReduction dflags , Just etad_lam <- tryEtaReduce bndrs body = do { tick (EtaReduction (head bndrs)) - ; return etad_lam } + ; return etad_lam } | otherwise = return (mkLams bndrs body) @@ -1093,40 +1086,40 @@ mkLam _env bndrs body Note [Casts and lambdas] ~~~~~~~~~~~~~~~~~~~~~~~~ -Consider - (\x. (\y. e) `cast` g1) `cast` g2 -There is a danger here that the two lambdas look separated, and the +Consider + (\x. (\y. e) `cast` g1) `cast` g2 +There is a danger here that the two lambdas look separated, and the full laziness pass might float an expression to between the two. So this equation in mkLam' floats the g1 out, thus: - (\x. e `cast` g1) --> (\x.e) `cast` (tx -> g1) + (\x. e `cast` g1) --> (\x.e) `cast` (tx -> g1) where x:tx. In general, this floats casts outside lambdas, where (I hope) they might meet and cancel with some other cast: - \x. e `cast` co ===> (\x. e) `cast` (tx -> co) - /\a. e `cast` co ===> (/\a. e) `cast` (/\a. co) - /\g. e `cast` co ===> (/\g. e) `cast` (/\g. co) - (if not (g `in` co)) + \x. e `cast` co ===> (\x. e) `cast` (tx -> co) + /\a. e `cast` co ===> (/\a. e) `cast` (/\a. co) + /\g. e `cast` co ===> (/\g. e) `cast` (/\g. co) + (if not (g `in` co)) Notice that it works regardless of 'e'. Originally it worked only -if 'e' was itself a lambda, but in some cases that resulted in +if 'e' was itself a lambda, but in some cases that resulted in fruitless iteration in the simplifier. A good example was when -compiling Text.ParserCombinators.ReadPrec, where we had a definition -like (\x. Get `cast` g) +compiling Text.ParserCombinators.ReadPrec, where we had a definition +like (\x. Get `cast` g) where Get is a constructor with nonzero arity. Then mkLam eta-expanded -the Get, and the next iteration eta-reduced it, and then eta-expanded +the Get, and the next iteration eta-reduced it, and then eta-expanded it again. Note also the side condition for the case of coercion binders. It does not make sense to transform - /\g. e `cast` g ==> (/\g.e) `cast` (/\g.g) + /\g. e `cast` g ==> (/\g.e) `cast` (/\g.g) because the latter is not well-kinded. %************************************************************************ -%* * - Eta expansion -%* * +%* * + Eta expansion +%* * %************************************************************************ \begin{code} @@ -1136,10 +1129,10 @@ tryEtaExpand env bndr rhs = do { dflags <- getDynFlags ; (new_arity, new_rhs) <- try_expand dflags - ; WARN( new_arity < old_arity || new_arity < _dmd_arity, + ; WARN( new_arity < old_arity || new_arity < _dmd_arity, (ptext (sLit "Arity decrease:") <+> (ppr bndr <+> ppr old_arity - <+> ppr new_arity <+> ppr _dmd_arity) $$ ppr new_rhs) ) - -- Note [Arity decrease] + <+> ppr new_arity <+> ppr _dmd_arity) $$ ppr new_rhs) ) + -- Note [Arity decrease] return (new_arity, new_rhs) } where try_expand dflags @@ -1148,8 +1141,8 @@ tryEtaExpand env bndr rhs | sm_eta_expand (getMode env) -- Provided eta-expansion is on , let new_arity = findArity dflags bndr rhs old_arity - , new_arity > manifest_arity -- And the curent manifest arity isn't enough - -- See Note [Eta expansion to manifes arity] + , new_arity > manifest_arity -- And the curent manifest arity isn't enough + -- See Note [Eta expansion to manifes arity] = do { tick (EtaExpansion bndr) ; return (new_arity, etaExpand new_arity rhs) } | otherwise @@ -1164,7 +1157,7 @@ findArity :: DynFlags -> Id -> CoreExpr -> Arity -> Arity -- See Note [Arity analysis] findArity dflags bndr rhs old_arity = go (exprEtaExpandArity dflags init_cheap_app rhs) - -- We always call exprEtaExpandArity once, but usually + -- We always call exprEtaExpandArity once, but usually -- that produces a result equal to old_arity, and then -- we stop right away (since arities should not decrease) -- Result: the common case is that there is just one iteration @@ -1176,11 +1169,11 @@ findArity dflags bndr rhs old_arity go :: Arity -> Arity go cur_arity - | cur_arity <= old_arity = cur_arity + | cur_arity <= old_arity = cur_arity | new_arity == cur_arity = cur_arity | otherwise = ASSERT( new_arity < cur_arity ) #ifdef DEBUG - pprTrace "Exciting arity" + pprTrace "Exciting arity" (vcat [ ppr bndr <+> ppr cur_arity <+> ppr new_arity , ppr rhs]) #endif @@ -1196,8 +1189,8 @@ findArity dflags bndr rhs old_arity Note [Eta-expanding at let bindings] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -We now eta expand at let-bindings, which is where the payoff -comes. +We now eta expand at let-bindings, which is where the payoff +comes. One useful consequence is this example: genMap :: C a => ... @@ -1209,10 +1202,10 @@ One useful consequence is this example: myMap = genMap Notice that 'genMap' should only inline if applied to two arguments. -In the InlineRule for myMap we'll have the unfolding - (\d -> genMap Int (..d..)) -We do not want to eta-expand to - (\d f xs -> genMap Int (..d..) f xs) +In the InlineRule for myMap we'll have the unfolding + (\d -> genMap Int (..d..)) +We do not want to eta-expand to + (\d f xs -> genMap Int (..d..) f xs) because then 'genMap' will inline, and it really shouldn't: at least as far as the programmer is concerned, it's not applied to two arguments! @@ -1226,9 +1219,9 @@ we *eta-contract* if that yields a trivial RHS.) Otherwise we eta-expand to produce enough manifest lambdas. This *does* eta-expand partial applications. eg - x = map g --> x = \v -> map g v - y = \_ -> map g --> y = \_ v -> map g v -One benefit this is that in the definition of y there was + x = map g --> x = \v -> map g v + y = \_ -> map g --> y = \_ v -> map g v +One benefit this is that in the definition of y there was a danger that full laziness would transform to lvl = map g y = \_ -> lvl @@ -1237,8 +1230,8 @@ which is stupid. This doesn't happen in the eta-expanded form. Note [Arity analysis] ~~~~~~~~~~~~~~~~~~~~~ The motivating example for arity analysis is this: - - f = \x. let g = f (x+1) + + f = \x. let g = f (x+1) in \y. ...g... What arity does f have? Really it should have arity 2, but a naive @@ -1252,7 +1245,7 @@ in Trac #4138. The analysis is easy to achieve because exprEtaExpandArity takes an argument type CheapFun = CoreExpr -> Maybe Type -> Bool -used to decide if an expression is cheap enough to push inside a +used to decide if an expression is cheap enough to push inside a lambda. And exprIsCheap' in turn takes an argument type CheapAppFun = Id -> Int -> Bool which tells when an application is cheap. This makes it easy to @@ -1263,54 +1256,54 @@ mutual recursion. But the self-recursive case is the important one. %************************************************************************ -%* * +%* * \subsection{Floating lets out of big lambdas} -%* * +%* * %************************************************************************ Note [Floating and type abstraction] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider this: - x = /\a. C e1 e2 -We'd like to float this to - y1 = /\a. e1 - y2 = /\a. e2 - x = /\a. C (y1 a) (y2 a) + x = /\a. C e1 e2 +We'd like to float this to + y1 = /\a. e1 + y2 = /\a. e2 + x = /\a. C (y1 a) (y2 a) for the usual reasons: we want to inline x rather vigorously. You may think that this kind of thing is rare. But in some programs it is common. For example, if you do closure conversion you might get: - data a :-> b = forall e. (e -> a -> b) :$ e + data a :-> b = forall e. (e -> a -> b) :$ e - f_cc :: forall a. a :-> a - f_cc = /\a. (\e. id a) :$ () + f_cc :: forall a. a :-> a + f_cc = /\a. (\e. id a) :$ () Now we really want to inline that f_cc thing so that the -construction of the closure goes away. +construction of the closure goes away. So I have elaborated simplLazyBind to understand right-hand sides that look like - /\ a1..an. body + /\ a1..an. body and treat them specially. The real work is done in SimplUtils.abstractFloats, but there is quite a bit of plumbing in simplLazyBind as well. The same transformation is good when there are lets in the body: - /\abc -> let(rec) x = e in b + /\abc -> let(rec) x = e in b ==> - let(rec) x' = /\abc -> let x = x' a b c in e - in - /\abc -> let x = x' a b c in b + let(rec) x' = /\abc -> let x = x' a b c in e + in + /\abc -> let x = x' a b c in b This is good because it can turn things like: - let f = /\a -> letrec g = ... g ... in g + let f = /\a -> letrec g = ... g ... in g into - letrec g' = /\a -> ... g' a ... - in - let f = /\ a -> g' a + letrec g' = /\a -> ... g' a ... + in + let f = /\ a -> g' a which is better. In effect, it means that big lambdas don't impede let-floating. @@ -1319,22 +1312,22 @@ This optimisation is CRUCIAL in eliminating the junk introduced by desugaring mutually recursive definitions. Don't eliminate it lightly! [May 1999] If we do this transformation *regardless* then we can -end up with some pretty silly stuff. For example, +end up with some pretty silly stuff. For example, - let - st = /\ s -> let { x1=r1 ; x2=r2 } in ... - in .. + let + st = /\ s -> let { x1=r1 ; x2=r2 } in ... + in .. becomes - let y1 = /\s -> r1 - y2 = /\s -> r2 - st = /\s -> ...[y1 s/x1, y2 s/x2] - in .. + let y1 = /\s -> r1 + y2 = /\s -> r2 + st = /\s -> ...[y1 s/x1, y2 s/x2] + in .. Unless the "..." is a WHNF there is really no point in doing this. Indeed it can make things worse. Suppose x1 is used strictly, and is of the form - x1* = case f y of { (a,b) -> e } + x1* = case f y of { (a,b) -> e } If we abstract this wrt the tyvar we then can't do the case inline as we would normally do. @@ -1348,8 +1341,8 @@ it is guarded by the doFloatFromRhs call in simplLazyBind. abstractFloats :: [OutTyVar] -> SimplEnv -> OutExpr -> SimplM ([OutBind], OutExpr) abstractFloats main_tvs body_env body = ASSERT( notNull body_floats ) - do { (subst, float_binds) <- mapAccumLM abstract empty_subst body_floats - ; return (float_binds, CoreSubst.substExpr (text "abstract_floats1") subst body) } + do { (subst, float_binds) <- mapAccumLM abstract empty_subst body_floats + ; return (float_binds, CoreSubst.substExpr (text "abstract_floats1") subst body) } where main_tv_set = mkVarSet main_tvs body_floats = getFloatBinds body_env @@ -1358,71 +1351,71 @@ abstractFloats main_tvs body_env body abstract :: CoreSubst.Subst -> OutBind -> SimplM (CoreSubst.Subst, OutBind) abstract subst (NonRec id rhs) = do { (poly_id, poly_app) <- mk_poly tvs_here id - ; let poly_rhs = mkLams tvs_here rhs' - subst' = CoreSubst.extendIdSubst subst id poly_app - ; return (subst', (NonRec poly_id poly_rhs)) } + ; let poly_rhs = mkLams tvs_here rhs' + subst' = CoreSubst.extendIdSubst subst id poly_app + ; return (subst', (NonRec poly_id poly_rhs)) } where - rhs' = CoreSubst.substExpr (text "abstract_floats2") subst rhs - tvs_here = varSetElemsKvsFirst (main_tv_set `intersectVarSet` exprSomeFreeVars isTyVar rhs') - - -- Abstract only over the type variables free in the rhs - -- wrt which the new binding is abstracted. But the naive - -- approach of abstract wrt the tyvars free in the Id's type - -- fails. Consider: - -- /\ a b -> let t :: (a,b) = (e1, e2) - -- x :: a = fst t - -- in ... - -- Here, b isn't free in x's type, but we must nevertheless - -- abstract wrt b as well, because t's type mentions b. - -- Since t is floated too, we'd end up with the bogus: - -- poly_t = /\ a b -> (e1, e2) - -- poly_x = /\ a -> fst (poly_t a *b*) - -- So for now we adopt the even more naive approach of - -- abstracting wrt *all* the tyvars. We'll see if that - -- gives rise to problems. SLPJ June 98 + rhs' = CoreSubst.substExpr (text "abstract_floats2") subst rhs + tvs_here = varSetElemsKvsFirst (main_tv_set `intersectVarSet` exprSomeFreeVars isTyVar rhs') + + -- Abstract only over the type variables free in the rhs + -- wrt which the new binding is abstracted. But the naive + -- approach of abstract wrt the tyvars free in the Id's type + -- fails. Consider: + -- /\ a b -> let t :: (a,b) = (e1, e2) + -- x :: a = fst t + -- in ... + -- Here, b isn't free in x's type, but we must nevertheless + -- abstract wrt b as well, because t's type mentions b. + -- Since t is floated too, we'd end up with the bogus: + -- poly_t = /\ a b -> (e1, e2) + -- poly_x = /\ a -> fst (poly_t a *b*) + -- So for now we adopt the even more naive approach of + -- abstracting wrt *all* the tyvars. We'll see if that + -- gives rise to problems. SLPJ June 98 abstract subst (Rec prs) = do { (poly_ids, poly_apps) <- mapAndUnzipM (mk_poly tvs_here) ids - ; let subst' = CoreSubst.extendSubstList subst (ids `zip` poly_apps) - poly_rhss = [mkLams tvs_here (CoreSubst.substExpr (text "abstract_floats3") subst' rhs) + ; let subst' = CoreSubst.extendSubstList subst (ids `zip` poly_apps) + poly_rhss = [mkLams tvs_here (CoreSubst.substExpr (text "abstract_floats3") subst' rhs) | rhs <- rhss] - ; return (subst', Rec (poly_ids `zip` poly_rhss)) } + ; return (subst', Rec (poly_ids `zip` poly_rhss)) } where - (ids,rhss) = unzip prs - -- For a recursive group, it's a bit of a pain to work out the minimal - -- set of tyvars over which to abstract: - -- /\ a b c. let x = ...a... in - -- letrec { p = ...x...q... - -- q = .....p...b... } in - -- ... - -- Since 'x' is abstracted over 'a', the {p,q} group must be abstracted - -- over 'a' (because x is replaced by (poly_x a)) as well as 'b'. - -- Since it's a pain, we just use the whole set, which is always safe - -- - -- If you ever want to be more selective, remember this bizarre case too: - -- x::a = x - -- Here, we must abstract 'x' over 'a'. - tvs_here = sortQuantVars main_tvs + (ids,rhss) = unzip prs + -- For a recursive group, it's a bit of a pain to work out the minimal + -- set of tyvars over which to abstract: + -- /\ a b c. let x = ...a... in + -- letrec { p = ...x...q... + -- q = .....p...b... } in + -- ... + -- Since 'x' is abstracted over 'a', the {p,q} group must be abstracted + -- over 'a' (because x is replaced by (poly_x a)) as well as 'b'. + -- Since it's a pain, we just use the whole set, which is always safe + -- + -- If you ever want to be more selective, remember this bizarre case too: + -- x::a = x + -- Here, we must abstract 'x' over 'a'. + tvs_here = sortQuantVars main_tvs mk_poly tvs_here var = do { uniq <- getUniqueM - ; let poly_name = setNameUnique (idName var) uniq -- Keep same name - poly_ty = mkForAllTys tvs_here (idType var) -- But new type of course - poly_id = transferPolyIdInfo var tvs_here $ -- Note [transferPolyIdInfo] in Id.lhs - mkLocalId poly_name poly_ty - ; return (poly_id, mkTyApps (Var poly_id) (mkTyVarTys tvs_here)) } - -- In the olden days, it was crucial to copy the occInfo of the original var, - -- because we were looking at occurrence-analysed but as yet unsimplified code! - -- In particular, we mustn't lose the loop breakers. BUT NOW we are looking - -- at already simplified code, so it doesn't matter - -- - -- It's even right to retain single-occurrence or dead-var info: - -- Suppose we started with /\a -> let x = E in B - -- where x occurs once in B. Then we transform to: - -- let x' = /\a -> E in /\a -> let x* = x' a in B - -- where x* has an INLINE prag on it. Now, once x* is inlined, - -- the occurrences of x' will be just the occurrences originally - -- pinned on x. + ; let poly_name = setNameUnique (idName var) uniq -- Keep same name + poly_ty = mkForAllTys tvs_here (idType var) -- But new type of course + poly_id = transferPolyIdInfo var tvs_here $ -- Note [transferPolyIdInfo] in Id.lhs + mkLocalId poly_name poly_ty + ; return (poly_id, mkTyApps (Var poly_id) (mkTyVarTys tvs_here)) } + -- In the olden days, it was crucial to copy the occInfo of the original var, + -- because we were looking at occurrence-analysed but as yet unsimplified code! + -- In particular, we mustn't lose the loop breakers. BUT NOW we are looking + -- at already simplified code, so it doesn't matter + -- + -- It's even right to retain single-occurrence or dead-var info: + -- Suppose we started with /\a -> let x = E in B + -- where x occurs once in B. Then we transform to: + -- let x' = /\a -> E in /\a -> let x* = x' a in B + -- where x* has an INLINE prag on it. Now, once x* is inlined, + -- the occurrences of x' will be just the occurrences originally + -- pinned on x. \end{code} Note [Abstract over coercions] @@ -1434,30 +1427,30 @@ wrt all the type variables if any of them are coercion variables. Historical note: if you use let-bindings instead of a substitution, beware of this: - -- Suppose we start with: - -- - -- x = /\ a -> let g = G in E - -- - -- Then we'll float to get - -- - -- x = let poly_g = /\ a -> G - -- in /\ a -> let g = poly_g a in E - -- - -- But now the occurrence analyser will see just one occurrence - -- of poly_g, not inside a lambda, so the simplifier will - -- PreInlineUnconditionally poly_g back into g! Badk to square 1! - -- (I used to think that the "don't inline lone occurrences" stuff - -- would stop this happening, but since it's the *only* occurrence, - -- PreInlineUnconditionally kicks in first!) - -- - -- Solution: put an INLINE note on g's RHS, so that poly_g seems - -- to appear many times. (NB: mkInlineMe eliminates - -- such notes on trivial RHSs, so do it manually.) + -- Suppose we start with: + -- + -- x = /\ a -> let g = G in E + -- + -- Then we'll float to get + -- + -- x = let poly_g = /\ a -> G + -- in /\ a -> let g = poly_g a in E + -- + -- But now the occurrence analyser will see just one occurrence + -- of poly_g, not inside a lambda, so the simplifier will + -- PreInlineUnconditionally poly_g back into g! Badk to square 1! + -- (I used to think that the "don't inline lone occurrences" stuff + -- would stop this happening, but since it's the *only* occurrence, + -- PreInlineUnconditionally kicks in first!) + -- + -- Solution: put an INLINE note on g's RHS, so that poly_g seems + -- to appear many times. (NB: mkInlineMe eliminates + -- such notes on trivial RHSs, so do it manually.) %************************************************************************ -%* * - prepareAlts -%* * +%* * + prepareAlts +%* * %************************************************************************ prepareAlts tries these things: @@ -1515,16 +1508,16 @@ prepareAlts scrut case_bndr' alts = do return (imposs_deflt_cons, alts') where imposs_cons = case scrut of - Var v -> otherCons (idUnfolding v) - _ -> [] + Var v -> otherCons (idUnfolding v) + _ -> [] \end{code} %************************************************************************ -%* * - mkCase -%* * +%* * + mkCase +%* * %************************************************************************ mkCase tries these things @@ -1532,16 +1525,16 @@ mkCase tries these things 1. Merge Nested Cases case e of b { ==> case e of b { - p1 -> rhs1 p1 -> rhs1 - ... ... - pm -> rhsm pm -> rhsm - _ -> case b of b' { pn -> let b'=b in rhsn - pn -> rhsn ... - ... po -> let b'=b in rhso - po -> rhso _ -> let b'=b in rhsd - _ -> rhsd - } - + p1 -> rhs1 p1 -> rhs1 + ... ... + pm -> rhsm pm -> rhsm + _ -> case b of b' { pn -> let b'=b in rhsn + pn -> rhsn ... + ... po -> let b'=b in rhso + po -> rhso _ -> let b'=b in rhsd + _ -> rhsd + } + which merges two cases in one case when -- the default alternative of the outer case scrutises the same variable as the outer case. This transformation is called Case Merging. It avoids that the same @@ -1549,99 +1542,99 @@ mkCase tries these things 2. Eliminate Identity Case - case e of ===> e - True -> True; - False -> False + case e of ===> e + True -> True; + False -> False and similar friends. 3. Merge identical alternatives. If several alternatives are identical, merge them into - a single DEFAULT alternative. I've occasionally seen this + a single DEFAULT alternative. I've occasionally seen this making a big difference: - case e of =====> case e of - C _ -> f x D v -> ....v.... - D v -> ....v.... DEFAULT -> f x - DEFAULT -> f x + case e of =====> case e of + C _ -> f x D v -> ....v.... + D v -> ....v.... DEFAULT -> f x + DEFAULT -> f x The point is that we merge common RHSs, at least for the DEFAULT case. [One could do something more elaborate but I've never seen it needed.] To avoid an expensive test, we just merge branches equal to the *first* alternative; this picks up the common cases - a) all branches equal - b) some branches equal to the DEFAULT (which occurs first) + a) all branches equal + b) some branches equal to the DEFAULT (which occurs first) The case where Merge Identical Alternatives transformation showed up was like this (base/Foreign/C/Err/Error.lhs): - x | p `is` 1 -> e1 - | p `is` 2 -> e2 - ...etc... + x | p `is` 1 -> e1 + | p `is` 2 -> e2 + ...etc... where @is@ was something like - - p `is` n = p /= (-1) && p == n + + p `is` n = p /= (-1) && p == n This gave rise to a horrible sequence of cases - case p of - (-1) -> $j p - 1 -> e1 - DEFAULT -> $j p + case p of + (-1) -> $j p + 1 -> e1 + DEFAULT -> $j p and similarly in cascade for all the join points! \begin{code} -mkCase, mkCase1, mkCase2 - :: DynFlags +mkCase, mkCase1, mkCase2 + :: DynFlags -> OutExpr -> OutId - -> OutType -> [OutAlt] -- Alternatives in standard (increasing) order + -> OutType -> [OutAlt] -- Alternatives in standard (increasing) order -> SimplM OutExpr -------------------------------------------------- --- 1. Merge Nested Cases +-- 1. Merge Nested Cases -------------------------------------------------- mkCase dflags scrut outer_bndr alts_ty ((DEFAULT, _, deflt_rhs) : outer_alts) | dopt Opt_CaseMerge dflags , Case (Var inner_scrut_var) inner_bndr _ inner_alts <- deflt_rhs , inner_scrut_var == outer_bndr - = do { tick (CaseMerge outer_bndr) + = do { tick (CaseMerge outer_bndr) - ; let wrap_alt (con, args, rhs) = ASSERT( outer_bndr `notElem` args ) + ; let wrap_alt (con, args, rhs) = ASSERT( outer_bndr `notElem` args ) (con, args, wrap_rhs rhs) - -- Simplifier's no-shadowing invariant should ensure - -- that outer_bndr is not shadowed by the inner patterns + -- Simplifier's no-shadowing invariant should ensure + -- that outer_bndr is not shadowed by the inner patterns wrap_rhs rhs = Let (NonRec inner_bndr (Var outer_bndr)) rhs - -- The let is OK even for unboxed binders, + -- The let is OK even for unboxed binders, - wrapped_alts | isDeadBinder inner_bndr = inner_alts + wrapped_alts | isDeadBinder inner_bndr = inner_alts | otherwise = map wrap_alt inner_alts - merged_alts = mergeAlts outer_alts wrapped_alts - -- NB: mergeAlts gives priority to the left - -- case x of - -- A -> e1 - -- DEFAULT -> case x of - -- A -> e2 - -- B -> e3 - -- When we merge, we must ensure that e1 takes - -- precedence over e2 as the value for A! - - ; mkCase1 dflags scrut outer_bndr alts_ty merged_alts - } - -- Warning: don't call mkCase recursively! - -- Firstly, there's no point, because inner alts have already had - -- mkCase applied to them, so they won't have a case in their default - -- Secondly, if you do, you get an infinite loop, because the bindCaseBndr - -- in munge_rhs may put a case into the DEFAULT branch! + merged_alts = mergeAlts outer_alts wrapped_alts + -- NB: mergeAlts gives priority to the left + -- case x of + -- A -> e1 + -- DEFAULT -> case x of + -- A -> e2 + -- B -> e3 + -- When we merge, we must ensure that e1 takes + -- precedence over e2 as the value for A! + + ; mkCase1 dflags scrut outer_bndr alts_ty merged_alts + } + -- Warning: don't call mkCase recursively! + -- Firstly, there's no point, because inner alts have already had + -- mkCase applied to them, so they won't have a case in their default + -- Secondly, if you do, you get an infinite loop, because the bindCaseBndr + -- in munge_rhs may put a case into the DEFAULT branch! mkCase dflags scrut bndr alts_ty alts = mkCase1 dflags scrut bndr alts_ty alts -------------------------------------------------- --- 2. Eliminate Identity Case +-- 2. Eliminate Identity Case -------------------------------------------------- mkCase1 _dflags scrut case_bndr _ alts@((_,_,rhs1) : _) -- Identity case @@ -1663,39 +1656,39 @@ mkCase1 _dflags scrut case_bndr _ alts@((_,_,rhs1) : _) -- Identity case -- Note [RHS casts] -- ~~~~~~~~~~~~~~~~ - -- We've seen this: - -- case e of x { _ -> x `cast` c } - -- And we definitely want to eliminate this case, to give - -- e `cast` c - -- So we throw away the cast from the RHS, and reconstruct - -- it at the other end. All the RHS casts must be the same - -- if (all identity_alt alts) holds. - -- - -- Don't worry about nested casts, because the simplifier combines them + -- We've seen this: + -- case e of x { _ -> x `cast` c } + -- And we definitely want to eliminate this case, to give + -- e `cast` c + -- So we throw away the cast from the RHS, and reconstruct + -- it at the other end. All the RHS casts must be the same + -- if (all identity_alt alts) holds. + -- + -- Don't worry about nested casts, because the simplifier combines them re_cast scrut (Cast rhs co) = Cast (re_cast scrut rhs) co re_cast scrut _ = scrut -------------------------------------------------- --- 3. Merge Identical Alternatives +-- 3. Merge Identical Alternatives -------------------------------------------------- mkCase1 dflags scrut case_bndr alts_ty ((_con1,bndrs1,rhs1) : con_alts) - | all isDeadBinder bndrs1 -- Remember the default - , length filtered_alts < length con_alts -- alternative comes first - -- Also Note [Dead binders] - = do { tick (AltMerge case_bndr) - ; mkCase2 dflags scrut case_bndr alts_ty alts' } + | all isDeadBinder bndrs1 -- Remember the default + , length filtered_alts < length con_alts -- alternative comes first + -- Also Note [Dead binders] + = do { tick (AltMerge case_bndr) + ; mkCase2 dflags scrut case_bndr alts_ty alts' } where alts' = (DEFAULT, [], rhs1) : filtered_alts - filtered_alts = filter keep con_alts + filtered_alts = filter keep con_alts keep (_con,bndrs,rhs) = not (all isDeadBinder bndrs && rhs `cheapEqExpr` rhs1) mkCase1 dflags scrut bndr alts_ty alts = mkCase2 dflags scrut bndr alts_ty alts -------------------------------------------------- --- Catch-all +-- Catch-all -------------------------------------------------- -mkCase2 _dflags scrut bndr alts_ty alts +mkCase2 _dflags scrut bndr alts_ty alts = return (Case scrut bndr alts_ty alts) \end{code} @@ -1711,7 +1704,7 @@ Case merging should cascade in one sweep, because it happens bottom-up case e of a { - DEFAULT -> case a of b + DEFAULT -> case a of b DEFAULT -> case b of c { DEFAULT -> e A -> ea @@ -1719,7 +1712,7 @@ happens bottom-up C -> ec ==> case e of a { - DEFAULT -> case a of b + DEFAULT -> case a of b DEFAULT -> let c = b in e A -> let c = b in ea B -> eb @@ -1742,10 +1735,10 @@ see how to catch it in one pass: case a2 of ... After occurrence analysis (and its binder-swap) we get this - - case x of c1 { I# a1 -> - let x = c1 in -- Binder-swap addition - case a1 of c2 -> + + case x of c1 { I# a1 -> + let x = c1 in -- Binder-swap addition + case a1 of c2 -> 0 -> ... DEFAULT -> case x of c3 { I# a2 -> case a2 of ... @@ -1753,16 +1746,16 @@ After occurrence analysis (and its binder-swap) we get this When we simplify the inner case x, we'll see that x=c1=I# a1. So we'll bind a2 to a1, and get - case x of c1 { I# a1 -> - case a1 of c2 -> + case x of c1 { I# a1 -> + case a1 of c2 -> 0 -> ... DEFAULT -> case a1 of ... This is corect, but we can't do a case merge in this sweep because c2 /= a1. Reason: the binding c1=I# a1 went inwards -without getting changed to c1=I# c2. +without getting changed to c1=I# c2. I don't think this is worth fixing, even if I knew how. It'll all come out in the next pass anyway. - + |