New parser based on new version of the Coq backend of Menhir (#276)

What's new:

1. A rewrite of the Coq interpreter of Menhir automaton, with
   dependent types removing the need for runtime checks for the
   well-formedness of the LR stack. This seem to cause some speedup on
   the parsing time (~10% for lexing + parsing).

2. Thanks to 1., it is now possible to avoid the use of int31 for
   comparing symbols: Since this is only used for validation,
   positives are enough.

3. Speedup of Validation: on my machine, the time needed for compiling
   Parser.v goes from about 2 minutes to about 1 minute. This seem to
   be related to a performance bug in the completeness validator and
   to the use of positive instead of int31.

3. Menhir now generates a dedicated inductive type for
   (semantic-value-carrying) tokens (in addition to the already
   existing inductive type for (non-semantic-value-carrying)
   terminals. The end result is that the OCaml support code for the
   parser no longer contain calls to Obj.magic. The bad side of this
   change is that the formal specification of the parser is perhaps
   harder to read.

4. The parser and its library are now free of axioms (I used to use
   axiom K and proof irrelevance for easing proofs involving dependent
   types).

5. Use of a dedicated custom negative coinductive type for the input
   stream of tokens, instead of Coq stdlib's `Stream`. `Stream` is a
   positive coinductive type, which are now deprecated by Coq.

6. The fuel of the parser is now specified using its logarithm instead
   of its actual value. This makes it possible to give large fuel
   values instead of using the `let rec fuel = S fuel` hack.

7. Some refactoring in the lexer, the parser and the Cabs syntax tree.

The corresponding changes in Menhir have been released as part of
version 20190626. The `MenhirLib` directory is identical to the
content of the `src` directory of the corresponding `coq-menhirlib`
opam package except that:
   - In order to try to make CompCert compatible with several Menhir
     versions without updates, we do not check the version of menhir
     is compatible with the version of coq-menhirlib. Hence the
     `Version.v` file is not present in CompCert's copy.
   - Build-system related files have been removed.

1 files changed, 247 insertions, 0 deletions

diff --git a/MenhirLib/Alphabet.v b/MenhirLib/Alphabet.v
new file mode 100644
index 00000000..29070e3d
--- /dev/null
+++ b/MenhirLib/Alphabet.v
@@ -0,0 +1,247 @@
+(****************************************************************************)
+(*                                                                          *)
+(*                                   Menhir                                 *)
+(*                                                                          *)
+(*           Jacques-Henri Jourdan, CNRS, LRI, Université Paris Sud         *)
+(*                                                                          *)
+(*  Copyright Inria. All rights reserved. This file is distributed under    *)
+(*  the terms of the GNU Lesser General Public License as published by the  *)
+(*  Free Software Foundation, either version 3 of the License, or (at your  *)
+(*  option) any later version, as described in the file LICENSE.            *)
+(*                                                                          *)
+(****************************************************************************)
+
+From Coq Require Import Omega List Syntax Relations RelationClasses.
+
+Local Obligation Tactic := intros.
+
+(** A comparable type is equiped with a [compare] function, that define an order
+   relation. **)
+Class Comparable (A:Type) := {
+  compare : A -> A -> comparison;
+  compare_antisym : forall x y, CompOpp (compare x y) = compare y x;
+  compare_trans :  forall x y z c,
+    (compare x y) = c -> (compare y z) = c -> (compare x z) = c
+}.
+
+Theorem compare_refl {A:Type} (C: Comparable A) :
+  forall x, compare x x = Eq.
+Proof.
+intros.
+pose proof (compare_antisym x x).
+destruct (compare x x); intuition; try discriminate.
+Qed.
+
+(** The corresponding order is a strict order. **)
+Definition comparableLt {A:Type} (C: Comparable A) : relation A :=
+  fun x y => compare x y = Lt.
+
+Instance ComparableLtStrictOrder {A:Type} (C: Comparable A) :
+  StrictOrder (comparableLt C).
+Proof.
+apply Build_StrictOrder.
+unfold Irreflexive, Reflexive, complement, comparableLt.
+intros.
+pose proof H.
+rewrite <- compare_antisym in H.
+rewrite H0 in H.
+discriminate H.
+unfold Transitive, comparableLt.
+intros x y z.
+apply compare_trans.
+Qed.
+
+(** nat is comparable. **)
+Program Instance natComparable : Comparable nat :=
+  { compare := Nat.compare }.
+Next Obligation.
+symmetry.
+destruct (Nat.compare x y)  as [] eqn:?.
+rewrite Nat.compare_eq_iff in Heqc.
+destruct Heqc.
+rewrite Nat.compare_eq_iff.
+trivial.
+rewrite <- nat_compare_lt in *.
+rewrite <- nat_compare_gt in *.
+trivial.
+rewrite <- nat_compare_lt in *.
+rewrite <- nat_compare_gt in *.
+trivial.
+Qed.
+Next Obligation.
+destruct c.
+rewrite Nat.compare_eq_iff in *; destruct H; assumption.
+rewrite <- nat_compare_lt in *.
+apply (Nat.lt_trans _ _ _ H H0).
+rewrite <- nat_compare_gt in *.
+apply (gt_trans _ _ _ H H0).
+Qed.
+
+(** A pair of comparable is comparable. **)
+Program Instance PairComparable {A:Type} (CA:Comparable A) {B:Type} (CB:Comparable B) :
+  Comparable (A*B) :=
+  { compare := fun x y =>
+      let (xa, xb) := x in let (ya, yb) := y in
+      match compare xa ya return comparison with
+        | Eq => compare xb yb
+        | x => x
+      end }.
+Next Obligation.
+destruct x, y.
+rewrite <- (compare_antisym a a0).
+rewrite <- (compare_antisym b b0).
+destruct (compare a a0); intuition.
+Qed.
+Next Obligation.
+destruct x, y, z.
+destruct (compare a a0) as [] eqn:?, (compare a0 a1) as [] eqn:?;
+try (rewrite <- H0 in H; discriminate);
+try (destruct (compare a a1) as [] eqn:?;
+  try (rewrite <- compare_antisym in Heqc0;
+         rewrite CompOpp_iff in Heqc0;
+         rewrite (compare_trans _ _ _  _ Heqc0 Heqc2) in Heqc1;
+         discriminate);
+  try (rewrite <- compare_antisym in Heqc1;
+         rewrite CompOpp_iff in Heqc1;
+         rewrite (compare_trans _ _ _ _ Heqc2 Heqc1) in Heqc0;
+         discriminate);
+  assumption);
+rewrite (compare_trans _ _ _ _ Heqc0 Heqc1);
+try assumption.
+apply (compare_trans _ _ _ _ H H0).
+Qed.
+
+(** Special case of comparable, where equality is Leibniz equality. **)
+Class ComparableLeibnizEq {A:Type} (C: Comparable A) :=
+  compare_eq : forall x y, compare x y = Eq -> x = y.
+
+(** Boolean equality for a [Comparable]. **)
+Definition compare_eqb {A:Type} {C:Comparable A} (x y:A) :=
+  match compare x y with
+    | Eq => true
+    | _ => false
+  end.
+
+Theorem compare_eqb_iff {A:Type} {C:Comparable A} {U:ComparableLeibnizEq C} :
+  forall x y, compare_eqb x y = true <-> x = y.
+Proof.
+unfold compare_eqb.
+intuition.
+apply compare_eq.
+destruct (compare x y); intuition; discriminate.
+destruct H.
+rewrite compare_refl; intuition.
+Qed.
+
+Instance NComparableLeibnizEq : ComparableLeibnizEq natComparable := Nat.compare_eq.
+
+(** A pair of ComparableLeibnizEq is ComparableLeibnizEq **)
+Instance PairComparableLeibnizEq
+  {A:Type} {CA:Comparable A} (UA:ComparableLeibnizEq CA)
+  {B:Type} {CB:Comparable B} (UB:ComparableLeibnizEq CB) :
+    ComparableLeibnizEq (PairComparable CA CB).
+Proof.
+intros x y; destruct x, y; simpl.
+pose proof (compare_eq a a0); pose proof (compare_eq b b0).
+destruct (compare a a0); try discriminate.
+intuition.
+destruct H2, H0.
+reflexivity.
+Qed.
+
+(** An [Finite] type is a type with the list of all elements. **)
+Class Finite (A:Type) := {
+  all_list : list A;
+  all_list_forall : forall x:A, In x all_list
+}.
+
+(** An alphabet is both [ComparableLeibnizEq] and [Finite]. **)
+Class Alphabet (A:Type) := {
+  AlphabetComparable :> Comparable A;
+  AlphabetComparableLeibnizEq :> ComparableLeibnizEq AlphabetComparable;
+  AlphabetFinite :> Finite A
+}.
+
+(** The [Numbered] class provides a conveniant way to build [Alphabet] instances,
+   with a good computationnal complexity. It is mainly a injection from it to
+   [positive] **)
+Class Numbered (A:Type) := {
+  inj : A -> positive;
+  surj : positive -> A;
+  surj_inj_compat : forall x, surj (inj x) = x;
+  inj_bound : positive;
+  inj_bound_spec : forall x, (inj x < Pos.succ inj_bound)%positive
+}.
+
+Program Instance NumberedAlphabet {A:Type} (N:Numbered A) : Alphabet A :=
+  { AlphabetComparable := {| compare := fun x y => Pos.compare (inj x) (inj y) |};
+    AlphabetFinite :=
+      {| all_list := fst (Pos.iter
+                           (fun '(l, p) => (surj p::l, Pos.succ p))
+                           ([], 1%positive) inj_bound) |} }.
+Next Obligation. simpl. now rewrite <- Pos.compare_antisym. Qed.
+Next Obligation.
+  match goal with c : comparison |- _ => destruct c end.
+  - rewrite Pos.compare_eq_iff in *. congruence.
+  - rewrite Pos.compare_lt_iff in *. eauto using Pos.lt_trans.
+  - rewrite Pos.compare_gt_iff in *. eauto using Pos.lt_trans.
+Qed.
+Next Obligation.
+  intros x y. unfold compare. intros Hxy.
+  assert (Hxy' : inj x = inj y).
+  (* We do not use [Pos.compare_eq_iff] directly to make sure the
+     proof is executable. *)
+  { destruct (Pos.eq_dec (inj x) (inj y)) as [|[]]; [now auto|].
+    now apply Pos.compare_eq_iff. }
+  (* Using rewrite here leads to non-executable proofs. *)
+  transitivity (surj (inj x)).
+  { apply eq_sym, surj_inj_compat. }
+  transitivity (surj (inj y)); cycle 1.
+  { apply surj_inj_compat. }
+  apply f_equal, Hxy'.
+Defined.
+Next Obligation.
+  rewrite <-(surj_inj_compat x).
+  generalize (inj_bound_spec x). generalize (inj x). clear x. intros x.
+  match goal with |- ?Hx -> In ?s (fst ?p) =>
+    assert ((Hx -> In s (fst p)) /\ snd p = Pos.succ inj_bound); [|now intuition] end.
+  rewrite Pos.lt_succ_r.
+  induction inj_bound as [|y [IH1 IH2]] using Pos.peano_ind;
+    (split; [intros Hx|]); simpl.
+  - rewrite (Pos.le_antisym _ _ Hx); auto using Pos.le_1_l.
+  - auto.
+  - rewrite Pos.iter_succ. destruct Pos.iter; simpl in *. subst.
+    rewrite Pos.le_lteq in Hx. destruct Hx as [?%Pos.lt_succ_r| ->]; now auto.
+  - rewrite Pos.iter_succ. destruct Pos.iter. simpl in IH2. subst. reflexivity.
+Qed.
+
+(** Definitions of [FSet]/[FMap] from [Comparable] **)
+Require Import OrderedTypeAlt.
+Require FSetAVL.
+Require FMapAVL.
+Import OrderedType.
+
+Module Type ComparableM.
+  Parameter t : Type.
+  Declare Instance tComparable : Comparable t.
+End ComparableM.
+
+Module OrderedTypeAlt_from_ComparableM (C:ComparableM) <: OrderedTypeAlt.
+  Definition t := C.t.
+  Definition compare : t -> t -> comparison := compare.
+
+  Infix "?=" := compare (at level 70, no associativity).
+
+  Lemma compare_sym x y : (y?=x) = CompOpp (x?=y).
+  Proof. exact (Logic.eq_sym (compare_antisym x y)). Qed.
+  Lemma compare_trans c x y z :
+    (x?=y) = c -> (y?=z) = c -> (x?=z) = c.
+  Proof.
+  apply compare_trans.
+  Qed.
+End OrderedTypeAlt_from_ComparableM.
+
+Module OrderedType_from_ComparableM (C:ComparableM) <: OrderedType.
+  Module Alt := OrderedTypeAlt_from_ComparableM C.
+  Include (OrderedType_from_Alt Alt).
+End OrderedType_from_ComparableM.