Attach _Alignas to names and refactor _Alignas checks (#133)

* Refactor common code of alignas.

Instead of working on attributes the function now works directly
on the type since the check always performed an extraction of
attributes from a type. 
Bug 23393

* Attach _Alignas to the name.

Bug 23393

* Attach "aligned" attributes to names

So that __attribute((aligned(N))) remains consistent with _Alignas(N).
gcc and clang apply "aligned" attributes to names, with a special case
for typedefs:
    typedef __attribute((aligned(16))) int int_al_16;
    int_al_16 * p;
    __attribute((aligned(16))) int * q;

For gcc, p is naturally-aligned pointer to 16-aligned int and
q is 16-aligned pointer to naturally-aligned int.

For CompCert with this commit, both p and q are 16-aligned pointers
to naturally-aligned int.

* Resurrect the alignment test involving typedef

The test was removed because it involved an _Alignas in a typedef,
which is no longer supported.  However the same effect can be achieved
with an "aligned" attribute, which is still supported in typedef.

6 files changed, 22 insertions, 20 deletions

diff --git a/cfrontend/C2C.ml b/cfrontend/C2C.ml
index ecaffbc6..1bbcb146 100644
--- a/cfrontend/C2C.ml
+++ b/cfrontend/C2C.ml
@@ -307,14 +307,14 @@ let builtins =
 (** ** The known attributes *)
 
 let attributes = [
-  (* type-related *)
-  ("aligned", Cutil.Attr_type);
+  (* type-related -- currently none *)
   (* struct-related *)
   ("packed", Cutil.Attr_struct);
   (* function-related *)
   ("noreturn", Cutil.Attr_function);
   ("noinline",Cutil.Attr_function);
   (* name-related *)
+  ("aligned", Cutil.Attr_name);
   ("section", Cutil.Attr_name);
   ("unused", Cutil.Attr_name)
 ]
diff --git a/cparser/Cutil.ml b/cparser/Cutil.ml
index a0a2cf56..ea9713d5 100644
--- a/cparser/Cutil.ml
+++ b/cparser/Cutil.ml
@@ -110,7 +110,8 @@ let declare_attributes l =
   List.iter (fun (n,c) -> declare_attribute n c) l
 
 let class_of_attribute = function
-  | AConst | AVolatile | ARestrict | AAlignas _ -> Attr_type
+  | AConst | AVolatile | ARestrict -> Attr_type
+  | AAlignas _ -> Attr_name
   | Attr(name, args) ->
       try Hashtbl.find attr_class (normalize_attrname name)
       with Not_found -> Attr_unknown
@@ -258,8 +259,8 @@ let strip_last_attribute typ  =
     l,TEnum(n,r)
 
 (* Check whether the attributes contain _Alignas attribute *)
-let has_std_alignas attr =
-  List.exists (function | AAlignas _ -> true | _ -> false) attr
+let has_std_alignas env typ  =
+  List.exists (function | AAlignas _ -> true | _ -> false) (attributes_of_type env typ)
 
 (* Extracting alignment value from a set of attributes.  Return 0 if none. *)
 
diff --git a/cparser/Cutil.mli b/cparser/Cutil.mli
index 3f8d8dcd..dc9dc0cc 100644
--- a/cparser/Cutil.mli
+++ b/cparser/Cutil.mli
@@ -58,8 +58,8 @@ val erase_attributes_type : Env.t -> typ -> typ
   (* Erase the attributes of the given type. *)
 val change_attributes_type : Env.t -> (attributes -> attributes) -> typ -> typ
   (* Apply the given function to the top-level attributes of the given type *)
-val has_std_alignas : attributes -> bool
-  (* Do the attributes contain the C11 _Alignas attribute *)
+val has_std_alignas :  Env.t -> typ -> bool
+  (* Do the attributes of the type contain the C11 _Alignas attribute *)
 
 type attribute_class =
   | Attr_name           (* Attribute applies to the names being declared  *)
diff --git a/cparser/Elab.ml b/cparser/Elab.ml
index 146cab2e..27569ff5 100644
--- a/cparser/Elab.ml
+++ b/cparser/Elab.ml
@@ -871,7 +871,7 @@ and elab_parameter env (PARAM (spec, id, decl, attr, loc)) =
   let ty1 = argument_conversion env1 ty in
   if is_qualified_array ty1 then
     error loc "type qualifier used in non-outermost array type derivation";
-  if has_std_alignas (attributes_of_type env ty) then begin
+  if has_std_alignas env ty then begin
     if id <> "" then
       error loc "alignment specified for parameter '%s'" id
     else
@@ -928,15 +928,18 @@ and elab_init_name_group loc env (spec, namelist) =
     let ((ty, _), env1) =
       elab_type_declarator loc env bty decl in
     let a = elab_attributes env attr in
-    if inl && not (is_function_type env ty) then
+    let has_fun_typ = is_function_type env ty in
+    if inl && not has_fun_typ then
       error loc "'inline' can only appear on functions";
     let a' =
       if noret then begin
         warning loc Celeven_extension "_Noreturn functions are a C11 extension";
-        if not (is_function_type env ty) then
+        if not has_fun_typ then
           error loc "'_Noreturn' can only appear on functions";
         add_attributes [Attr("noreturn",[])] a
       end else a in
+    if has_std_alignas env ty && has_fun_typ then
+      error loc "alignment specified for function '%s'" id;
     ((id, add_attributes_type a' ty, init), env1) in
   (mmap elab_one_name env' namelist, sto, tydef)
 
@@ -973,7 +976,7 @@ and elab_field_group env (Field_group (spec, fieldlist, loc)) =
             error loc
               "the type of bit-field '%a' must be an integer type no bigger than 'int'" pp_field id;
             None,env
-          end else if has_std_alignas (attributes_of_type env' ty) then begin
+          end else if has_std_alignas env' ty then begin
             error loc "alignment specified for bit-field '%a'" pp_field id;
             None, env
           end else begin
@@ -2354,7 +2357,7 @@ let enter_typedefs loc env sto dl =
   List.fold_left (fun env (s, ty, init) ->
     if init <> NO_INIT then
       error loc "initializer in typedef";
-    if has_std_alignas (attributes_of_type env ty) then
+    if has_std_alignas env ty then
       error loc "alignment specified for typedef '%s'" s;
     match previous_def Env.lookup_typedef env s with
     | Some (s',ty') when Env.in_current_scope env s' ->
@@ -2383,7 +2386,7 @@ let enter_decdefs local nonstatic_inline loc env sto dl =
     warning loc Missing_declarations "declaration does not declare anything";
   let enter_decdef (decls, env) (s, ty, init) =
     let isfun = is_function_type env ty in
-    if sto = Storage_register && has_std_alignas (attributes_of_type env ty) then
+    if sto = Storage_register && has_std_alignas env ty then
       error loc "alignment specified for 'register' object '%s'" s;
     if sto = Storage_extern && init <> NO_INIT then
       error loc "'extern' declaration variable has an initializer";
@@ -2599,7 +2602,7 @@ let elab_fundef genv spec name defs body loc =
   let (ty_ret, params, vararg, attr) =
     match ty with
     | TFun(ty_ret, Some params, vararg, attr) ->
-         if has_std_alignas (attr @ (attributes_of_type genv ty_ret)) then
+         if has_std_alignas genv ty then
            error loc "alignment specified for function '%s'" s;
          if wrap incomplete_type loc genv ty_ret && not (is_void_type genv ty_ret) then
            fatal_error loc "incomplete result type %a in function definition"
diff --git a/test/regression/Results/alignas b/test/regression/Results/alignas
index 9372096a..620b5e76 100644
--- a/test/regression/Results/alignas
+++ b/test/regression/Results/alignas
@@ -1,6 +1,7 @@
 a: size = 4, address mod 16 = 0
 b: size = 12, address mod 16 = 0
 bb: size = 12, address mod 16 = 0
+bbb: size = 12, address mod 16 = 0
 c: size = 32, address mod 16 = 0
 d: size = 32, address mod 64 = 0
 e: size = 16, address mod 16 = 0
diff --git a/test/regression/alignas.c b/test/regression/alignas.c
index 23966b59..777c13a5 100644
--- a/test/regression/alignas.c
+++ b/test/regression/alignas.c
@@ -7,7 +7,7 @@
 #endif
 
 #if  __STDC_VERSION__ < 201100 && defined(__GNUC__)
-#define _Alignas(x) __attribute__((aligned(x)))
+#define _Alignas(x) __attribute((aligned(x)))
 #endif
 
 /* Base type */
@@ -20,10 +20,9 @@ _Alignas(16) int b[3];
 typedef int int3[3];
 _Alignas(16) int3 bb;
 
-#if 0
-typedef _Alignas(16) int int16;
+/* _Alignas is not allowed in typedefs but the "aligned" attribute is */
+typedef __attribute((aligned(16))) int int16;
 int16 bbb[3];
-#endif
 
 char filler2;
 
@@ -74,10 +73,8 @@ int main()
          (unsigned) sizeof(b), ((unsigned) &b) & 0xF);
   printf("bb: size = %u, address mod 16 = %u\n",
          (unsigned) sizeof(bb), ((unsigned) &bb) & 0xF);
-#if 0
   printf("bbb: size = %u, address mod 16 = %u\n",
          (unsigned) sizeof(bbb), ((unsigned) &bbb) & 0xF);
-#endif
   printf("c: size = %u, address mod 16 = %u\n",
          (unsigned) sizeof(c), ((unsigned) &c) & 0xF);
   printf("d: size = %u, address mod 64 = %u\n",