diff --git a/library/init/lean/compiler/ir/unreachbranches.lean b/library/init/lean/compiler/ir/unreachbranches.lean
index 9a725b5308..bf52c896f3 100644
--- a/library/init/lean/compiler/ir/unreachbranches.lean
+++ b/library/init/lean/compiler/ir/unreachbranches.lean
@@ -5,6 +5,7 @@ Authors: Leonardo de Moura
 -/
 prelude
 import init.control.reader
+import init.data.option
 import init.lean.compiler.ir.format
 import init.lean.compiler.ir.basic
 
@@ -85,26 +86,26 @@ functionSummariesExt.addEntry env (fid, v)
 def getFunctionSummary (env : Environment) (fid : FunId) : Option Value :=
 (functionSummariesExt.getState env).find fid
 
-def Assignment := PHashMap VarId Value
+abbrev Assignment := HashMap VarId Value
 
 structure InterpContext :=
-(currFn : Name)
-(env    : Environment)
-(lctx   : LocalContext)
-
-abbrev FunMap := HashMap FunId Value
+(currFnIdx : Nat := 0)
+(decls     : Array Decl)
+(env       : Environment)
+(lctx      : LocalContext := {})
 
 structure InterpState :=
-(assignment : Assignment)
-(funMap     : FunMap)
+(assignments : Array Assignment)
+(funVals     : PArray Value) -- we take snapshots during fixpoint computations
 
 abbrev M := ReaderT InterpContext (State InterpState)
 
 open Value
 
 def findVarValue (x : VarId) : M Value :=
-do s ← get;
-   match s.assignment.find x with
+do ctx ← read;
+   s ← get;
+   match (s.assignments.get! ctx.currFnIdx).find x with
    | some v => pure v
    | none   => pure top
 
@@ -115,7 +116,8 @@ match arg with
 
 def updateVarAssignment (x : VarId) (v : Value) : M Unit :=
 do v' ← findVarValue x;
-   modify $ fun s => { assignment := s.assignment.insert x (merge v v'), .. s }
+   ctx ← read;
+   modify $ fun s => { assignments := s.assignments.modify ctx.currFnIdx $ fun a => a.insert x (merge v v'), .. s }
 
 partial def projValue : Value → Nat → Value
 | ctor _ vs, i => vs.getD i bot
@@ -129,7 +131,11 @@ def interpExpr : Expr → M Value
   ctx ← read;
   match getFunctionSummary ctx.env fid with
   | some v => pure v
-  | none   => pure top
+  | none   => do
+    s ← get;
+    match ctx.decls.findIdx? (fun decl => decl.name == fid) with
+    | some idx => pure $ s.funVals.get! idx
+    | none     => pure top
 | _ => pure top
 
 partial def containsCtor : Value → CtorInfo → Bool
@@ -140,10 +146,26 @@ partial def containsCtor : Value → CtorInfo → Bool
 
 def updateCurrFnSummary (v : Value) : M Unit :=
 do ctx ← read;
-   s   ← get;
-   let currFn := ctx.currFn;
-   let v' := (s.funMap.find currFn).getOrElse bot;
-   modify $ fun s => { funMap := s.funMap.insert currFn (merge v v'), .. s }
+   let currFnIdx := ctx.currFnIdx;
+   s ← get;
+   modify $ fun s => { funVals := s.funVals.modify currFnIdx (fun v' => merge v v'), .. s }
+
+
+/-- Return true if the assignment of at least one parameter has been updated. -/
+def updateJPParamsAssignment (ys : Array Param) (xs : Array Arg) : M Bool :=
+do ctx ← read;
+   let currFnIdx := ctx.currFnIdx;
+   ys.size.mfold (fun i r => do
+     let y := ys.get! i;
+     let x := xs.get! i;
+     yVal ← findVarValue y.x;
+     xVal ← findArgValue x;
+     let newVal := merge yVal xVal;
+     if newVal == yVal then pure r
+     else do
+       modify $ fun s => { assignments := s.assignments.modify currFnIdx $ fun a => a.insert y.x newVal, .. s };
+       pure true)
+     false
 
 partial def interpFnBody : FnBody → M Unit
 | FnBody.vdecl x _ e b => do
@@ -164,10 +186,42 @@ partial def interpFnBody : FnBody → M Unit
   updateCurrFnSummary v
 | FnBody.jmp j xs => do
   ctx ← read;
-  -- TODO
-  pure ()
+  let ys := (ctx.lctx.getJPParams j).get!;
+  updated ← updateJPParamsAssignment ys xs;
+  when updated $
+    interpFnBody $ (ctx.lctx.getJPBody j).get!
 | e => unless (e.isTerminal) $ interpFnBody e.body
 
+def inferStep : M Bool :=
+do ctx ← read;
+   ctx.decls.size.mfold (fun idx modified => do
+     match ctx.decls.get! idx with
+     | Decl.fdecl _ _ _ b => do
+       s ← get;
+       let currVals := s.funVals.get! idx;
+       adaptReader (fun (ctx : InterpContext) => { currFnIdx := idx, .. ctx }) $
+         interpFnBody b;
+       s ← get;
+       let newVals := s.funVals.get! idx;
+       -- TODO: apply widening
+       pure (modified || currVals != newVals)
+     | Decl.extern _ _ _ _ => pure modified)
+     false
+
+partial def inferMain : Unit → M Unit
+| _ => do
+  modified ← inferStep;
+  if modified then inferMain () else pure ()
+
+def infer (env : Environment) (decls : Array Decl) : Environment :=
+let assignments : Array Assignment := decls.map $ fun _ => {};
+let funVals := mkPArray decls.size bot;
+let ctx : InterpContext := { decls := decls, env := env };
+let s : InterpState := { assignments := assignments, funVals := funVals };
+let (_, s) := (inferMain () ctx).run s;
+let funVals := s.funVals;
+decls.size.fold (fun i env => addFunctionSummary env (decls.get! i).name (funVals.get! i)) env
+
 end UnreachableBranches
 end IR
 end Lean