X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FbasicTypes%2FIdInfo.lhs;h=a3124f359489c50c166d092602a503aa3847304c;hb=41ac7eb30ff99535c24c39efd33e2b65ea458707;hp=b009794fb8a5715d3f497095d75bceb00961a7ab;hpb=55710e16202e985f8e4f910a09dfc2d0298ca255;p=ghc-hetmet.git

diff --git a/compiler/basicTypes/IdInfo.lhs b/compiler/basicTypes/IdInfo.lhs
index b009794..a3124f3 100644
--- a/compiler/basicTypes/IdInfo.lhs
+++ b/compiler/basicTypes/IdInfo.lhs
@@ -464,9 +464,11 @@ type InlinePragInfo = Activation
 %************************************************************************
 
 \begin{code}
--- CoreRules is used only in an idSpecialisation (move to IdInfo?)
 data SpecInfo 
-  = SpecInfo [CoreRule] VarSet	-- Locally-defined free vars of RHSs
+  = SpecInfo 
+	[CoreRule] 
+	VarSet		-- Locally-defined free vars of *both* LHS and RHS of rules
+			-- Note [Rule dependency info]
 
 emptySpecInfo :: SpecInfo
 emptySpecInfo = SpecInfo [] emptyVarSet
@@ -483,6 +485,17 @@ specInfoRules (SpecInfo rules _) = rules
 seqSpecInfo (SpecInfo rules fvs) = seqRules rules `seq` seqVarSet fvs
 \end{code}
 
+Note [Rule dependency info]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+THe VarSet in a SpecInfo is used for dependency analysis in the 
+occurrence analyser.  We must track free vars in *both* lhs and rhs.  Why both?  
+Consider
+	x = y
+ 	RULE f x = 4
+Then if we substitute y for x, we'd better do so in the
+ rule's LHS too, so we'd better ensure the dependency is respsected
+
+
 
 %************************************************************************
 %*									*