diff --git a/src/Lean/Compiler/LCNF/JoinPoints.lean b/src/Lean/Compiler/LCNF/JoinPoints.lean
index d2288555af..76b31f6fd7 100644
--- a/src/Lean/Compiler/LCNF/JoinPoints.lean
+++ b/src/Lean/Compiler/LCNF/JoinPoints.lean
@@ -10,9 +10,6 @@ import Lean.Compiler.LCNF.FVarUtil
 import Lean.Compiler.LCNF.ScopeM
 import Lean.Compiler.LCNF.InferType
 
-set_option warningAsError false
-#exit
-
 namespace Lean.Compiler.LCNF
 
 namespace JoinPointFinder
@@ -75,9 +72,15 @@ private def modifyCandidates (f : HashMap FVarId CandidateInfo → HashMap FVarI
   modify (fun state => {state with candidates := f state.candidates })
 
 /--
-Remove all join point candidates contained in `e`.
+Remove all join point candidates contained in `a`.
 -/
-private partial def removeCandidatesContainedIn (e : Expr) : FindM Unit := do
+private partial def removeCandidatesInArg (a : Arg) : FindM Unit := do
+  forFVarM eraseCandidate a
+
+/--
+Remove all join point candidates contained in `a`.
+-/
+private partial def removeCandidatesInLetExpr (e : LetExpr) : FindM Unit := do
   forFVarM eraseCandidate e
 
 /--
@@ -134,12 +137,12 @@ partial def find (decl : Decl) : CompilerM FindState := do
 where
   go : Code → FindM Unit
   | .let decl k => do
-    match k, decl.value, decl.value.getAppFn with
-    | .return valId, .app .., .fvar fvarId =>
-      decl.value.getAppArgs.forM removeCandidatesContainedIn
+    match k, decl.value with
+    | .return valId, .fvar fvarId args =>
+      args.forM removeCandidatesInArg
       if let some candidateInfo ← findCandidate? fvarId then
         -- Erase candidate that are not fully applied or applied outside of tail position
-        if valId != decl.fvarId || decl.value.getAppNumArgs != candidateInfo.arity then
+        if valId != decl.fvarId || args.size != candidateInfo.arity then
           eraseCandidate fvarId
         -- Out of scope join point candidate handling
         else if let some upperCandidate ← read then
@@ -147,8 +150,8 @@ where
             addDependency fvarId upperCandidate
       else
         eraseCandidate fvarId
-    | _, _, _ =>
-      removeCandidatesContainedIn decl.value
+    | _, _ =>
+      removeCandidatesInLetExpr decl.value
       go k
   | .fun decl k => do
     withReader (fun _ => some decl.fvarId) do
@@ -160,7 +163,7 @@ where
   | .jp decl k => do
     go decl.value
     go k
-  | .jmp _ args => args.forM removeCandidatesContainedIn
+  | .jmp _ args => args.forM removeCandidatesInArg
   | .return val => eraseCandidate val
   | .cases c => do
     eraseCandidate c.discr
@@ -180,17 +183,17 @@ where
   go (code : Code) : ReplaceM Code := do
     match code with
     | .let decl k =>
-      match k, decl.value, decl.value.getAppFn with
-      | .return valId, .app .., (.fvar fvarId) =>
+      match k, decl.value with
+      | .return valId, .fvar fvarId args =>
         if valId == decl.fvarId then
           if (← read).contains fvarId then
             eraseLetDecl decl
-            return .jmp fvarId decl.value.getAppArgs
+            return .jmp fvarId args
           else
             return code
         else
           return code
-      | _, _, _ => return Code.updateLet! code decl (← go k)
+      | _, _ => return Code.updateLet! code decl (← go k)
     | .fun decl k =>
       if let some replacement := (← read).find? decl.fvarId then
         let newDecl := { decl with
@@ -392,12 +395,10 @@ where
   goFVar (fvar : FVarId) : ExtendM FVarId := do
     extendByIfNecessary fvar
     replaceFVar fvar
-  goExpr (e : Expr) : ExtendM Expr :=
-    mapFVarM goFVar e
   go (code : Code) : ExtendM Code := do
     match code with
     | .let decl k =>
-      let decl ← decl.updateValue (← goExpr decl.value)
+      let decl ← decl.updateValue (← mapFVarM goFVar decl.value)
       withNewCandidate decl.fvarId do
         return Code.updateLet! code decl (← go k)
     | .jp decl k =>
@@ -423,7 +424,7 @@ where
       let alts ← cs.alts.mapM visitor
       return Code.updateCases! code cs.resultType discr alts
     | .jmp fn args =>
-      let mut newArgs ← args.mapM goExpr
+      let mut newArgs ← args.mapM (mapFVarM goFVar)
       let additionalArgs := (← get).fvarMap.find! fn |>.toArray |>.map Prod.fst
       if let some _currentJp := (← read).currentJp? then
         let f := fun arg => do
@@ -456,7 +457,8 @@ State for `ReduceAnalysisM`.
 -/
 structure AnalysisState where
   /--
-  Lists of names of arguments of jmps to join points to find duplicates.
+  A map, that for each join point id contains a map from all (so far)
+  duplicated argument ids to the respective duplicate value
   -/
   jpJmpArgs : FVarIdMap FVarSubst := {}
 
@@ -543,13 +545,13 @@ where
         let mut newArgs := knownArgs
         for (param, arg) in decl.params.zip args do
           if let some knownVal := newArgs.find? param.fvarId then
-            if arg != knownVal then
+            if arg.toExpr != knownVal then
               newArgs := newArgs.erase param.fvarId
         modify fun s => { s with jpJmpArgs := s.jpJmpArgs.insert fn newArgs }
       else
         let folder := fun acc (param, arg) => do
           if (← allFVarM (isInJpScope fn) arg) then
-            return acc.insert param.fvarId arg
+            return acc.insert param.fvarId arg.toExpr
           else
             return acc
         let interestingArgs ← decl.params.zip args |>.foldlM (init := {}) folder