This partially relaxes alignment constraint for tagged types on x86 and, more
generally, architectures that do not require strict alignment for memory
accesses, for historical reasons: the compiler now accepts size clauses on
record type extensions that effectively lower the alignment of the type, if
there is also a representation clause on the type.
Tested on x86_64-suse-linux, applied on the mainline.
2017-05-15 Eric Botcazou <ebotca...@adacore.com>
* gcc-interface/decl.c (gnat_to_gnu_entity) <E_Record_Type>: Whenthere
is a representation clause on an extension, propagate the alignment of
the parent type only if the platform requires strict alignment.
--
Eric BotcazouIndex: gcc-interface/decl.c
===================================================================
--- gcc-interface/decl.c (revision 247951)
+++ gcc-interface/decl.c (working copy)
@@ -204,6 +204,7 @@ static tree elaborate_expression_2 (tree
static tree elaborate_reference (tree, Entity_Id, bool, tree *);
static tree gnat_to_gnu_component_type (Entity_Id, bool, bool);
static tree gnat_to_gnu_subprog_type (Entity_Id, bool, bool, tree *);
+static int adjust_packed (tree, tree, int);
static tree gnat_to_gnu_field (Entity_Id, tree, int, bool, bool);
static tree gnu_ext_name_for_subprog (Entity_Id, tree);
static tree change_qualified_type (tree, int);
@@ -3094,6 +3095,7 @@ gnat_to_gnu_entity (Entity_Id gnat_entit
Entity_Id gnat_parent = Parent_Subtype (gnat_entity);
tree gnu_dummy_parent_type = make_node (RECORD_TYPE);
tree gnu_parent;
+ int parent_packed = 0;
/* A major complexity here is that the parent subtype will
reference our discriminants in its Stored_Constraint list.
@@ -3172,7 +3174,17 @@ gnat_to_gnu_entity (Entity_Id gnat_entit
be created with a component clause below, then we need
to apply the same adjustment as in gnat_to_gnu_field. */
if (has_rep && TYPE_ALIGN (gnu_type) < TYPE_ALIGN (gnu_parent))
- SET_TYPE_ALIGN (gnu_type, TYPE_ALIGN (gnu_parent));
+ {
+ /* ??? For historical reasons, we do it on strict-alignment
+ platforms only, where it is really required. This means
+ that a confirming representation clause will change the
+ behavior of the compiler on the other platforms. */
+ if (STRICT_ALIGNMENT)
+ SET_TYPE_ALIGN (gnu_type, TYPE_ALIGN (gnu_parent));
+ else
+ parent_packed
+ = adjust_packed (gnu_parent, gnu_type, parent_packed);
+ }
/* Finally we fix up both kinds of twisted COMPONENT_REF we have
initially built. The discriminants must reference the fields
@@ -3218,7 +3230,7 @@ gnat_to_gnu_entity (Entity_Id gnat_entit
? TYPE_SIZE (gnu_parent) : NULL_TREE,
has_rep
? bitsize_zero_node : NULL_TREE,
- 0, 1);
+ parent_packed, 1);
DECL_INTERNAL_P (gnu_field) = 1;
TREE_OPERAND (gnu_get_parent, 1) = gnu_field;
TYPE_FIELDS (gnu_type) = gnu_field;
