(** Neededness analysis for ARM operators *)

Definition needs_of_condition (cond: condition): list nval := nil.Definition needs_of_shift (s: shift) (nv: nval): nval :=
  match s with
  | Slsl x => shlimm nv x
  | Slsr x => shruimm nv x
  | Sasr x => shrimm nv x
  | Sror x => ror nv x
  end.Definition op1 (nv: nval) := nv :: nil.Definition op2 (nv: nval) := nv :: nv :: nil.Definition op2shift (s: shift) (nv: nval) := nv :: needs_of_shift s nv :: nil.Definition needs_of_operation (op: operation) (nv: nval): list nval :=
  match op with
  | Omove => nv::nil
  | Ointconst n => nil
  | Ofloatconst n => nil
  | Osingleconst n => nil
  | Oaddrsymbol id ofs => nil
  | Oaddrstack ofs => nil
  | Ocast8signed => op1 (sign_ext 8 nv)
  | Ocast16signed => op1 (sign_ext 16 nv)
  | Oadd => op2 (modarith nv)
  | Oaddshift s => op2shift s (modarith nv)
  | Oaddimm _ => op1 (modarith nv)
  | Osub => op2 (default nv)
  | Osubshift s => op2shift s (default nv)
  | Orsubshift s => op2shift s (default nv)
  | Orsubimm _ => op1 (default nv)
  | Omul => op2 (modarith nv)
  | Omla => let n := modarith nv in let n2 := modarith n in n2::n2::n::nil
  | Omulhu | Omulhs | Odiv | Odivu => let n := default nv in n::n::nil
  | Oand => op2 (bitwise nv)
  | Oandshift s => op2shift s (bitwise nv)
  | Oandimm n => op1 (andimm nv n)
  | Oor => op2 (bitwise nv)
  | Oorshift s => op2shift s (bitwise nv)
  | Oorimm n => op1 (orimm nv n)
  | Oxor => op2 (bitwise nv)
  | Oxorshift s => op2shift s (bitwise nv)
  | Oxorimm n => op1 (bitwise nv)
  | Obic => let n := bitwise nv in n::bitwise n::nil
  | Obicshift s => let n := bitwise nv in n::needs_of_shift s (bitwise n)::nil
  | Onot => op1 (bitwise nv)
  | Onotshift s => op1 (needs_of_shift s (bitwise nv))
  | Oshl | Oshr | Oshru => op2 (default nv)
  | Oshift s => op1 (needs_of_shift s nv)
  | Oshrximm _ => op1 (default nv)
  | Onegf | Oabsf => op1 (default nv)
  | Oaddf | Osubf | Omulf | Odivf => op2 (default nv)
  | Onegfs | Oabsfs => op1 (default nv)
  | Oaddfs | Osubfs | Omulfs | Odivfs => op2 (default nv)
  | Ofloatofsingle | Osingleoffloat => op1 (default nv)
  | Ointoffloat | Ointuoffloat | Ofloatofint | Ofloatofintu => op1 (default nv)
  | Ointofsingle | Ointuofsingle | Osingleofint | Osingleofintu => op1 (default nv)
  | Omakelong => op2 (default nv)
  | Olowlong | Ohighlong => op1 (default nv)
  | Ocmp c => needs_of_condition c
  end.Definition operation_is_redundant (op: operation) (nv: nval): bool :=
  match op with
  | Ocast8signed => sign_ext_redundant 8 nv
  | Ocast16signed => sign_ext_redundant 16 nv
  | Oandimm n => andimm_redundant nv n
  | Oorimm n => orimm_redundant nv n
  | _ => false
  end.Ltac InvAgree :=
  match goal with
  | [H: vagree_list nil _ _ |- _ ] => inv H; InvAgree
  | [H: vagree_list (_::_) _ _ |- _ ] => inv H; InvAgree
  | _ => idtac
  end.Ltac TrivialExists :=
  match goal with
  | [ |- exists v, Some ?x = Some v /\ _ ] => exists x; split; auto
  | _ => idtac
  end.

Lemma needs_of_operation_sound: forall op args v nv args', eval_operation ge (Vptr sp Ptrofs.zero) op args m = Some v -> vagree_list args args' (needs_of_operation op nv) -> nv <> Nothing -> exists v', eval_operation ge (Vptr sp Ptrofs.zero) op args' m' = Some v' /\ vagree v v' nv.