X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FsimplCore%2FOccurAnal.lhs;h=7692b628abef16a25f7a4131a5b87dbdb039ee79;hb=6f66d02c9654fc037db0582857acdcc15e0fd1d3;hp=ba8b5cbbe3ace26ee5ebb7ddcb210e31a3ed3789;hpb=5e218036aabd1666ff2b509436e4e88491596c37;p=ghc-hetmet.git diff --git a/compiler/simplCore/OccurAnal.lhs b/compiler/simplCore/OccurAnal.lhs index ba8b5cb..7692b62 100644 --- a/compiler/simplCore/OccurAnal.lhs +++ b/compiler/simplCore/OccurAnal.lhs @@ -107,7 +107,7 @@ occAnalBind env _ (NonRec binder rhs) body_usage = (body_usage' +++ rhs_usage3, [NonRec tagged_binder rhs']) where (body_usage', tagged_binder) = tagBinder body_usage binder - (rhs_usage1, rhs') = occAnalRhs env (idOccInfo tagged_binder) rhs + (rhs_usage1, rhs') = occAnalRhs env (Just tagged_binder) rhs rhs_usage2 = addIdOccs rhs_usage1 (idUnfoldingVars binder) rhs_usage3 = addIdOccs rhs_usage2 (idRuleVars binder) -- See Note [Rules are extra RHSs] and Note [Rule dependency info] @@ -385,7 +385,7 @@ occAnalBind _ env (Rec pairs) body_usage details = ND { nd_bndr = bndr, nd_rhs = rhs' , nd_uds = rhs_usage3, nd_inl = inl_fvs} - (rhs_usage1, rhs') = occAnalRhs env NoOccInfo rhs + (rhs_usage1, rhs') = occAnalRhs env Nothing rhs rhs_usage2 = addIdOccs rhs_usage1 rule_fvs -- Note [Rules are extra RHSs] rhs_usage3 = addIdOccs rhs_usage2 unf_fvs unf = realIdUnfolding bndr -- Ignore any current loop-breaker flag @@ -790,36 +790,27 @@ ToDo: try using the occurrence info for the inline'd binder. \begin{code} occAnalRhs :: OccEnv - -> OccInfo -> CoreExpr -- Binder and rhs - -- For non-recs the binder is alrady tagged - -- with occurrence info + -> Maybe Id -> CoreExpr -- Binder and rhs + -- Just b => non-rec, and alrady tagged with occurrence info + -- Nothing => Rec, no occ info -> (UsageDetails, CoreExpr) -- Returned usage details covers only the RHS, -- and *not* the RULE or INLINE template for the Id -occAnalRhs env occ rhs +occAnalRhs env mb_bndr rhs = occAnal ctxt rhs where - ctxt | certainly_inline = env - | otherwise = rhsCtxt env - -- Note that we generally use an rhsCtxt. This tells the occ anal n - -- that it's looking at an RHS, which has an effect in occAnalApp - -- - -- But there's a problem. Consider - -- x1 = a0 : [] - -- x2 = a1 : x1 - -- x3 = a2 : x2 - -- g = f x3 - -- First time round, it looks as if x1 and x2 occur as an arg of a - -- let-bound constructor ==> give them a many-occurrence. - -- But then x3 is inlined (unconditionally as it happens) and - -- next time round, x2 will be, and the next time round x1 will be - -- Result: multiple simplifier iterations. Sigh. - -- Crude solution: use rhsCtxt for things that occur just once... - - certainly_inline = case occ of - OneOcc in_lam one_br _ -> not in_lam && one_br - _ -> False - + -- See Note [Cascading inlines] + ctxt = case mb_bndr of + Just b | certainly_inline b -> env + _other -> rhsCtxt env + + certainly_inline bndr -- See Note [Cascading inlines] + = case idOccInfo bndr of + OneOcc in_lam one_br _ -> not in_lam && one_br && active && not_stable + _ -> False + where + active = isAlwaysActive (idInlineActivation bndr) + not_stable = not (isStableUnfolding (idUnfolding bndr)) addIdOccs :: UsageDetails -> VarSet -> UsageDetails addIdOccs usage id_set = foldVarSet add usage id_set @@ -833,6 +824,46 @@ addIdOccs usage id_set = foldVarSet add usage id_set -- (Same goes for INLINE.) \end{code} +Note [Cascading inlines] +~~~~~~~~~~~~~~~~~~~~~~~~ +By default we use an rhsCtxt for the RHS of a binding. This tells the +occ anal n that it's looking at an RHS, which has an effect in +occAnalApp. In particular, for constructor applications, it makes +the arguments appear to have NoOccInfo, so that we don't inline into +them. Thus x = f y + k = Just x +we do not want to inline x. + +But there's a problem. Consider + x1 = a0 : [] + x2 = a1 : x1 + x3 = a2 : x2 + g = f x3 +First time round, it looks as if x1 and x2 occur as an arg of a +let-bound constructor ==> give them a many-occurrence. +But then x3 is inlined (unconditionally as it happens) and +next time round, x2 will be, and the next time round x1 will be +Result: multiple simplifier iterations. Sigh. + +So, when analysing the RHS of x3 we notice that x3 will itself +definitely inline the next time round, and so we analyse x3's rhs in +an ordinary context, not rhsCtxt. Hence the "certainly_inline" stuff. + +Annoyingly, we have to approximiate SimplUtils.preInlineUnconditionally. +If we say "yes" when preInlineUnconditionally says "no" the simplifier iterates +indefinitely: + x = f y + k = Just x +inline ==> + k = Just (f y) +float ==> + x1 = f y + k = Just x1 + +This is worse than the slow cascade, so we only want to say "certainly_inline" +if it really is certain. Look at the note with preInlineUnconditionally +for the various clauses. + Expressions ~~~~~~~~~~~ \begin{code} @@ -1115,7 +1146,7 @@ wrapProxy (bndr, rhs_var, co) (body_usg, body) where (body_usg', tagged_bndr) = tagBinder body_usg bndr rhs_usg = unitVarEnv rhs_var NoOccInfo -- We don't need exact info - rhs = mkCoerceI co (Var rhs_var) + rhs = mkCoerceI co (Var (zapIdOccInfo rhs_var)) -- See Note [Zap case binders in proxy bindings] \end{code} @@ -1321,9 +1352,11 @@ extendFvs env s %************************************************************************ \begin{code} -data ProxyEnv - = PE (IdEnv (Id, [(Id,CoercionI)])) VarSet - -- Main env, and its free variables (of both range and domain) +data ProxyEnv -- See Note [ProxyEnv] + = PE (IdEnv -- Domain = scrutinee variables + (Id, -- The scrutinee variable again + [(Id,CoercionI)])) -- The case binders that it maps to + VarSet -- Free variables of both range and domain \end{code} Note [ProxyEnv] @@ -1466,6 +1499,17 @@ From this we want to extract the bindings Notice that later bindings may mention earlier ones, and that we need to go "both ways". +Note [Zap case binders in proxy bindings] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +From the original + case x of cb(dead) { p -> ...x... } +we will get + case x of cb(live) { p -> let x = cb in ...x... } + +Core Lint never expects to find an *occurence* of an Id marked +as Dead, so we must zap the OccInfo on cb before making the +binding x = cb. See Trac #5028. + Historical note [no-case-of-case] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We *used* to suppress the binder-swap in case expressions when @@ -1549,10 +1593,11 @@ extendProxyEnv pe scrut co case_bndr -- Localise the scrut_var before shadowing it; we're making a -- new binding for it, and it might have an External Name, or -- even be a GlobalId; Note [Binder swap on GlobalId scrutinees] - -- Also we don't want any INLILNE or NOINLINE pragmas! + -- Also we don't want any INLINE or NOINLINE pragmas! ----------- type ProxyBind = (Id, Id, CoercionI) + -- (scrut variable, case-binder variable, coercion) getProxies :: OccEnv -> Id -> Bag ProxyBind -- Return a bunch of bindings [...(xi,ei)...]