More work on the simplifier's inlining strategies

[ghc-hetmet.git] / compiler / coreSyn / CoreSubst.lhs

diff --git a/compiler/coreSyn/CoreSubst.lhs b/compiler/coreSyn/CoreSubst.lhs
index 4b42c0d..b5d7fde 100644 (file)
--- a/compiler/coreSyn/CoreSubst.lhs
+++ b/compiler/coreSyn/CoreSubst.lhs
@@ -13,7 +13,7 @@ module CoreSubst (
         -- ** Substituting into expressions and related types
        deShadowBinds, substSpec, substRulesForImportedIds,
        substTy, substExpr, substBind, substUnfolding,
-       substInlineRuleInfo, lookupIdSubst, lookupTvSubst, substIdOcc,
+       substUnfoldingSource, lookupIdSubst, lookupTvSubst, substIdOcc,
 
         -- ** Operations on substitutions
        emptySubst, mkEmptySubst, mkSubst, mkOpenSubst, substInScope, isEmptySubst, 
@@ -507,30 +507,39 @@ substUnfolding :: Subst -> Unfolding -> Unfolding
 substUnfolding subst (DFunUnfolding con args)
   = DFunUnfolding con (map (substExpr subst) args)
 
-substUnfolding subst unf@(CoreUnfolding { uf_tmpl = tmpl, uf_guidance = guide@(InlineRule {}) })
+substUnfolding subst unf@(CoreUnfolding { uf_tmpl = tmpl, uf_src = src })
        -- Retain an InlineRule!
+  | not (isInlineRuleSource src)  -- Always zap a CoreUnfolding, to save substitution work
+  = NoUnfolding
+  | otherwise                     -- But keep an InlineRule!
   = seqExpr new_tmpl `seq` 
-    new_mb_wkr `seq`
-    unf { uf_tmpl = new_tmpl, uf_guidance = guide { ug_ir_info = new_mb_wkr } }
+    new_src `seq`
+    unf { uf_tmpl = new_tmpl, uf_src = new_src }
   where
-    new_tmpl   = substExpr subst tmpl
-    new_mb_wkr = substInlineRuleGuidance subst (ug_ir_info guide)
+    new_tmpl = substExpr subst tmpl
+    new_src  = substUnfoldingSource subst src
 
-substUnfolding _ (CoreUnfolding {}) = NoUnfolding      -- Discard
-       -- Always zap a CoreUnfolding, to save substitution work
-
-substUnfolding _ unf = unf     -- Otherwise no substitution to do
+substUnfolding _ unf = unf     -- NoUnfolding, OtherCon
 
 -------------------
-substInlineRuleGuidance :: Subst -> InlineRuleInfo -> InlineRuleInfo
-substInlineRuleGuidance subst (InlWrapper wkr)
-  = case lookupIdSubst subst wkr of
-      Var w1 -> InlWrapper w1
-      other  -> WARN( not (exprIsTrivial other), text "CoreSubst.substWorker:" <+> ppr wkr )
-               InlUnSat   -- Worker has got substituted away altogether
-                          -- (This can happen if it's trivial, via
-                          --  postInlineUnconditionally, hence only warning)
-substInlineRuleGuidance _ info = info
+substUnfoldingSource :: Subst -> UnfoldingSource -> UnfoldingSource
+substUnfoldingSource (Subst in_scope ids _) (InlineWrapper wkr)
+  | Just wkr_expr <- lookupVarEnv ids wkr 
+  = case wkr_expr of
+      Var w1 -> InlineWrapper w1
+      _other -> WARN( True, text "Interesting! CoreSubst.substWorker1:" <+> ppr wkr 
+                            <+> equals <+> ppr wkr_expr )   -- Note [Worker inlining]
+                InlineRule    -- It's not a wrapper any more, but still inline it!
+
+  | Just w1  <- lookupInScope in_scope wkr = InlineWrapper w1
+  | otherwise = WARN( True, text "Interesting! CoreSubst.substWorker2:" <+> ppr wkr )
+               -- This can legitimately happen.  The worker has been inlined and
+               -- dropped as dead code, because we don't treat the UnfoldingSource
+               -- as an "occurrence".
+                -- Note [Worker inlining]
+               InlineRule
+
+substUnfoldingSource _ src = src
 
 ------------------
 substIdOcc :: Subst -> Id -> Id
@@ -584,6 +593,18 @@ substVarSet subst fvs
        | otherwise = Type.tyVarsOfType (lookupTvSubst subst fv)
 \end{code}
 
+Note [Worker inlining]
+~~~~~~~~~~~~~~~~~~~~~~
+A worker can get sustituted away entirely.
+       - it might be trivial
+       - it might simply be very small
+We do not treat an InlWrapper as an 'occurrence' in the occurence 
+analyser, so it's possible that the worker is not even in scope any more.
+
+In all all these cases we simply drop the special case, returning to
+InlVanilla.  The WARN is just so I can see if it happens a lot.
+
+
 %************************************************************************
 %*                                                                     *
        The Very Simple Optimiser