utils.c (unchecked_convert): Tweak comment.

	* gcc-interface/utils.c (unchecked_convert): Tweak comment.  Only skip
	dereferences when padding to have the same size on both sides.  Do it
	for destination types with self-referential size too.

From-SVN: r272821

gcc/ada/ChangeLog

 2019-06-29  Eric Botcazou  <ebotcazou@adacore.com>
 
+	* gcc-interface/utils.c (unchecked_convert): Tweak comment.  Only skip
+	dereferences when padding to have the same size on both sides.  Do it
+	for destination types with self-referential size too.
+
+2019-06-29  Eric Botcazou  <ebotcazou@adacore.com>
+
 	* gcc-interface/decl.c (gnat_to_gnu_entity) <E_Record_Type>: If the
 	type requires strict alignment, then set the RM size to the type size.
 	Rework handling of alignment and sizes of tagged types in ASIS mode.

gcc/ada/gcc-interface/utils.c

@@ -5265,8 +5265,8 @@ unchecked_convert (tree type, tree expr, bool notrunc_p)
   if (etype == type)
     return expr;
 
-  /* If both types are integral just do a normal conversion.
-     Likewise for a conversion to an unconstrained array.  */
+  /* If both types are integral or regular pointer, then just do a normal
+     conversion.  Likewise for a conversion to an unconstrained array.  */
   if (((INTEGRAL_TYPE_P (type)
 	|| (POINTER_TYPE_P (type) && !TYPE_IS_THIN_POINTER_P (type))
 	|| (code == RECORD_TYPE && TYPE_JUSTIFIED_MODULAR_P (type)))
@@ -5397,14 +5397,16 @@ unchecked_convert (tree type, tree expr, bool notrunc_p)
      we need to pad to have the same size on both sides.
 
      ??? We cannot do it unconditionally because unchecked conversions are
-     used liberally by the front-end to implement polymorphism, e.g. in:
+     used liberally by the front-end to implement interface thunks:
 
+       type ada__tags__addr_ptr is access system.address;
        S191s : constant ada__tags__addr_ptr := ada__tags__addr_ptr!(S190s);
        return p___size__4 (p__object!(S191s.all));
 
-     so we skip all expressions that are references.  */
-  else if (!REFERENCE_CLASS_P (expr)
+     so we need to skip dereferences.  */
+  else if (!INDIRECT_REF_P (expr)
 	   && !AGGREGATE_TYPE_P (etype)
+	   && ecode != UNCONSTRAINED_ARRAY_TYPE
 	   && TREE_CONSTANT (TYPE_SIZE (type))
 	   && (c = tree_int_cst_compare (TYPE_SIZE (etype), TYPE_SIZE (type))))
     {
@@ -5424,6 +5426,31 @@ unchecked_convert (tree type, tree expr, bool notrunc_p)
 	}
     }
 
+  /* Likewise if we are converting from a scalar type to a type with self-
+     referential size.  We use the max size to do the padding in this case.  */
+  else if (!INDIRECT_REF_P (expr)
+	   && !AGGREGATE_TYPE_P (etype)
+	   && ecode != UNCONSTRAINED_ARRAY_TYPE
+	   && CONTAINS_PLACEHOLDER_P (TYPE_SIZE (type)))
+    {
+      tree new_size = max_size (TYPE_SIZE (type), true);
+      c = tree_int_cst_compare (TYPE_SIZE (etype), new_size);
+      if (c < 0)
+	{
+	  expr = convert (maybe_pad_type (etype, new_size, 0, Empty,
+					  false, false, false, true),
+			  expr);
+	  expr = unchecked_convert (type, expr, notrunc_p);
+	}
+      else
+	{
+	  tree rec_type = maybe_pad_type (type, TYPE_SIZE (etype), 0, Empty,
+					  false, false, false, true);
+	  expr = unchecked_convert (rec_type, expr, notrunc_p);
+	  expr = build_component_ref (expr, TYPE_FIELDS (rec_type), false);
+	}
+    }
+
   /* We have a special case when we are converting between two unconstrained
      array types.  In that case, take the address, convert the fat pointer
      types, and dereference.  */

gcc/testsuite/ChangeLog

 2019-06-29  Eric Botcazou  <ebotcazou@adacore.com>
 
+	* gnat.dg/specs/unchecked_convert1.ads: New test.
+	* gnat.dg/specs/unchecked_convert2.ads: Likewise.
+
+2019-06-29  Eric Botcazou  <ebotcazou@adacore.com>
+
 	* gnat.dg/specs/size_clause3.ads: Adjust error message.
 
 2019-06-29  Eric Botcazou  <ebotcazou@adacore.com>

gcc/testsuite/gnat.dg/specs/unchecked_convert1.ads

+-- { dg-do compile }
+-- { dg-options "-gnatws" }
+
+with Ada.Unchecked_Conversion;
+with System;
+
+package Unchecked_Convert1 is
+
+  type Rec (D : Boolean := False) is record
+    case D is
+      when True => I : Integer;
+      when False => null;
+    end case;
+  end record;
+
+  function To_Rec is new Ada.Unchecked_Conversion (System.Address, Rec);
+
+  function F (A : System.Address) return Rec is (To_Rec (A));
+
+end Unchecked_Convert1;

gcc/testsuite/gnat.dg/specs/unchecked_convert2.ads

+-- { dg-do compile }
+-- { dg-options "-gnatws" }
+
+with Ada.Unchecked_Conversion;
+
+package Unchecked_Convert2 is
+
+  type Address is access String;
+  for Address'Size use Standard'Address_Size;
+
+  type Rec is record
+    A : Address;
+  end record;
+
+  function To_Integer is new Ada.Unchecked_Conversion (Address, Integer);
+
+  function F (R : Rec) return Integer is (To_Integer (R.A));
+
+end Unchecked_Convert2;