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.

diff --git a/gcc/ada/ChangeLog b/gcc/ada/ChangeLog
index 9644e018f3e825f3768a573233fec30ea6779996..35d111401e2923a33695300690f2244b2f010af1 100644 (file)
--- a/gcc/ada/ChangeLog
+++ b/gcc/ada/ChangeLog
@@ -1,3 +1,9 @@
+2020-05-08  Eric Botcazou  <ebotcazou@adacore.com>
+
+       * 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.
+
 2020-05-08  Eric Botcazou  <ebotcazou@adacore.com>
 
        * gcc-interface/decl.c (gnat_to_gnu_entity) <E_Array_Subtype>: Deal

diff --git a/gcc/ada/gcc-interface/decl.c b/gcc/ada/gcc-interface/decl.c
index a4053eec8397cc5dd785505da5d3ee0e5ae1786a..9c1acd9f23f4532debaf76bdf84cc6a6affa7e4f 100644 (file)
--- 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;

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index adacf69b027e54d4158c8dd7e6932ccce0d20ddd..8dc87d3948de3eba032b42c9d2b6343f8dd432c1 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2020-05-08  Eric Botcazou  <ebotcazou@adacore.com>
+
+       * gnat.dg/addr15.adb: New test.
+
 2020-05-08  Richard Biener  <rguenther@suse.de>
 
        * gnat.dg/opt83.adb: New testcase.

diff --git a/gcc/testsuite/gnat.dg/addr15.adb b/gcc/testsuite/gnat.dg/addr15.adb
new file mode 100644 (file)
index 0000000..bb79dff
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/addr15.adb
@@ -0,0 +1,19 @@
+--  { dg-do run }
+
+with System; use System;
+
+procedure Addr15 is
+
+  function Get_Bound (Param : Integer) return Integer is (Param);
+
+  type Alpha_Typ is array (1 .. Get_Bound (1)) of Integer;
+  type Beta_Typ  is array (1 .. Get_Bound (0)) of Integer;
+
+  Alpha : Alpha_Typ;
+  Beta  : aliased Beta_Typ;
+
+begin
+  if Alpha'Address = Beta'Address then
+    raise Program_Error;
+  end if;
+end;