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-rw-r--r--compiler/simplCore/Simplify.lhs133
1 files changed, 87 insertions, 46 deletions
diff --git a/compiler/simplCore/Simplify.lhs b/compiler/simplCore/Simplify.lhs
index 974ec58d03..b38bdc8a7b 100644
--- a/compiler/simplCore/Simplify.lhs
+++ b/compiler/simplCore/Simplify.lhs
@@ -15,7 +15,7 @@ import SimplEnv
import SimplUtils
import FamInstEnv ( FamInstEnv )
import Id
-import MkId ( mkImpossibleExpr )
+import MkId ( mkImpossibleExpr, seqId )
import Var
import IdInfo
import Coercion
@@ -28,7 +28,7 @@ import CoreUnfold ( mkUnfolding, callSiteInline, CallCtxt(..) )
import CoreUtils
import CoreArity ( exprArity )
import Rules ( lookupRule, getRules )
-import BasicTypes ( isMarkedStrict )
+import BasicTypes ( isMarkedStrict, Arity )
import CostCentre ( currentCCS )
import TysPrim ( realWorldStatePrimTy )
import PrelInfo ( realWorldPrimId )
@@ -1053,8 +1053,7 @@ simplVar env var cont
completeCall :: SimplEnv -> Id -> SimplCont -> SimplM (SimplEnv, OutExpr)
completeCall env var cont
- = do { dflags <- getDOptsSmpl
- ; let (args,call_cont) = contArgs cont
+ = do { let (args,call_cont) = contArgs cont
-- The args are OutExprs, obtained by *lazily* substituting
-- in the args found in cont. These args are only examined
-- to limited depth (unless a rule fires). But we must do
@@ -1070,45 +1069,18 @@ completeCall env var cont
-- 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
- --
- -- Note [Rules for recursive functions]
- -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- -- 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
- ; rule_base <- getSimplRules
- ; let in_scope = getInScope env
- rules = getRules rule_base var
- maybe_rule = case activeRule dflags env of
- Nothing -> Nothing -- No rules apply
- Just act_fn -> lookupRule act_fn in_scope
- var args rules
- ; case maybe_rule of {
- Just (rule, rule_rhs) -> do
- tick (RuleFired (ru_name rule))
- (if dopt Opt_D_dump_rule_firings dflags then
- pprTrace "Rule fired" (vcat [
- text "Rule:" <+> ftext (ru_name rule),
- text "Before:" <+> ppr var <+> sep (map pprParendExpr args),
- text "After: " <+> pprCoreExpr rule_rhs,
- text "Cont: " <+> ppr call_cont])
- else
- id) $
- simplExprF env rule_rhs (dropArgs (ruleArity rule) cont)
+ --
+ -- See also Note [Rules for recursive functions]
+ ; mb_rule <- tryRules env var args call_cont
+ ; case mb_rule of {
+ Just (n_args, rule_rhs) -> simplExprF env rule_rhs (dropArgs n_args cont) ;
-- The ruleArity says how many args the rule consumed
+ ; Nothing -> do -- No rules
- ; Nothing -> do -- No rules
------------- Next try inlining ----------------
- { let arg_infos = [interestingArg arg | arg <- args, isValArg arg]
+ { dflags <- getDOptsSmpl
+ ; let arg_infos = [interestingArg arg | arg <- args, isValArg arg]
n_val_args = length arg_infos
interesting_cont = interestingCallContext call_cont
active_inline = activeInline env var
@@ -1214,6 +1186,58 @@ 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!
+
+%************************************************************************
+%* *
+ Rewrite rules
+%* *
+%************************************************************************
+
+\begin{code}
+tryRules :: SimplEnv -> Id -> [OutExpr] -> SimplCont
+ -> SimplM (Maybe (Arity, CoreExpr)) -- The arity is the number of
+ -- args consumed by the rule
+tryRules env fn args call_cont
+ = do { dflags <- getDOptsSmpl
+ ; rule_base <- getSimplRules
+ ; let in_scope = getInScope env
+ rules = getRules rule_base fn
+ maybe_rule = case activeRule dflags env of
+ Nothing -> Nothing -- No rules apply
+ Just act_fn -> lookupRule act_fn in_scope
+ fn args rules
+ ; case (rules, maybe_rule) of {
+ ([], _) -> return Nothing ;
+ (_, Nothing) -> return Nothing ;
+ (_, Just (rule, rule_rhs)) -> do
+
+ { tick (RuleFired (ru_name rule))
+ ; (if dopt Opt_D_dump_rule_firings dflags then
+ pprTrace "Rule fired" (vcat [
+ text "Rule:" <+> ftext (ru_name rule),
+ text "Before:" <+> ppr fn <+> sep (map pprParendExpr args),
+ text "After: " <+> pprCoreExpr rule_rhs,
+ text "Cont: " <+> ppr call_cont])
+ else
+ id) $
+ return (Just (ruleArity rule, rule_rhs)) }}}
+\end{code}
+
+Note [Rules for recursive functions]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+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
+
+
%************************************************************************
%* *
Rebuilding a cse expression
@@ -1310,12 +1334,13 @@ I don't really know how to improve this situation.
---------------------------------------------------------
-- Eliminate the case if possible
-rebuildCase :: SimplEnv
- -> OutExpr -- Scrutinee
- -> InId -- Case binder
- -> [InAlt] -- Alternatives (inceasing order)
- -> SimplCont
- -> SimplM (SimplEnv, OutExpr)
+rebuildCase, reallyRebuildCase
+ :: SimplEnv
+ -> OutExpr -- Scrutinee
+ -> InId -- Case binder
+ -> [InAlt] -- Alternatives (inceasing order)
+ -> SimplCont
+ -> SimplM (SimplEnv, OutExpr)
--------------------------------------------------
-- 1. Eliminate the case if there's a known constructor
@@ -1376,12 +1401,28 @@ rebuildCase env scrut case_bndr [(_, bndrs, rhs)] cont
-- exprOkForSpeculation was intended for.
var_demanded_later _ = False
+rebuildCase env scrut case_bndr alts@[(_, bndrs, rhs)] cont
+ | all isDeadBinder (case_bndr : bndrs) -- So this is just 'seq'
+ = -- For this case, see Note [Rules for seq] in MkId
+ do { let rhs' = substExpr env rhs
+ out_args = [Type (substTy env (idType case_bndr)),
+ Type (exprType rhs'), scrut, rhs']
+ -- Lazily evaluated, so we don't do most of this
+ ; mb_rule <- tryRules env seqId out_args cont
+ ; case mb_rule of
+ Just (n_args, res) -> simplExprF (zapSubstEnv env)
+ (mkApps res (drop n_args out_args))
+ cont
+ Nothing -> reallyRebuildCase env scrut case_bndr alts cont }
+
+rebuildCase env scrut case_bndr alts cont
+ = reallyRebuildCase env scrut case_bndr alts cont
--------------------------------------------------
-- 3. Catch-all case
--------------------------------------------------
-rebuildCase env scrut case_bndr alts cont
+reallyRebuildCase env scrut case_bndr alts cont
= do { -- Prepare the continuation;
-- The new subst_env is in place
(env', dup_cont, nodup_cont) <- prepareCaseCont env alts cont
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