path: root/backend/KillUselessMovesproof.v

(* *************************************************************)
(*                                                             *)
(*             The Compcert verified compiler                  *)
(*                                                             *)
(*           David Monniaux     CNRS, VERIMAG                  *)
(*                                                             *)
(*  Copyright VERIMAG. All rights reserved.                    *)
(*  This file is distributed under the terms of the INRIA      *)
(*  Non-Commercial License Agreement.                          *)
(*                                                             *)
(* *************************************************************)

Require Import Axioms.
Require Import FunInd.
Require Import Coqlib Maps Errors Integers Floats Lattice Kildall.
Require Import AST Linking.
Require Import Values Memory Globalenvs Events Smallstep.
Require Import Registers Op RTL.
Require Import KillUselessMoves.


Definition match_prog (p tp: RTL.program) :=
  match_program (fun ctx f tf => tf = transf_fundef f) eq p tp.

Lemma transf_program_match:
  forall p, match_prog p (transf_program p).
Proof.
  intros. eapply match_transform_program; eauto.
Qed.

Section PRESERVATION.

Variables prog tprog: program.
Hypothesis TRANSL: match_prog prog tprog.
Let ge := Genv.globalenv prog.
Let tge := Genv.globalenv tprog.

Lemma functions_translated:
  forall v f,
  Genv.find_funct ge v = Some f ->
  Genv.find_funct tge v = Some (transf_fundef f).
Proof (Genv.find_funct_transf TRANSL).

Lemma function_ptr_translated:
  forall v f,
  Genv.find_funct_ptr ge v = Some f ->
  Genv.find_funct_ptr tge v = Some (transf_fundef f).
Proof (Genv.find_funct_ptr_transf TRANSL).

Lemma symbols_preserved:
  forall id,
  Genv.find_symbol tge id = Genv.find_symbol ge id.
Proof (Genv.find_symbol_transf TRANSL).

Lemma senv_preserved:
  Senv.equiv ge tge.
Proof (Genv.senv_transf TRANSL).

Lemma sig_preserved:
  forall f, funsig (transf_fundef f) = funsig f.
Proof.
  destruct f; reflexivity.
Qed.

Lemma find_function_translated:
  forall ros rs fd,
  find_function ge ros rs = Some fd ->
  find_function tge ros rs = Some (transf_fundef fd).
Proof.
  unfold find_function; intros. destruct ros as [r|id].
  eapply functions_translated; eauto.
  rewrite symbols_preserved. destruct (Genv.find_symbol ge id); try congruence.
  eapply function_ptr_translated; eauto.
Qed.

Lemma transf_function_at:
  forall f pc i,
  f.(fn_code)!pc = Some i ->
  (transf_function f).(fn_code)!pc = Some(transf_instr pc i).
Proof.
  intros until i. intro Hcode.
  unfold transf_function; simpl.
  rewrite PTree.gmap.
  unfold option_map.
  rewrite Hcode.
  reflexivity.
Qed.

Ltac TR_AT :=
  match goal with
  | [ A: (fn_code _)!_ = Some _ |- _ ] =>
        generalize (transf_function_at _ _ _ A); intros
  end.

Section SAME_RS.
  Context {A : Type}.
  
  Definition same_rs (rs rs' : Regmap.t A) :=
    forall x, rs # x = rs' # x.

  Lemma same_rs_refl : forall rs, same_rs rs rs.
  Proof.
    unfold same_rs.
    reflexivity.
  Qed.

  Lemma same_rs_comm : forall rs rs', (same_rs rs rs') -> (same_rs rs' rs).
  Proof.
    unfold same_rs.
    congruence.
  Qed.

  Lemma same_rs_trans : forall rs1 rs2 rs3,
      (same_rs rs1 rs2) -> (same_rs rs2 rs3) -> (same_rs rs1 rs3).
  Proof.
    unfold same_rs.
    congruence.
  Qed.

  Lemma same_rs_idem_write : forall rs r,
      (same_rs rs (rs # r <- (rs # r))).
  Proof.
    unfold same_rs.
    intros.
    rewrite Regmap.gsident.
    reflexivity.
  Qed.

  Lemma same_rs_read:
    forall rs rs' r, (same_rs rs rs') -> rs # r = rs' # r.
  Proof.
    unfold same_rs.
    auto.
  Qed.
  
  Lemma same_rs_subst:
    forall rs rs' l, (same_rs rs rs') -> rs ## l = rs' ## l.
  Proof.
    induction l; cbn; intuition congruence.
  Qed.

  Lemma same_rs_write: forall rs rs' r x,
      (same_rs rs rs') -> (same_rs (rs # r <- x) (rs' # r <- x)).
  Proof.
    unfold same_rs.
    intros.
    destruct (peq r x0).
    { subst x0.
      rewrite Regmap.gss. rewrite Regmap.gss.
      reflexivity.
    }
    rewrite Regmap.gso by congruence.
    rewrite Regmap.gso by congruence.
    auto.
  Qed.

  Lemma same_rs_setres:
    forall rs rs' (SAME: same_rs rs rs') res vres,
      same_rs (regmap_setres res vres rs) (regmap_setres res vres rs').
  Proof.
    induction res; cbn; auto using same_rs_write.
  Qed.
End SAME_RS.

Lemma same_find_function: forall tge rs rs' (SAME: same_rs rs rs') ros,
  find_function tge ros rs = find_function tge ros rs'.
Proof.
  destruct ros; cbn.
  { rewrite (same_rs_read rs rs' r SAME).
    reflexivity. }
  reflexivity.
Qed.

Inductive match_frames: RTL.stackframe -> RTL.stackframe -> Prop :=
| match_frames_intro: forall res f sp pc rs rs' (SAME : same_rs rs rs'),
    match_frames (Stackframe res f sp pc rs)
                 (Stackframe res (transf_function f) sp pc rs').

Inductive match_states: RTL.state -> RTL.state -> Prop :=
  | match_regular_states: forall stk f sp pc rs rs' m stk'
        (SAME: same_rs rs rs')
        (STACKS: list_forall2 match_frames stk stk'),
      match_states (State stk f sp pc rs m)
                   (State stk' (transf_function f) sp pc rs' m)
  | match_callstates: forall stk f args m stk'
        (STACKS: list_forall2 match_frames stk stk'),
      match_states (Callstate stk f args m)
                   (Callstate stk' (transf_fundef f) args m)
  | match_returnstates: forall stk v m stk'
        (STACKS: list_forall2 match_frames stk stk'),
      match_states (Returnstate stk v m)
                   (Returnstate stk' v m).

Lemma step_simulation:
  forall S1 t S2, RTL.step ge S1 t S2 ->
  forall S1', match_states S1 S1' ->
  exists S2', RTL.step tge S1' t S2' /\ match_states S2 S2'.
Proof.
  induction 1; intros S1' MS; inv MS; try TR_AT.
- (* nop *)
  econstructor; split. eapply exec_Inop; eauto.
  constructor; auto.
- (* op *)
  cbn in H1.
  destruct (_ && _) eqn:IS_MOVE in H1.
  {
    destruct eq_operation in IS_MOVE. 2: discriminate.
    destruct list_eq_dec in IS_MOVE. 2: discriminate.
    subst op. subst args.
    clear IS_MOVE.
    cbn in H0.
    inv H0.
    econstructor; split.
    { eapply exec_Inop; eauto. }
    constructor.
    2: assumption.
    eapply same_rs_trans.
    { apply same_rs_comm.
      apply same_rs_idem_write.
    }
    assumption.
  }
  econstructor; split.
  eapply exec_Iop with (v := v); eauto.
  rewrite <- H0.
  rewrite (same_rs_subst rs rs' args SAME).
  apply eval_operation_preserved. exact symbols_preserved.
  constructor; auto using same_rs_write.
(* load *)
- inv H0.
  + econstructor; split.
    assert (eval_addressing tge sp addr rs' ## args = Some a).
    { rewrite <- EVAL.
      rewrite (same_rs_subst rs rs' args SAME).
      apply eval_addressing_preserved. exact symbols_preserved.
    }
    eapply exec_Iload; eauto. eapply has_loaded_normal; eauto.
    constructor; auto using same_rs_write.
  + destruct (eval_addressing) eqn:EVAL in LOAD.
    * specialize (LOAD v). econstructor; split.
      assert (eval_addressing tge sp addr rs' ## args = Some v).
      { rewrite <- EVAL.
        rewrite (same_rs_subst rs rs' args SAME).
        apply eval_addressing_preserved. exact symbols_preserved.
      }
      eapply exec_Iload; eauto. eapply has_loaded_default; eauto.
      intros a EVAL'; rewrite H0 in EVAL'; inv EVAL'. apply LOAD; auto.
      constructor; auto using same_rs_write. 
    * econstructor; split.
      assert (eval_addressing tge sp addr rs' ## args = None).
      { rewrite <- EVAL.
        rewrite (same_rs_subst rs rs' args SAME).
        apply eval_addressing_preserved. exact symbols_preserved.
      }
      eapply exec_Iload; eauto. eapply has_loaded_default; eauto.
      intros a EVAL'; rewrite H0 in EVAL'; inv EVAL'.
      constructor; auto using same_rs_write.
- (* store *)
  econstructor; split.
  assert (eval_addressing tge sp addr rs' ## args = Some a).
  { rewrite <- H0.
    rewrite (same_rs_subst rs rs' args SAME).
    apply eval_addressing_preserved. exact symbols_preserved.
  }
  rewrite (same_rs_read rs rs' src SAME) in H1.
  eapply exec_Istore; eauto.
  constructor; auto.
(* call *)
- econstructor; split.
  eapply exec_Icall with (fd := transf_fundef fd); eauto.
  eapply find_function_translated; eauto.
  { rewrite <- (same_find_function ge rs rs') by assumption.
    assumption. }
  apply sig_preserved.
  rewrite (same_rs_subst rs rs' args SAME).  
  constructor. constructor; auto. constructor; auto.
(* tailcall *)
- econstructor; split.
  eapply exec_Itailcall with (fd := transf_fundef fd); eauto.
    eapply find_function_translated; eauto.
  { rewrite <- (same_find_function ge rs rs') by assumption.
    assumption. }
    apply sig_preserved.
  rewrite (same_rs_subst rs rs' args SAME).  
  constructor. auto.
(* builtin *)
- econstructor; split.
  eapply exec_Ibuiltin; eauto.
  eapply eval_builtin_args_preserved with (ge1 := ge); eauto. exact symbols_preserved.
  {
    replace (fun r : positive => rs' # r) with (fun r : positive => rs # r).
    eassumption.
    apply functional_extensionality.
    auto using same_rs_read.
  }
  eapply external_call_symbols_preserved; eauto. apply senv_preserved.
  constructor; auto.
  auto using same_rs_setres.
(* cond *)
- econstructor; split.
  eapply exec_Icond; eauto.
  rewrite <- (same_rs_subst rs rs' args SAME); eassumption.
  constructor; auto.
(* jumptbl *)
- econstructor; split.
  eapply exec_Ijumptable; eauto.
  rewrite <- (same_rs_read rs rs' arg SAME); eassumption.
  constructor; auto.
(* return *)
- econstructor; split.
  eapply exec_Ireturn; eauto.
  destruct or; cbn.
  + rewrite <- (same_rs_read rs rs' r SAME) by auto.
    constructor; auto.
  + constructor; auto.
(* internal function *)
-  simpl. econstructor; split.
  eapply exec_function_internal; eauto.
  constructor; auto.
  cbn.
  apply same_rs_refl.
(* external function *)
- econstructor; split.
  eapply exec_function_external; eauto.
    eapply external_call_symbols_preserved; eauto. apply senv_preserved.
  constructor; auto.
(* return *)
- inv STACKS. inv H1.
  econstructor; split.
  eapply exec_return; eauto.
  constructor; auto using same_rs_write.
Qed.

Lemma transf_initial_states:
  forall S1, RTL.initial_state prog S1 ->
  exists S2, RTL.initial_state tprog S2 /\ match_states S1 S2.
Proof.
  intros. inv H. econstructor; split.
  econstructor.
    eapply (Genv.init_mem_transf TRANSL); eauto.
    rewrite symbols_preserved. rewrite (match_program_main TRANSL). eauto.
    eapply function_ptr_translated; eauto.
    rewrite <- H3; apply sig_preserved.
  constructor. constructor.
Qed.

Lemma transf_final_states:
  forall S1 S2 r, match_states S1 S2 -> RTL.final_state S1 r -> RTL.final_state S2 r.
Proof.
  intros. inv H0. inv H. inv STACKS. constructor.
Qed.

Theorem transf_program_correct:
  forward_simulation (RTL.semantics prog) (RTL.semantics tprog).
Proof.
  eapply forward_simulation_step.
  apply senv_preserved.
  eexact transf_initial_states.
  eexact transf_final_states.
  exact step_simulation.
Qed.

End PRESERVATION.