Fix uniqueness of address for aliased objects

Two aliased objects must have distinct addresses, even if they have
size zero, so we make sure to allocate at least one byte for them.

	* gcc-interface/decl.c (gnat_to_gnu_entity) <E_Variable>: Force at
	least the unit size for an aliased object of a constrained nominal
	subtype whose size is variable.

1 files changed, 12 insertions, 3 deletions

diff --git a/gcc/ada/gcc-interface/decl.c b/gcc/ada/gcc-interface/decl.c
index a4053ee..9c1acd9 100644
--- a/gcc/ada/gcc-interface/decl.c
+++ b/gcc/ada/gcc-interface/decl.c
@@ -969,10 +969,19 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, bool definition)
 	  align = MINIMUM_ATOMIC_ALIGNMENT;
 #endif
 
-	/* Make a new type with the desired size and alignment, if needed.
-	   But do not take into account alignment promotions to compute the
-	   size of the object.  */
+	/* Do not take into account aliased adjustments or alignment promotions
+	   to compute the size of the object.  */
 	tree gnu_object_size = gnu_size ? gnu_size : TYPE_SIZE (gnu_type);
+
+	/* If the object is aliased, of a constrained nominal subtype and its
+	   size might be zero at run time, we force at least the unit size.  */
+	if (Is_Aliased (gnat_entity)
+	    && !Is_Constr_Subt_For_UN_Aliased (gnat_type)
+	    && Is_Array_Type (Underlying_Type (gnat_type))
+	    && !TREE_CONSTANT (gnu_object_size))
+	  gnu_size = size_binop (MAX_EXPR, gnu_object_size, bitsize_unit_node);
+
+	/* Make a new type with the desired size and alignment, if needed.  */
 	if (gnu_size || align > 0)
 	  {
 	    tree orig_type = gnu_type;