Re: [Ada] Use C++-compatible calling convention on x86/Windows

[Eric Botcazou <ebotcazou at adacore dot com>]

> Now reverted, including on the 4.7 branch (this is only for x86/Windows). 
> We have decided to use another approach to deal with the problem as the
> above one introduces backwards compatibily issues.

This is the new approach, which doesn't require modifications to the source 
code and essentially replicates the separation between methods and non-methods
that doesn't exist in Ada.

Tested on i586-suse-linux, applied on mainline and 4.7 branch.


2012-07-03  Eric Botcazou  <ebotcazou@adacore.com>

	* exp_disp.adb (Expand_Dispatching_Call): Propagate the convention on
	the designated subprogram type and also set Is_Dispatch_Table_Entity.
	(Expand_Interface_Thunk): Propagate the convention on the thunk.
	(Set_CPP_Constructors_Old): Set Is_Constructor and Convention_CPP on
	the internal view of the constructors.
	(Set_CPP_Constructors): Likewise.
	* sem_prag.adb (Analyze_Pragma) <Pragma_CPP_Constructor>: Set the
	convention on the function.
     	* gcc-interface/gigi.h (is_cplusplus_method): Declare.
	* gcc-interface/decl.c (Has_Thiscall_Convention): New macro.
	(gnat_to_gnu_entity) <E_Subprogram_Type>: Test it to set the `thiscall'
	calling convention
	(get_minimal_subprog_decl): Likewise.
	(is_cplusplus_method): New predicate.
	* gcc-interface/trans.c (Attribute_to_gnu) <Attr_Access>: Issue an
	error on access to C++ constructor or member function.

-- 
Eric Botcazou

Index: sem_prag.adb
===================================================================
--- sem_prag.adb	(revision 189034)
+++ sem_prag.adb	(working copy)
@@ -7865,6 +7865,7 @@ package body Sem_Prag is
 
                Set_Has_Completion (Def_Id);
                Set_Is_Constructor (Def_Id);
+               Set_Convention (Def_Id, Convention_CPP);
 
                --  Imported C++ constructors are not dispatching primitives
                --  because in C++ they don't have a dispatch table slot.
Index: exp_disp.adb
===================================================================
--- exp_disp.adb	(revision 189034)
+++ exp_disp.adb	(working copy)
@@ -803,6 +803,11 @@ package body Exp_Disp is
       Subp_Ptr_Typ := Create_Itype (E_Access_Subprogram_Type, Call_Node);
       Set_Etype          (Subp_Typ, Res_Typ);
       Set_Returns_By_Ref (Subp_Typ, Returns_By_Ref (Subp));
+      Set_Convention     (Subp_Typ, Convention (Subp));
+
+      --  Notify gigi that the designated type is a dispatching primitive
+
+      Set_Is_Dispatch_Table_Entity (Subp_Typ);
 
       --  Create a new list of parameters which is a copy of the old formal
       --  list including the creation of a new set of matching entities.
@@ -1850,6 +1855,7 @@ package body Exp_Disp is
 
       Thunk_Id := Make_Temporary (Loc, 'T');
       Set_Is_Thunk (Thunk_Id);
+      Set_Convention (Thunk_Id, Convention (Prim));
 
       --  Procedure case
 
@@ -8468,8 +8474,9 @@ package body Exp_Disp is
 
                Set_Init_Proc (Typ, Init);
                Set_Is_Imported    (Init);
+               Set_Is_Constructor (Init);
                Set_Interface_Name (Init, Interface_Name (E));
-               Set_Convention     (Init, Convention_C);
+               Set_Convention     (Init, Convention_CPP);
                Set_Is_Public      (Init);
                Set_Has_Completion (Init);
             end if;
@@ -8562,8 +8569,9 @@ package body Exp_Disp is
                   Parameter_Specifications => Parms));
 
             Set_Is_Imported    (Constructor_Id);
+            Set_Is_Constructor (Constructor_Id);
             Set_Interface_Name (Constructor_Id, Interface_Name (E));
-            Set_Convention     (Constructor_Id, Convention_C);
+            Set_Convention     (Constructor_Id, Convention_CPP);
             Set_Is_Public      (Constructor_Id);
             Set_Has_Completion (Constructor_Id);
 
Index: gcc-interface/decl.c
===================================================================
--- gcc-interface/decl.c	(revision 189034)
+++ gcc-interface/decl.c	(working copy)
@@ -50,19 +50,23 @@
 #include "ada-tree.h"
 #include "gigi.h"
 
-/* Convention_Stdcall should be processed in a specific way on 32 bits
-   Windows targets only.  The macro below is a helper to avoid having to
-   check for a Windows specific attribute throughout this unit.  */
+/* "stdcall" and "thiscall" conventions should be processed in a specific way
+   on 32-bit x86/Windows only.  The macros below are helpers to avoid having
+   to check for a Windows specific attribute throughout this unit.  */
 
 #if TARGET_DLLIMPORT_DECL_ATTRIBUTES
 #ifdef TARGET_64BIT
 #define Has_Stdcall_Convention(E) \
   (!TARGET_64BIT && Convention (E) == Convention_Stdcall)
+#define Has_Thiscall_Convention(E) \
+  (!TARGET_64BIT && is_cplusplus_method (E))
 #else
 #define Has_Stdcall_Convention(E) (Convention (E) == Convention_Stdcall)
+#define Has_Thiscall_Convention(E) (is_cplusplus_method (E))
 #endif
 #else
 #define Has_Stdcall_Convention(E) 0
+#define Has_Thiscall_Convention(E) 0
 #endif
 
 /* Stack realignment is necessary for functions with foreign conventions when
@@ -4413,6 +4417,11 @@ gnat_to_gnu_entity (Entity_Id gnat_entit
 	    (&attr_list, ATTR_MACHINE_ATTRIBUTE,
 	     get_identifier ("stdcall"), NULL_TREE,
 	     gnat_entity);
+	else if (Has_Thiscall_Convention (gnat_entity))
+	  prepend_one_attribute_to
+	    (&attr_list, ATTR_MACHINE_ATTRIBUTE,
+	     get_identifier ("thiscall"), NULL_TREE,
+	     gnat_entity);
 
 	/* If we should request stack realignment for a foreign convention
 	   subprogram, do so.  Note that this applies to task entry points in
@@ -5276,6 +5285,10 @@ get_minimal_subprog_decl (Entity_Id gnat
     prepend_one_attribute_to (&attr_list, ATTR_MACHINE_ATTRIBUTE,
 			      get_identifier ("stdcall"), NULL_TREE,
 			      gnat_entity);
+  else if (Has_Thiscall_Convention (gnat_entity))
+    prepend_one_attribute_to (&attr_list, ATTR_MACHINE_ATTRIBUTE,
+			      get_identifier ("thiscall"), NULL_TREE,
+			      gnat_entity);
 
   if (No (Interface_Name (gnat_entity)) && gnu_ext_name == gnu_entity_name)
     gnu_ext_name = NULL_TREE;
@@ -5285,6 +5298,39 @@ get_minimal_subprog_decl (Entity_Id gnat
 			 false, true, true, true, attr_list, gnat_entity);
 }
 
+/* Return whether the E_Subprogram_Type/E_Function/E_Procedure GNAT_ENTITY is
+   a C++ imported method or equivalent.
+
+   We use the predicate on 32-bit x86/Windows to find out whether we need to
+   use the "thiscall" calling convention for GNAT_ENTITY.  This convention is
+   used for C++ methods (functions with METHOD_TYPE) by the back-end.  */
+
+bool
+is_cplusplus_method (Entity_Id gnat_entity)
+{
+  if (Convention (gnat_entity) != Convention_CPP)
+    return False;
+
+  /* This is the main case: C++ method imported as a primitive operation.  */
+  if (Is_Dispatching_Operation (gnat_entity))
+    return True;
+
+  /* A thunk needs to be handled like its associated primitive operation.  */
+  if (Is_Subprogram (gnat_entity) && Is_Thunk (gnat_entity))
+    return True;
+
+  /* C++ classes with no virtual functions can be imported as limited
+     record types, but we need to return true for the constructors.  */
+  if (Is_Constructor (gnat_entity))
+    return True;
+
+  /* This is set on the E_Subprogram_Type built for a dispatching call.  */
+  if (Is_Dispatch_Table_Entity (gnat_entity))
+    return True;
+
+  return False;
+}
+
 /* Finalize the processing of From_With_Type incomplete types.  */
 
 void
Index: gcc-interface/gigi.h
===================================================================
--- gcc-interface/gigi.h	(revision 189034)
+++ gcc-interface/gigi.h	(working copy)
@@ -116,6 +116,10 @@ extern tree get_unpadded_type (Entity_Id
    alias is already present, in which case it is returned instead.  */
 extern tree get_minimal_subprog_decl (Entity_Id gnat_entity);
 
+/* Return whether the E_Subprogram_Type/E_Function/E_Procedure GNAT_ENTITY is
+   a C++ imported method or equivalent.  */
+extern bool is_cplusplus_method (Entity_Id gnat_entity);
+
 /* Create a record type that contains a SIZE bytes long field of TYPE with a
     starting bit position so that it is aligned to ALIGN bits, and leaving at
     least ROOM bytes free before the field.  BASE_ALIGN is the alignment the
Index: gcc-interface/trans.c
===================================================================
--- gcc-interface/trans.c	(revision 189034)
+++ gcc-interface/trans.c	(working copy)
@@ -1424,6 +1424,15 @@ Attribute_to_gnu (Node_Id gnat_node, tre
 	    TREE_NO_TRAMPOLINE (gnu_expr) = TREE_CONSTANT (gnu_expr) = 1;
 	}
 
+      /* For 'Access, issue an error message if the prefix is a C++ method
+	 since it can use a special calling convention on some platforms,
+	 which cannot be propagated to the access type.  */
+      else if (attribute == Attr_Access
+	       && Nkind (Prefix (gnat_node)) == N_Identifier
+	       && is_cplusplus_method (Entity (Prefix (gnat_node))))
+	post_error ("access to C++ constructor or member function not allowed",
+		    gnat_node);
+
       /* For other address attributes applied to a nested function,
 	 find an inner ADDR_EXPR and annotate it so that we can issue
 	 a useful warning with -Wtrampolines.  */