utils.c (convert): Add comment and do not fall through to the next case.

	* gcc-interface/utils.c (convert) <RECORD_TYPE>: Add comment and do
	not fall through to the next case.
	<ARRAY_TYPE>: Deal specially with a dereference from another array
	type with the same element type.

From-SVN: r254618

gcc/ada/ChangeLog

+2017-11-10  Eric Botcazou  <ebotcazou@adacore.com>
+
+	* gcc-interface/utils.c (convert) <RECORD_TYPE>: Add comment and do
+	not fall through to the next case.
+	<ARRAY_TYPE>: Deal specially with a dereference from another array
+	type with the same element type.
+
 2017-11-09  Gary Dismukes  <dismukes@adacore.com>
 
 	* exp_util.adb, freeze.adb: Minor reformatting.

gcc/ada/gcc-interface/utils.c

@@ -4706,6 +4706,7 @@ convert (tree type, tree expr)
       return fold (convert_to_real (type, expr));
 
     case RECORD_TYPE:
+      /* Do a normal conversion between scalar and justified modular type.  */
       if (TYPE_JUSTIFIED_MODULAR_P (type) && !AGGREGATE_TYPE_P (etype))
 	{
 	  vec<constructor_elt, va_gc> *v;
@@ -4717,9 +4718,27 @@ convert (tree type, tree expr)
 	  return gnat_build_constructor (type, v);
 	}
 
-      /* ... fall through ... */
+      /* In these cases, assume the front-end has validated the conversion.
+	 If the conversion is valid, it will be a bit-wise conversion, so
+	 it can be viewed as an unchecked conversion.  */
+      return unchecked_convert (type, expr, false);
 
     case ARRAY_TYPE:
+      /* Do a normal conversion between unconstrained and constrained array
+	 type, assuming the latter is a constrained version of the former.  */
+      if (TREE_CODE (expr) == INDIRECT_REF
+	  && ecode == ARRAY_TYPE
+	  && TREE_TYPE (etype) == TREE_TYPE (type))
+	{
+	  tree ptr_type = build_pointer_type (type);
+	  tree t = build_unary_op (INDIRECT_REF, NULL_TREE,
+				   fold_convert (ptr_type,
+						 TREE_OPERAND (expr, 0)));
+	  TREE_READONLY (t) = TREE_READONLY (expr);
+	  TREE_THIS_NOTRAP (t) = TREE_THIS_NOTRAP (expr);
+	  return t;
+	}
+
       /* In these cases, assume the front-end has validated the conversion.
 	 If the conversion is valid, it will be a bit-wise conversion, so
 	 it can be viewed as an unchecked conversion.  */

gcc/testsuite/ChangeLog

+2017-11-10  Eric Botcazou  <ebotcazou@adacore.com>
+
+	* gnat.dg/opt69.adb: New test.
+
 2017-11-10  Jakub Jelinek  <jakub@redhat.com>
 
 	PR rtl-optimization/82913

gcc/testsuite/gnat.dg/opt69.adb

+-- { dg-do compile }
+-- { dg-options "-O" }
+
+with Ada.Text_IO;
+
+procedure Opt69 is
+
+   procedure Inner
+     (A : String := (1 .. 15 => ASCII.NUL);
+      B : String := (1 .. 5 => ASCII.NUL);
+      C : String := (1 .. 5 => ASCII.NUL))
+   is
+      Aa : String (1 .. 15);
+      Bb : String (1 .. 5);
+      Cc : String (1 .. 5);
+   begin
+      Aa := A;
+      Bb := B;
+      Cc := C;
+
+      Ada.Text_IO.Put_Line (Aa);
+      Ada.Text_IO.Put_Line (Bb);
+      Ada.Text_IO.Put_Line (Cc);
+   end;
+
+begin
+   Inner;
+end;