Comment fix: use the same variable names in the conclusion as in the premise.

[ghc-hetmet.git] / compiler / simplCore / Simplify.lhs

diff --git a/compiler/simplCore/Simplify.lhs b/compiler/simplCore/Simplify.lhs
index 7c88ad2..d90c5db 100644 (file)
--- a/compiler/simplCore/Simplify.lhs
+++ b/compiler/simplCore/Simplify.lhs
@@ -13,9 +13,9 @@ import SimplMonad
 import Type hiding      ( substTy, extendTvSubst )
 import SimplEnv
 import SimplUtils
 import Type hiding      ( substTy, extendTvSubst )
 import SimplEnv
 import SimplUtils

-import MkId            ( rUNTIME_ERROR_ID )

 import FamInstEnv      ( FamInstEnv )
 import Id
 import FamInstEnv      ( FamInstEnv )
 import Id

+import MkId            ( mkImpossibleExpr, seqId )

 import Var
 import IdInfo
 import Coercion
 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 CoreUtils
 import CoreArity       ( exprArity )
 import Rules            ( lookupRule, getRules )

-import BasicTypes       ( isMarkedStrict )
+import BasicTypes       ( isMarkedStrict, Arity )

 import CostCentre       ( currentCCS )
 import TysPrim          ( realWorldStatePrimTy )
 import PrelInfo         ( realWorldPrimId )
 import CostCentre       ( currentCCS )
 import TysPrim          ( realWorldStatePrimTy )
 import PrelInfo         ( realWorldPrimId )

@@ -871,8 +871,8 @@ simplCast env body co0 cont0
          | (_l1, t1) <- coercionKind co2
                --      e |> (g1 :: S1~L) |> (g2 :: L~T1)
                 -- ==>
          | (_l1, t1) <- coercionKind co2
                --      e |> (g1 :: S1~L) |> (g2 :: L~T1)
                 -- ==>

-                --      e,                       if T1=T2
-                --      e |> (g1 . g2 :: T1~T2)  otherwise
+                --      e,                       if S1=T1
+                --      e |> (g1 . g2 :: S1~T1)  otherwise

                 --
                 -- For example, in the initial form of a worker
                 -- we may find  (coerce T (coerce S (\x.e))) y
                 --
                 -- For example, in the initial form of a worker
                 -- we may find  (coerce T (coerce S (\x.e))) y

@@ -1053,8 +1053,7 @@ simplVar env var cont
 
 completeCall :: SimplEnv -> Id -> SimplCont -> SimplM (SimplEnv, OutExpr)
 completeCall 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
                 -- 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
         -- 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
                  -- The ruleArity says how many args the rule consumed

+           ; Nothing -> do       -- No rules

 
 

-          ; Nothing -> do       -- No rules

 
         ------------- Next try inlining ----------------
 
         ------------- 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
                 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!
 
 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
 %************************************************************************
 %*                                                                      *
                 Rebuilding a cse expression

@@ -1310,12 +1334,13 @@ I don't really know how to improve this situation.
 ---------------------------------------------------------
 --      Eliminate the case if possible
 
 ---------------------------------------------------------
 --      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
 
 --------------------------------------------------
 --      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
 
                                     -- 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
 --------------------------------------------------
 
 
 --------------------------------------------------
 --      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
   = do  {       -- Prepare the continuation;
                 -- The new subst_env is in place
           (env', dup_cont, nodup_cont) <- prepareCaseCont env alts cont

@@ -1390,17 +1431,7 @@ rebuildCase env scrut case_bndr alts cont
         ; (scrut', case_bndr', alts') <- simplAlts env' scrut case_bndr alts dup_cont
 
        -- Check for empty alternatives
         ; (scrut', case_bndr', alts') <- simplAlts env' scrut case_bndr alts dup_cont
 
        -- Check for empty alternatives

-       ; if null alts' then
-               -- This isn't strictly an error, although it is unusual. 
-               -- It's possible that the simplifer might "see" that 
-               -- an inner case has no accessible alternatives before 
-               -- it "sees" that the entire branch of an outer case is 
-               -- inaccessible.  So we simply put an error case here instead.
-           pprTrace "mkCase: null alts" (ppr case_bndr <+> ppr scrut) $
-           let res_ty' = contResultType env' (substTy env' (coreAltsType alts)) dup_cont
-               lit = mkStringLit "Impossible alternative"
-           in return (env', mkApps (Var rUNTIME_ERROR_ID) [Type res_ty', lit])
-
+       ; if null alts' then missingAlt env case_bndr alts cont

          else do
        { case_expr <- mkCase scrut' case_bndr' alts'
 
          else do
        { case_expr <- mkCase scrut' case_bndr' alts'
 

@@ -1687,23 +1718,15 @@ knownCon :: SimplEnv -> OutExpr -> AltCon
 
 knownCon env scrut con args bndr alts cont
   = do  { tick (KnownBranch bndr)
 
 knownCon env scrut con args bndr alts cont
   = do  { tick (KnownBranch bndr)

-        ; knownAlt env scrut args bndr (findAlt con alts) cont }
+        ; case findAlt con alts of
+           Nothing  -> missingAlt env bndr alts cont
+           Just alt -> knownAlt env scrut args bndr alt cont
+       }

 
 

+-------------------

 knownAlt :: SimplEnv -> OutExpr -> [OutExpr]
 knownAlt :: SimplEnv -> OutExpr -> [OutExpr]

-         -> InId -> (AltCon, [CoreBndr], InExpr) -> SimplCont
+         -> InId -> InAlt -> SimplCont

          -> SimplM (SimplEnv, OutExpr)
          -> SimplM (SimplEnv, OutExpr)

-knownAlt env scrut _ bndr (DEFAULT, bs, rhs) cont
-  = ASSERT( null bs )
-    do  { env' <- simplNonRecX env bndr scrut
-                -- This might give rise to a binding with non-atomic args
-                -- like x = Node (f x) (g x)
-                -- but simplNonRecX will atomic-ify it
-        ; simplExprF env' rhs cont }
-
-knownAlt env scrut _ bndr (LitAlt _, bs, rhs) cont
-  = ASSERT( null bs )
-    do  { env' <- simplNonRecX env bndr scrut
-        ; simplExprF env' rhs cont }

 
 knownAlt env scrut the_args bndr (DataAlt dc, bs, rhs) cont
   = do  { let n_drop_tys = length (dataConUnivTyVars dc)
 
 knownAlt env scrut the_args bndr (DataAlt dc, bs, rhs) cont
   = do  { let n_drop_tys = length (dataConUnivTyVars dc)

@@ -1749,6 +1772,25 @@ knownAlt env scrut the_args bndr (DataAlt dc, bs, rhs) cont
     bind_args _ _ _ =
       pprPanic "bind_args" $ ppr dc $$ ppr bs $$ ppr the_args $$
                              text "scrut:" <+> ppr scrut
     bind_args _ _ _ =
       pprPanic "bind_args" $ ppr dc $$ ppr bs $$ ppr the_args $$
                              text "scrut:" <+> ppr scrut

+
+knownAlt env scrut _ bndr (_, bs, rhs) cont
+  = ASSERT( null bs )    -- Works for LitAlt and DEFAULT
+    do  { env' <- simplNonRecX env bndr scrut
+        ; simplExprF env' rhs cont }
+
+
+-------------------
+missingAlt :: SimplEnv -> Id -> [InAlt] -> SimplCont -> SimplM (SimplEnv, OutExpr)
+               -- This isn't strictly an error, although it is unusual. 
+               -- It's possible that the simplifer might "see" that 
+               -- an inner case has no accessible alternatives before 
+               -- it "sees" that the entire branch of an outer case is 
+               -- inaccessible.  So we simply put an error case here instead.
+missingAlt env case_bndr alts cont
+  = WARN( True, ptext (sLit "missingAlt") <+> ppr case_bndr )
+    return (env, mkImpossibleExpr res_ty)
+  where
+    res_ty = contResultType env (substTy env (coreAltsType alts)) cont

 \end{code}
 
 
 \end{code}
 
 

@@ -1912,7 +1954,7 @@ we'd lose that when zapping the subst-env.  We could have a per-alt subst-env,
 but zapping it (as we do in mkDupableCont, the Select case) is safe, and
 at worst delays the join-point inlining.
 
 but zapping it (as we do in mkDupableCont, the Select case) is safe, and
 at worst delays the join-point inlining.
 

-Note [Small alterantive rhs]
+Note [Small alternative 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
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 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