Robustify the treatement of DFunUnfolding

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

diff --git a/compiler/coreSyn/CoreFVs.lhs b/compiler/coreSyn/CoreFVs.lhs
index f94f61d..46c21b2 100644 (file)
--- a/compiler/coreSyn/CoreFVs.lhs
+++ b/compiler/coreSyn/CoreFVs.lhs
@@ -416,12 +416,16 @@ idRuleRhsVars id = foldr (unionVarSet . ruleRhsFreeVars)
 idUnfoldingVars :: Id -> VarSet
 -- Produce free vars for an unfolding, but NOT for an ordinary
 -- (non-inline) unfolding, since it is a dup of the rhs
+-- and we'll get exponential behaviour if we look at both unf and rhs!
+-- But do look at the *real* unfolding, even for loop breakers, else
+-- we might get out-of-scope variables
 idUnfoldingVars id
-  = case idUnfolding id of
-      CoreUnfolding { uf_tmpl = rhs, uf_guidance = InlineRule {} }
-                          -> exprFreeVars rhs
-      DFunUnfolding _ args -> exprsFreeVars args
-      _                    -> emptyVarSet
+  = case realIdUnfolding id of
+      CoreUnfolding { uf_tmpl = rhs, uf_src = src }
+                            | isInlineRuleSource src
+                            -> exprFreeVars rhs
+      DFunUnfolding _ _ args -> exprsFreeVars args
+      _                      -> emptyVarSet
 \end{code}