(** The proof of semantic preservation is a simulation argument
  based on diagrams of the following form:
<<
           st1 --------------- st2
            |                   |
           t|                  ?|t
            |                   |
            v                   v
           st1'--------------- st2'
>>
  The [match_states] predicate, defined below, captures the precondition
  between states [st1] and [st2], as well as the postcondition between
  [st1'] and [st2'].  One transition in the source code (left) can correspond
  to zero or one transition in the transformed code (right).  The
  "zero transition" case occurs when executing a [Lgoto] instruction
  in the source code that has been removed by tunneling.

  In the definition of [match_states], what changes between the original and
  transformed codes is mainly the control-flow
  (in particular, the current program point [pc]), but also some values
  and memory states, since some [Vundef] values can become more defined
  as a consequence of eliminating useless [Lcond] instructions. *)

Definition tunneled_block (f: function) (b: bblock) :=
  tunnel_block (record_gotos f) b.Definition tunneled_code (f: function) :=
  PTree.map1 (tunneled_block f) (fn_code f).Definition locmap_lessdef (ls1 ls2: locset) : Prop :=
  forall l, Val.lessdef (ls1 l) (ls2 l).Inductive match_stackframes: stackframe -> stackframe -> Prop :=
  | match_stackframes_intro:
      forall f sp ls0 bb tls0,
      locmap_lessdef ls0 tls0 ->
      match_stackframes
         (Stackframe f sp ls0 bb)
         (Stackframe (tunnel_function f) sp tls0 (tunneled_block f bb)).Inductive match_stackframes: stackframe -> stackframe -> Prop :=
  | match_stackframes_intro:
      forall f sp ls0 bb tls0,
      locmap_lessdef ls0 tls0 ->
      match_stackframes
         (Stackframe f sp ls0 bb)
         (Stackframe (tunnel_function f) sp tls0 (tunneled_block f bb)).Inductive match_states: state -> state -> Prop :=
  | match_states_intro:
      forall s f sp pc ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (State s f sp pc ls m)
                   (State ts (tunnel_function f) sp (branch_target f pc) tls tm)
  | match_states_block:
      forall s f sp bb ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Block s f sp bb ls m)
                   (Block ts (tunnel_function f) sp (tunneled_block f bb) tls tm)
  | match_states_interm:
      forall s f sp pc bb ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Block s f sp (Lbranch pc :: bb) ls m)
                   (State ts (tunnel_function f) sp (branch_target f pc) tls tm)
  | match_states_call:
      forall s f ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Callstate s f ls m)
                   (Callstate ts (tunnel_fundef f) tls tm)
  | match_states_return:
      forall s ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Returnstate s ls m)
                   (Returnstate ts tls tm).Inductive match_states: state -> state -> Prop :=
  | match_states_intro:
      forall s f sp pc ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (State s f sp pc ls m)
                   (State ts (tunnel_function f) sp (branch_target f pc) tls tm)
  | match_states_block:
      forall s f sp bb ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Block s f sp bb ls m)
                   (Block ts (tunnel_function f) sp (tunneled_block f bb) tls tm)
  | match_states_interm:
      forall s f sp pc bb ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Block s f sp (Lbranch pc :: bb) ls m)
                   (State ts (tunnel_function f) sp (branch_target f pc) tls tm)
  | match_states_call:
      forall s f ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Callstate s f ls m)
                   (Callstate ts (tunnel_fundef f) tls tm)
  | match_states_return:
      forall s ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Returnstate s ls m)
                   (Returnstate ts tls tm).Inductive match_states: state -> state -> Prop :=
  | match_states_intro:
      forall s f sp pc ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (State s f sp pc ls m)
                   (State ts (tunnel_function f) sp (branch_target f pc) tls tm)
  | match_states_block:
      forall s f sp bb ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Block s f sp bb ls m)
                   (Block ts (tunnel_function f) sp (tunneled_block f bb) tls tm)
  | match_states_interm:
      forall s f sp pc bb ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Block s f sp (Lbranch pc :: bb) ls m)
                   (State ts (tunnel_function f) sp (branch_target f pc) tls tm)
  | match_states_call:
      forall s f ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Callstate s f ls m)
                   (Callstate ts (tunnel_fundef f) tls tm)
  | match_states_return:
      forall s ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Returnstate s ls m)
                   (Returnstate ts tls tm).Inductive match_states: state -> state -> Prop :=
  | match_states_intro:
      forall s f sp pc ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (State s f sp pc ls m)
                   (State ts (tunnel_function f) sp (branch_target f pc) tls tm)
  | match_states_block:
      forall s f sp bb ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Block s f sp bb ls m)
                   (Block ts (tunnel_function f) sp (tunneled_block f bb) tls tm)
  | match_states_interm:
      forall s f sp pc bb ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Block s f sp (Lbranch pc :: bb) ls m)
                   (State ts (tunnel_function f) sp (branch_target f pc) tls tm)
  | match_states_call:
      forall s f ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Callstate s f ls m)
                   (Callstate ts (tunnel_fundef f) tls tm)
  | match_states_return:
      forall s ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Returnstate s ls m)
                   (Returnstate ts tls tm).Inductive match_states: state -> state -> Prop :=
  | match_states_intro:
      forall s f sp pc ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (State s f sp pc ls m)
                   (State ts (tunnel_function f) sp (branch_target f pc) tls tm)
  | match_states_block:
      forall s f sp bb ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Block s f sp bb ls m)
                   (Block ts (tunnel_function f) sp (tunneled_block f bb) tls tm)
  | match_states_interm:
      forall s f sp pc bb ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Block s f sp (Lbranch pc :: bb) ls m)
                   (State ts (tunnel_function f) sp (branch_target f pc) tls tm)
  | match_states_call:
      forall s f ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Callstate s f ls m)
                   (Callstate ts (tunnel_fundef f) tls tm)
  | match_states_return:
      forall s ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Returnstate s ls m)
                   (Returnstate ts tls tm).Inductive match_states: state -> state -> Prop :=
  | match_states_intro:
      forall s f sp pc ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (State s f sp pc ls m)
                   (State ts (tunnel_function f) sp (branch_target f pc) tls tm)
  | match_states_block:
      forall s f sp bb ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Block s f sp bb ls m)
                   (Block ts (tunnel_function f) sp (tunneled_block f bb) tls tm)
  | match_states_interm:
      forall s f sp pc bb ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Block s f sp (Lbranch pc :: bb) ls m)
                   (State ts (tunnel_function f) sp (branch_target f pc) tls tm)
  | match_states_call:
      forall s f ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Callstate s f ls m)
                   (Callstate ts (tunnel_fundef f) tls tm)
  | match_states_return:
      forall s ls m ts tls tm
        (STK: list_forall2 match_stackframes s ts)
        (LS: locmap_lessdef ls tls)
        (MEM: Mem.extends m tm),
      match_states (Returnstate s ls m)
                   (Returnstate ts tls tm).

Lemma return_regs_lessdef: forall caller1 callee1 caller2 callee2, locmap_lessdef caller1 caller2 -> locmap_lessdef callee1 callee2 -> locmap_lessdef (return_regs caller1 callee1) (return_regs caller2 callee2).