[COMMITTED] ada: Support lock-free protected objects with pragma Initialize_Scalars

["Marc Poulhiès" <poulhies@adacore.com>]

From: Piotr Trojanek <trojanek@adacore.com>

In general, protected subprograms are only eligible for a lock-free
expansion if they do not reference global assignable objects.

However, it seems reasonable to ignore references to variables in
System.Scalar_Values, which are generated when pragma Initialize_Scalars
is active. Such references appear, for example, when protected
subprogram has formal parameters of mode out.

gcc/ada/

	* sem_ch9.adb (Satisfies_Lock_Free_Requirements): Ignore
	references to global variables inserted due to pragma
	Initialize_Scalars.

Tested on x86_64-pc-linux-gnu, committed on master.

---
 gcc/ada/sem_ch9.adb | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/gcc/ada/sem_ch9.adb b/gcc/ada/sem_ch9.adb
index 5dee216256c..e43e3ae0b41 100644
--- a/gcc/ada/sem_ch9.adb
+++ b/gcc/ada/sem_ch9.adb
@@ -474,6 +474,12 @@ package body Sem_Ch9 is
                      begin
                         --  Prohibit references to non-constant entities
                         --  outside the protected subprogram scope.
+                        --
+                        --  References to variables in System.Scalar_Values
+                        --  generated because of pragma Initialize_Scalars are
+                        --  allowed, because once those variables are
+                        --  initialized by the binder-generated code, they
+                        --  behave like constants.
 
                         if Is_Assignable (Id)
                           and then not
@@ -482,6 +488,9 @@ package body Sem_Ch9 is
                             Scope_Within_Or_Same
                               (Scope (Id),
                                Protected_Body_Subprogram (Sub_Id))
+                          and then not
+                            (Is_RTU (Scope (Id), System_Scalar_Values)
+                               and then not Comes_From_Source (N))
                         then
                            if Lock_Free_Given then
                               Error_Msg_NE
-- 
2.34.1