ada: Split Library_Unit using multiple wrappers

The Library_Unit field was used for all sorts of different purposes,
which led to confusing code.

This patch splits Library_Unit into much more specific wrapper
subprograms that should be called instead of [Set_]Library_Unit.
Predicates and pragmas Assert are used to catch misuses of these.
We document the semantics, especially "surprising" cases (e.g.
internally-generated with clauses can refer to package bodies).

This change does not fix gigi, codepeer, spark, or llvm
to use the new wrappers; so far, they are used only in
the GNAT front end.

gcc/ada/ChangeLog:

	* sinfo.ads (Library_Unit): Rewrite documentation. Note that
	the "??? not (always) true..." comment was not true;
	the Subunit_Parent never points to the spec.
	(N_Compilation_Unit): Improve documentation. The Aux_ node
	was not created to solve the mentioned problems; it was
	created because the size of nodes was limited.
	Misc doc improvements.
	* sinfo-utils.ads: Add new wrappers for Library_Unit field.
	Use subtypes with predicates for the parameters.
	(First_Real_Statement): Still used in codepeer.
	* sinfo-utils.adb: Add new wrappers for Library_Unit field,
	with suitable assertions.
	* sem_prag.adb: Use new field wrapper names.
	(Matching_Name): New name for Same_Name to avoid
	potential confusion with the other function with the
	same name (Sem_Util.Same_Name), which is also called
	in this same file.
	(Matching_Convention): Change Same_Convention to match
	Matching_Name.
	* sem_util.ads (Same_Name): Improve comments; the old comment
	implied that it works for all names, which was not true.
	* sem_util.adb: Use new field wrapper names.
	* gen_il-gen.adb: Rename N_Unit_Body to be N_Lib_Unit_Body.
	Plain "unit" is ambiguous in Ada (library unit, compilation
	unit, program unit, etc).
	Add new union types N_Lib_Unit_Declaration and
	N_Lib_Unit_Renaming_Declaration.
	* gen_il-gen-gen_nodes.adb (Compute_Ranges): Raise exception
	earlier (it is already raised later, in Verify_Type_Table).
	Add a comment explaining why it might be raised.
	* gen_il-types.ads: Rename N_Unit_Body to be N_Lib_Unit_Body, and add
	new N_Lib_Unit_Declaration and N_Lib_Unit_Renaming_Declaration.
	* einfo.ads: Fix obsolete comment (was left over from before
	the "variable-sized nodes").
	* exp_ch7.adb: Use new field wrapper names.
	* exp_disp.adb: Use new field wrapper names.
	* exp_unst.adb: Use new field wrapper names.
	* exp_util.adb: Use new field wrapper names.
	* fe.h: Add new field wrapper names. These are currently not
	used in gigi, but this change prepares for using them in
	gigi.
	* inline.adb: Use new field wrapper names.
	* lib.adb: Use new field wrapper names.
	Comment improvements.
	* lib-load.adb: Use new field wrapper names.
	Minor cleanup.
	* lib-writ.adb: Use new field wrapper names.
	* live.adb: Use new field wrapper names.
	* par-load.adb: Use new field wrapper names.
	Comment improvements. Minor cleanup.
	* rtsfind.adb: Use new field wrapper names.
	* sem.adb: Use new field wrapper names.
	* sem_ch10.adb: Use new field wrapper names.
	Comment improvements. Minor cleanup.
	* sem_ch12.adb: Use new field wrapper names.
	* sem_ch7.adb: Use new field wrapper names.
	* sem_ch8.adb: Use new field wrapper names.
	* sem_elab.adb: Use new field wrapper names.
	Comment improvements.
	* errout.adb (Output_Source_Line): Fix blowup in some
	obscure cases, where List_Pragmas is not fully set up.

1 files changed, 61 insertions, 2 deletions

diff --git a/gcc/ada/sinfo-utils.ads b/gcc/ada/sinfo-utils.ads
index 9acb620..ebb9699 100644
--- a/gcc/ada/sinfo-utils.ads
+++ b/gcc/ada/sinfo-utils.ads
@@ -27,6 +27,65 @@ with Sinfo.Nodes; use Sinfo.Nodes;
 
 package Sinfo.Utils is
 
+   --  We would like to get rid of the Library_Unit field, and replace it with
+   --  Other_Comp_Unit (on N_Compilation_Unit), Withed_Lib_Unit (on
+   --  N_With_Clause), and Subunit (on N_Body_Stub). Or we could split
+   --  Other_Comp_Unit into Spec_Lib_Unit, Body_Lib_Unit, Subunit_Parent.
+   --  However, gnat-llvm, codepeer, and spark are still using Library_Unit.
+   --  Therefore, we use the wrappers below.
+   --
+   --  The call site should always know whether it has an N_Compilation_Unit,
+   --  N_Body_Stub, or N_With_Clause. In the N_Compilation_Unit case, it should
+   --  also know whether it's looking for the spec of a body, the body of a
+   --  spec, or the parent of a subunit. Spec_Or_Body_Lib_Unit and
+   --  Other_Comp_Unit should be avoided when possible; these are for the
+   --  N_Compilation_Unit cases where the call site does NOT know what it's
+   --  looking for.
+
+   function Spec_Lib_Unit
+     (N : N_Compilation_Unit_Id) return Opt_N_Compilation_Unit_Id;
+   procedure Set_Spec_Lib_Unit (N, Val : N_Compilation_Unit_Id);
+   --  The spec compilation unit of a body compilation unit.
+   --  It can be an acts-as-spec subprogram body; in that case
+   --  Spec_Lib_Unit points to itself.
+
+   function Body_Lib_Unit
+     (N : N_Compilation_Unit_Id) return Opt_N_Compilation_Unit_Id;
+   procedure Set_Body_Lib_Unit (N, Val : N_Compilation_Unit_Id);
+   --  The body compilation unit of a spec compilation unit.
+   --  Empty if not present.
+
+   function Spec_Or_Body_Lib_Unit
+     (N : N_Compilation_Unit_Id) return Opt_N_Compilation_Unit_Id;
+   --  Same as Spec_Lib_Unit or Body_Lib_Unit, depending on whether
+   --  N is a body or spec. Used when we know N is a library unit
+   --  (not a subunit), but we don't know whether it's the spec
+   --  or the body.
+
+   function Subunit_Parent
+     (N : N_Compilation_Unit_Id) return Opt_N_Compilation_Unit_Id;
+   procedure Set_Subunit_Parent (N, Val : N_Compilation_Unit_Id);
+   --  The parent body of a subunit
+
+   function Other_Comp_Unit
+     (N : N_Compilation_Unit_Id) return Opt_N_Compilation_Unit_Id;
+   --  Same as Spec_Lib_Unit, Body_Lib_Unit, or Subunit_Parent,
+   --  as appropriate. Used when we don't know whether N is a
+   --  a library unit spec, library unit body, or subunit.
+
+   function Stub_Subunit (N : N_Body_Stub_Id) return Opt_N_Compilation_Unit_Id;
+   procedure Set_Stub_Subunit
+     (N : N_Body_Stub_Id; Val : N_Compilation_Unit_Id);
+   --  Subunit corresponding to a stub
+
+   function Withed_Lib_Unit
+     (N : N_With_Clause_Id) return Opt_N_Compilation_Unit_Id;
+   procedure Set_Withed_Lib_Unit
+     (N : N_With_Clause_Id; Val : N_Compilation_Unit_Id);
+   --  The compilation unit that a with clause refers to.
+   --  Note that the Sem_Elab creates with clauses that point to bodies
+   --  (including non-Acts_As_Spec bodies).
+
    -------------------------------
    -- Parent-related operations --
    -------------------------------
@@ -54,9 +113,9 @@ package Sinfo.Utils is
    -- Miscellaneous Tree Access Subprograms --
    -------------------------------------------
 
-   function First_Real_Statement -- ????
+   function First_Real_Statement -- ???
      (Ignored : N_Handled_Sequence_Of_Statements_Id) return Node_Id is (Empty);
-   --  The First_Real_Statement field is going away, but it is referenced in
+   --  The First_Real_Statement field has been removed, but it is referenced in
    --  codepeer and gnat-llvm. This is a temporary version, always returning
    --  Empty, to ease the transition.