utils.c (max_size): Add special code to deal with the subtraction of a "negative" value in an...

	* gcc-interface/utils.c (max_size) <tcc_binary>: Add special code to
	deal with the subtraction of a "negative" value in an unsigned type.

From-SVN: r223837

gcc/ada/ChangeLog

 2015-05-28  Eric Botcazou  <ebotcazou@adacore.com>
 
+	* gcc-interface/utils.c (max_size) <tcc_binary>: Add special code to
+	deal with the subtraction of a "negative" value in an unsigned type.
+
+2015-05-28  Eric Botcazou  <ebotcazou@adacore.com>
+
 	* gcc-interface/decl.c (gnat_to_gnu_entity) <E_Subprogram_Type>: Do
 	not error out on a return type which has a size that overflows if the
 	return is done by invisible reference.

gcc/ada/gcc-interface/utils.c

@@ -3443,9 +3443,23 @@ max_size (tree exp, bool max_p)
 	if ((code == MINUS_EXPR || code == PLUS_EXPR)
 	    && TREE_CODE (lhs) == INTEGER_CST
 	    && TREE_OVERFLOW (lhs)
-	    && !TREE_CONSTANT (rhs))
+	    && TREE_CODE (rhs) != INTEGER_CST)
 	  return lhs;
 
+	/* If we are going to subtract a "negative" value in an unsigned type,
+	   do the operation as an addition of the negated value, in order to
+	   avoid creating a spurious overflow below.  */
+	if (code == MINUS_EXPR
+	    && TYPE_UNSIGNED (type)
+	    && TREE_CODE (rhs) == INTEGER_CST
+	    && !TREE_OVERFLOW (rhs)
+	    && tree_int_cst_sign_bit (rhs) != 0)
+	  {
+	    rhs = fold_build1 (NEGATE_EXPR, type, rhs);
+	    code = PLUS_EXPR;
+	  }
+
+	/* We need to detect overflows so we call size_binop here.  */
 	return size_binop (code, lhs, rhs);
       }
 

gcc/testsuite/ChangeLog

 2015-05-28  Eric Botcazou  <ebotcazou@adacore.com>
 
+	* gnat.dg/discr43.adb: New test.
+
+2015-05-28  Eric Botcazou  <ebotcazou@adacore.com>
+
 	* gnat.dg/varsize_temp.adb: Rename into...
 	* gnat.dg/varsize1.adb: ...this.
 	* gnat.dg/varsize_copy.ad[sb]: Rename into...

gcc/testsuite/gnat.dg/discr43.adb

+-- { dg-do compile }
+
+with Text_IO; use Text_IO;
+
+procedure Discr43 is
+
+  type Arr is array (Short_Integer range <>) of Boolean;
+
+  type Rec (LB : Short_Integer; UB : Short_Integer) is record
+    A : Arr (LB .. UB);
+  end record;
+
+begin
+  Put_Line ("Arr'Max_Size =" & Arr'Max_Size_In_Storage_Elements'Img);
+  Put_Line ("Rec'Max_Size =" & Rec'Max_Size_In_Storage_Elements'Img);
+end;