[project @ 1997-05-26 03:12:48 by sof]

Updated switchOffInlining

diff --git a/ghc/compiler/simplCore/SimplEnv.lhs b/ghc/compiler/simplCore/SimplEnv.lhs
index 346d443..6656d56 100644 (file)
--- a/ghc/compiler/simplCore/SimplEnv.lhs
+++ b/ghc/compiler/simplCore/SimplEnv.lhs
@@ -72,9 +72,8 @@ import Literal                ( isNoRepLit, Literal{-instances-} )
 import Maybes          ( maybeToBool, expectJust )
 import Name            ( isLocallyDefined )
 import OccurAnal       ( occurAnalyseExpr )
-import Outputable      ( Outputable(..){-instances-} )
+import Outputable      ( PprStyle(..), Outputable(..){-instances-} )
 import PprCore         -- various instances
-import PprStyle                ( PprStyle(..) )
 import PprType         ( GenType, GenTyVar )
 import Pretty
 import Type            ( eqTy, applyTypeEnvToTy, SYN_IE(Type) )
@@ -184,13 +183,6 @@ getSimplIntSwitch chkr switch
   = expectJust "getSimplIntSwitch" (intSwitchSet chkr switch)
 
        -- Crude, but simple
-switchOffInlining :: SimplEnv -> SimplEnv
-switchOffInlining (SimplEnv chkr encl_cc ty_env in_id_env out_id_env con_apps)
-  = SimplEnv chkr' encl_cc ty_env in_id_env out_id_env con_apps
-  where
-    chkr' EssentialUnfoldingsOnly = SwBool True
-    chkr' other                          = chkr other
-
 setCaseScrutinee :: SimplEnv -> SimplEnv
 setCaseScrutinee (SimplEnv chkr encl_cc ty_env in_id_env out_id_env con_apps)
   = SimplEnv chkr' encl_cc ty_env in_id_env out_id_env con_apps
@@ -199,6 +191,44 @@ setCaseScrutinee (SimplEnv chkr encl_cc ty_env in_id_env out_id_env con_apps)
     chkr' other                     = chkr other
 \end{code}
 
+@switchOffInlining@ is used to prepare the environment for simplifying
+the RHS of an Id that's marked with an INLINE pragma.  It is going to
+be inlined wherever they are used, and then all the inlining will take
+effect.  Meanwhile, there isn't much point in doing anything to the
+as-yet-un-INLINEd rhs.  Furthremore, it's very important to switch off
+inlining!  because
+       (a) not doing so will inline a worker straight back into its wrapper!
+
+and    (b) Consider the following example 
+               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 will be inlined inside g,
+       and thence copied multiple times when g is inlined.
+
+       Andy disagrees! Example:
+               all xs = foldr (&&) True xs
+               any p = all . map p  {-# INLINE any #-}
+       
+       Problem: any won't get deforested, and so if it's exported and
+       the importer doesn't use the inlining, (eg passes it as an arg)
+       then we won't get deforestation at all.
+       We havn't solved this problem yet!
+
+We prepare the envt by simply discarding the out_id_env, which has
+all the unfolding info. At one point we did it by modifying the chkr so
+that it said "EssentialUnfoldingsOnly", but that prevented legitmate, and important,
+simplifications happening in the body of the RHS.
+
+\begin{code}
+switchOffInlining :: SimplEnv -> SimplEnv
+switchOffInlining (SimplEnv chkr encl_cc ty_env in_id_env out_id_env con_apps)
+  = SimplEnv chkr encl_cc ty_env in_id_env nullIdEnv nullConApps
+\end{code}
+
 %************************************************************************
 %*                                                                     *
 \subsubsection{The ``enclosing cost-centre''}