[Ada] Spurious warning on call with out parameter in expression function

2019-10-10  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_warn.adb (Warn_On_Useless_Assignment): Do not warn if the
	second assignment is at the same source position as the first.

From-SVN: r276831

gcc/ada/ChangeLog

-2019-10-10  Gary Dismukes  <dismukes@adacore.com>
+2019-10-10  Ed Schonberg  <schonberg@adacore.com>
 
-	* sem_util.adb (Enclosing_Subprogram): Handle the case of
-	E_Entry_Family, returning the entry family's associated
-	Protected_Body_Subprogram (as was already done for E_Entry).
-	* exp_ch9.adb (Expand_N_Accept_Statement): Call Reset_Scopes_To
-	on the block created for an accept statement to reset the scopes
-	of any local entities to the block scope.
\ No newline at end of file
+	* sem_warn.adb (Warn_On_Useless_Assignment): Do not warn if the
+	second assignment is at the same source position as the first.
\ No newline at end of file

gcc/ada/sem_warn.adb

@@ -4546,9 +4546,15 @@ package body Sem_Warn is
       --  to capture the value. We are not going to capture any value, but
       --  the warning message depends on the same kind of conditions.
 
+      --  If the assignment appears as an out-parameter in a call within an
+      --  expression function it may be detected twice: once when expression
+      --  itself is analyzed, and once when the constructed body is analyzed.
+      --  We don't want to emit a spurious warning in this case.
+
       if Is_Assignable (Ent)
         and then not Is_Return_Object (Ent)
         and then Present (Last_Assignment (Ent))
+        and then Last_Assignment (Ent) /= N
         and then not Is_Imported (Ent)
         and then not Is_Exported (Ent)
         and then Safe_To_Capture_Value (N, Ent)