DWARF: add a language hook to override types in debugging information

Many artificial types are introduced by GNAT in order to satisfy
constraints in GCC's internal trees or to generate optimal code.  These
hide original types from sources and miss useful information in the
debugging information or add noise to it and make debugging confusing.
This change introduces a new language hook to give a chance to
front-ends to restore the source types in the debugging information.

This change also enhance the array descriptor language hook to handle
array-wide bit/byte stride.  Some arrays may contain dynamically-sized
objects.  Debuggers need for these a hint to know the size allocated for
each element, hence the need for the array-wide bit/byte stride.

The Ada front-end is enhanced to take advantage of both hooks when
-fgnat-encodings=minimal, in order to keep compatibility with GDB.

gcc/ada/ChangeLog:

	* gcc-interface/ada-tree.h (struct lang_type): Rename the t
	field as t1 and add a t2 one.
	(get_lang_specific): New.
	(GET_TYPE_LANG_SPECIFIC): Refactor to use get_lang_specific.
	(SET_TYPE_LANG_SPECIFIC): Likewise.
	(GET_TYPE_LANG_SPECIFIC2): New macro.
	(SET_TYPE_LANG_SPECIFIC2): New macro.
	(TYPE_DEBUG_TYPE): New macro.
	(SET_TYPE_DEBUG_TYPE): New macro.
	* gcc-interface/decl.c (gnat_to_gnu_entity): When
	-fgnat-encodings=minimal, set padding types' debug type to the
	padded one (i.e. strip ___PAD GNAT encodings) and set
	constrained record subtypes's debug type to the base type.
	* gcc-interface/misc.c (gnat_print_type): Print debug types.
	(gnat_get_debug_type): New.
	(gnat_get_array_descr_info): When -fgnat-encodings=minimal, set
	a byte stride for arrays that contain a type whose debug type
	has variable length.
	(LANG_HOOKS_GET_DEBUG_TYPE): Redefine macro to implement the
	debug type language hook.
	* gcc-interface/utils.c (maybe_pad_type): When
	-fgnat-encodings=minimal, set padding types' debug type to the
	padded one.  Restore XVZ variables creation when
	-fgnat-encodings-minimal and use them to hold padding types'
	byte size.  For library-level padding types, share this variable
	across translation units.  Tag XVZ variables as artificial.

gcc/ChangeLog:

	* langhooks.h (struct lang_hooks_for_types): Add a
	get_debug_type field.
	* langhooks-def.h (LANG_HOOKS_GET_DEBUG_TYPE): New macro.
	(LANG_HOOKS_FOR_TYPES_INITIALIZER): Initialize the
	get_debug_type field.
	* dwarf2out.h (struct array_descr_info): Add an array-wide
	stride field.
	* dwarf2out.c (modified_type_die): Invoke the get_debug_type
	language hook, process its result instead, if any.
	(gen_descr_array_type_die): Add array-wide stride processing.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@231763 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 25 insertions, 17 deletions

diff --git a/gcc/ada/gcc-interface/utils.c b/gcc/ada/gcc-interface/utils.c
index 830a0b8003e8..1816f3a9a264 100644
--- a/gcc/ada/gcc-interface/utils.c
+++ b/gcc/ada/gcc-interface/utils.c
@@ -1278,6 +1278,8 @@ maybe_pad_type (tree type, tree size, unsigned int align,
      type and name.  */
   record = make_node (RECORD_TYPE);
   TYPE_PADDING_P (record) = 1;
+  if (gnat_encodings == DWARF_GNAT_ENCODINGS_MINIMAL)
+    SET_TYPE_DEBUG_TYPE (record, type);
 
   if (Present (gnat_entity))
     TYPE_NAME (record) = create_concat_name (gnat_entity, "PAD");
@@ -1348,10 +1350,8 @@ maybe_pad_type (tree type, tree size, unsigned int align,
 
   /* Unless debugging information isn't being written for the input type,
      write a record that shows what we are a subtype of and also make a
-     variable that indicates our size, if still variable.  Don't do this if
-     asked to output as few encodings as possible.  */
-  if (gnat_encodings != DWARF_GNAT_ENCODINGS_MINIMAL
-      && TREE_CODE (orig_size) != INTEGER_CST
+     variable that indicates our size, if still variable.  */
+  if (TREE_CODE (orig_size) != INTEGER_CST
       && TYPE_NAME (record)
       && TYPE_NAME (type)
       && !(TREE_CODE (TYPE_NAME (type)) == TYPE_DECL
@@ -1367,6 +1367,8 @@ maybe_pad_type (tree type, tree size, unsigned int align,
 	  && TREE_CODE (size) != INTEGER_CST
 	  && (definition || global_bindings_p ()))
 	{
+	  /* Whether or not gnat_entity comes from source, this XVZ variable is
+	     is a compilation artifact.  */
 	  size_unit
 	    = create_var_decl (concat_name (name, "XVZ"), NULL_TREE, sizetype,
 			      size_unit, true, global_bindings_p (),
@@ -1375,19 +1377,25 @@ maybe_pad_type (tree type, tree size, unsigned int align,
 	  TYPE_SIZE_UNIT (record) = size_unit;
 	}
 
-      tree marker = make_node (RECORD_TYPE);
-      tree orig_name = TYPE_IDENTIFIER (type);
-
-      TYPE_NAME (marker) = concat_name (name, "XVS");
-      finish_record_type (marker,
-			  create_field_decl (orig_name,
-					     build_reference_type (type),
-					     marker, NULL_TREE, NULL_TREE,
-					     0, 0),
-			  0, true);
-      TYPE_SIZE_UNIT (marker) = size_unit;
-
-      add_parallel_type (record, marker);
+      /* There is no need to show what we are a subtype of when outputting as
+	 few encodings as possible: regular debugging infomation makes this
+	 redundant.  */
+      if (gnat_encodings != DWARF_GNAT_ENCODINGS_MINIMAL)
+	{
+	  tree marker = make_node (RECORD_TYPE);
+	  tree orig_name = TYPE_IDENTIFIER (type);
+
+	  TYPE_NAME (marker) = concat_name (name, "XVS");
+	  finish_record_type (marker,
+			      create_field_decl (orig_name,
+						 build_reference_type (type),
+						 marker, NULL_TREE, NULL_TREE,
+						 0, 0),
+			      0, true);
+	  TYPE_SIZE_UNIT (marker) = size_unit;
+
+	  add_parallel_type (record, marker);
+	}
     }
 
   rest_of_record_type_compilation (record);