Reject components in extensions overlapping with the parent

Such problematic components can be specified by means of a component
clause but they cannot be fully supported by the type system.  They
had initially been forbidden, then we decided to accept them by working
around the type system, but this is very fragile and, for example, any
static aggregate is guaranteed to trigger an ICE with the current
implementation.

We now reject them again, except if the -gnatd.K switch is passed.

gcc/ada/ChangeLog:
	* debug.adb (d.K): Document new usage.
	* fe.h (Debug_Flag_Dot_KK): Declare.
	* gcc-interface/decl.c (gnat_to_gnu_field): Give an error when the
	component overlaps with the parent subtype, except with -gnatd.K.

diff --git a/gcc/ada/debug.adb b/gcc/ada/debug.adb
index 63b14b2bd6d466a257d067b57edf02bb1d0e6ca7..0f73c2a17ae95e82ab2b96180e89574347fcf148 100644 (file)
--- a/gcc/ada/debug.adb
+++ b/gcc/ada/debug.adb
@@ -128,7 +128,7 @@ package body Debug is
    --  d.H
    --  d.I  Do not ignore enum representation clauses in CodePeer mode
    --  d.J  Relaxed rules for pragma No_Return
-   --  d.K
+   --  d.K  Do not reject components in extensions overlapping with parent
    --  d.L  Depend on back end for limited types in if and case expressions
    --  d.M  Relaxed RM semantics
    --  d.N  Add node to all entities
@@ -898,6 +898,11 @@ package body Debug is
    --       for that. If the procedure does in fact return normally, execution
    --       is erroneous, and therefore unpredictable.
 
+   --  d.K  Do not reject components in extensions overlapping with the parent
+   --       component. Such components can be specified by means of a component
+   --       clause but they cannot be fully supported by the GCC type system.
+   --       This switch nevertheless allows them for the sake of compatibility.
+
    --  d.L  Normally the front end generates special expansion for conditional
    --       expressions of a limited type. This debug flag removes this special
    --       case expansion, leaving it up to the back end to handle conditional

diff --git a/gcc/ada/fe.h b/gcc/ada/fe.h
index 043300d42c9af07a2b54ea2c6000b8c3302fb8a1..463a89c5fdb768f69e92eb3280c3331f30214045 100644 (file)
--- a/gcc/ada/fe.h
+++ b/gcc/ada/fe.h
@@ -59,9 +59,11 @@ extern int Compiler_Abort (String_Pointer, String_Pointer, Boolean) ATTRIBUTE_NO
 
 /* debug: */
 
+#define Debug_Flag_Dot_KK      debug__debug_flag_dot_kk
 #define Debug_Flag_Dot_R       debug__debug_flag_dot_r
 #define Debug_Flag_NN          debug__debug_flag_nn
 
+extern Boolean Debug_Flag_Dot_KK;
 extern Boolean Debug_Flag_Dot_R;
 extern Boolean Debug_Flag_NN;
 

diff --git a/gcc/ada/gcc-interface/decl.c b/gcc/ada/gcc-interface/decl.c
index cad06a4dd0665e8c9e44aadba3d2877ad0fd2544..025714bd33946262de44ebefdff3532234f88c79 100644 (file)
--- a/gcc/ada/gcc-interface/decl.c
+++ b/gcc/ada/gcc-interface/decl.c
@@ -7234,12 +7234,12 @@ gnat_to_gnu_field (Entity_Id gnat_field, tree gnu_record_type, int packed,
     {
       Entity_Id gnat_parent = Parent_Subtype (gnat_record_type);
 
-      /* Ensure the position does not overlap with the parent subtype, if there
-        is one.  This test is omitted if the parent of the tagged type has a
-        full rep clause since, in this case, component clauses are allowed to
-        overlay the space allocated for the parent type and the front-end has
-        checked that there are no overlapping components.  */
-      if (Present (gnat_parent) && !Is_Fully_Repped_Tagged_Type (gnat_parent))
+      /* Ensure the position doesn't overlap with the parent subtype if there
+        is one.  It would be impossible to build CONSTRUCTORs and accessing
+        the parent could clobber the component in the extension if directly
+        done.  We accept it with -gnatd.K for the sake of compatibility.  */
+      if (Present (gnat_parent)
+         && !(Debug_Flag_Dot_KK && Is_Fully_Repped_Tagged_Type (gnat_parent)))
        {
          tree gnu_parent = gnat_to_gnu_type (gnat_parent);