fix: if inlined code returns a function and has more than one exit point, create an auxiliary function instead of a join point that takes a closure as argument

src/Lean/Compiler/LCNF/Simp/Main.lean

@@ -136,35 +136,41 @@ partial def inlineApp? (letDecl : LetDecl) (k : Code) : SimpM (Option Code) := d
       simp code
     else
       let code ← simp code
+      let simpK (result : FVarId) : SimpM Code := do
+        /- `result` contains the result of the inlined code -/
+        if numArgs > info.arity then
+          let decl ← mkAuxLetDecl (mkAppN (.fvar result) info.args[info.arity:])
+          addFVarSubst fvarId decl.fvarId
+          simp (.let decl k)
+        else
+          addFVarSubst fvarId result
+          simp k
       if oneExitPointQuick code then
         -- TODO: if `k` is small, we should also inline it here
         markSimplified
         code.bind fun fvarId' => do
           markUsedFVar fvarId'
-          /- fvarId' is the result of the computation -/
-          if numArgs > info.arity then
-            let decl ← mkAuxLetDecl (mkAppN (.fvar fvarId') info.args[info.arity:])
-            addFVarSubst fvarId decl.fvarId
-            simp (.let decl k)
-          else
-            addFVarSubst fvarId fvarId'
-            simp k
+          simpK fvarId'
       -- else if info.ifReduce then
       --  eraseCode code
       --  return none
       else
         markSimplified
-        let jpParam ← mkAuxParam expectedType
-        let jpValue ← if numArgs > info.arity then
-          let decl ← mkAuxLetDecl (mkAppN (.fvar jpParam.fvarId) info.args[info.arity:])
-          addFVarSubst fvarId decl.fvarId
-          simp (.let decl k)
+        if expectedType.headBeta.isForall then
+          /-
+          If `code` returns a function, we create an auxiliary local function declaration (and eta-expand it)
+          instead of creating a joinpoint that takes a closure as an argument.
+          -/
+          let auxFunDecl ← mkAuxFunDecl #[] code
+          let auxFunDecl ← auxFunDecl.etaExpand
+          let k ← simpK auxFunDecl.fvarId
+          attachCodeDecls #[.fun auxFunDecl] k
         else
-          addFVarSubst fvarId jpParam.fvarId
-          simp k
-        let jpDecl ← mkAuxJpDecl #[jpParam] jpValue
-        let code ← code.bind fun fvarId => return .jmp jpDecl.fvarId #[.fvar fvarId]
-        return Code.jp jpDecl code
+          let jpParam ← mkAuxParam expectedType
+          let jpValue ← simpK jpParam.fvarId
+          let jpDecl ← mkAuxJpDecl #[jpParam] jpValue
+          let code ← code.bind fun fvarId => return .jmp jpDecl.fvarId #[.fvar fvarId]
+          return Code.jp jpDecl code
 
 /--
 Simplify the given local function declaration.