Lazy loading of opaque proofs: fast as -dont-load-proofs without its drawbacks

 The recent experiment with -dont-load-proofs in the stdlib showed that
 this options isn't fully safe: some axioms were generated (Include ?
 functor application ? This is still to be fully understood).

 Instead, I've implemented an idea of Yann: only load opaque proofs when
 we need them. This is almost as fast as -dont-load-proofs (on the stdlib,
 we're now 15% faster than before instead of 20% faster with -dont-load-proofs),
 but fully compatible with Coq standard behavior.

 Technically, the const_body field of Declarations.constant_body now regroup
 const_body + const_opaque + const_inline in a ternary type. It is now either:
  - Undef : an axiom or parameter, with an inline info
  - Def : a transparent definition, with a constr_substituted
  - OpaqueDef : an opaque definition, with a lazy constr_substitued
 Accessing the lazy constr of an OpaqueDef might trigger the read on disk of
 the final section of a .vo, where opaque proofs are located.

 Some functions (body_of_constant, is_opaque, constant_has_body) emulate
 the behavior of the old fields. The rest of Coq (including the checker)
 has been adapted accordingly, either via direct access to the new const_body
 or via these new functions. Many places look nicer now (ok, subjective notion).

 There are now three options: -lazy-load-proofs (default), -force-load-proofs
 (earlier semantics), -dont-load-proofs. Note that -outputstate now implies
 -force-load-proofs (otherwise the marshaling fails on some delayed lazy).

 On the way, I fixed what looked like a bug : a module type
 (T with Definition x := c) was accepted even when x in T was opaque.
 I also tried to clarify Subtyping.check_constant.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@13952 85f007b7-540e-0410-9357-904b9bb8a0f7

3 files changed, 25 insertions, 8 deletions

diff --git a/library/impargs.ml b/library/impargs.ml
index fad81b1529..3f60bf96aa 100644
--- a/library/impargs.ml
+++ b/library/impargs.ml
@@ -157,7 +157,7 @@ let is_flexible_reference env bound depth f =
     | Rel n -> (* since local definitions have been expanded *) false
     | Const kn ->
         let cb = Environ.lookup_constant kn env in
-        cb.const_body <> None & not cb.const_opaque
+	(match cb.const_body with Def _ -> true | _ -> false)
     | Var id ->
         let (_,value,_) = Environ.lookup_named id env in value <> None
     | Ind _ | Construct _ -> false
diff --git a/library/library.ml b/library/library.ml
index 3d72c5fdb1..447d536107 100644
--- a/library/library.ml
+++ b/library/library.ml
@@ -382,25 +382,39 @@ let try_locate_qualified_library (loc,qid) =
 (************************************************************************)
 (* Internalise libraries *)
 
-let mk_library md get_table digest = 
-  let md_compiled = 
-    LightenLibrary.load ~load_proof:!Flags.load_proofs get_table md.md_compiled
+let mk_library md table digest =
+  let md_compiled =
+    LightenLibrary.load ~load_proof:!Flags.load_proofs table md.md_compiled
   in {
     library_name     = md.md_name;
     library_compiled = md_compiled;
     library_objects  = md.md_objects;
     library_deps     = md.md_deps;
     library_imports  = md.md_imports;
-    library_digest    = digest 
+    library_digest    = digest
   }
 
+let fetch_opaque_table (f,pos,digest) =
+  try
+    let ch = System.with_magic_number_check raw_intern_library f in
+    seek_in ch pos;
+    if System.marshal_in ch <> digest then failwith "File changed!";
+    let table = (System.marshal_in ch : LightenLibrary.table) in
+    close_in ch;
+    table
+  with _ ->
+    error
+      ("The file "^f^" is inaccessible or has changed,\n" ^
+       "cannot load some opaque constant bodies in it.\n")
+
 let intern_from_file f =
   let ch = System.with_magic_number_check raw_intern_library f in
   let lmd = System.marshal_in ch in
+  let pos = pos_in ch in
   let digest = System.marshal_in ch in
-  let get_table () = (System.marshal_in ch : LightenLibrary.table) in
+  let table = lazy (fetch_opaque_table (f,pos,digest)) in
   register_library_filename lmd.md_name f;
-  let library = mk_library lmd get_table digest in
+  let library = mk_library lmd table digest in
   close_in ch;
   library
 
diff --git a/library/states.ml b/library/states.ml
index 4619b3b537..c88858f7ed 100644
--- a/library/states.ml
+++ b/library/states.ml
@@ -20,7 +20,10 @@ let unfreeze (fl,fs) =
 let (extern_state,intern_state) =
   let (raw_extern, raw_intern) =
     extern_intern Coq_config.state_magic_number ".coq" in
-  (fun s -> raw_extern s (freeze())),
+  (fun s ->
+    if !Flags.load_proofs <> Flags.Force then
+      Util.error "Write State only works with option -force-load-proofs";
+    raw_extern s (freeze())),
   (fun s ->
     unfreeze
       (with_magic_number_check (raw_intern (Library.get_load_paths ())) s);