[Ada] Suppress Initialize_Scalars for Persistent_BSS

[Ada] Suppress Initialize_Scalars for Persistent_BSS

[Pierre-Marie de Rodat]

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If a variable has pragma Persistent_BSS, the compiler now automatically
suppresses implicit initializations caused by Initialize_Scalars and
Normalize_Scalars. Variables with Persistent_BSS cannot be initialized,
and previously a pragma Suppress_Initialization was required before the
pragma Persistent_BSS.

Tested on x86_64-pc-linux-gnu, committed on trunk

2019-08-20  Bob Duff  <duff@adacore.com>

gcc/ada/

	* sem_prag.adb (Persistent_BSS): If an initialization is present
	because of Initialize_Scalars or Normalize_Scalars, generate an
	implicit pragma Suppress_Initialization to remove that, because
	initialization is not allowed for these variables. Other
	initializations remain illegal.

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--- gcc/ada/sem_prag.adb
+++ gcc/ada/sem_prag.adb
@@ -21092,8 +21092,24 @@ package body Sem_Prag is
                Decl := Parent (Ent);
 
                if Present (Expression (Decl)) then
-                  Error_Pragma_Arg
-                    ("object for pragma% cannot have initialization", Arg1);
+                  --  Variables in Persistent_BSS cannot be initialized, so
+                  --  turn off any initialization that might be caused by
+                  --  pragmas Initialize_Scalars or Normalize_Scalars.
+
+                  if Kill_Range_Check (Expression (Decl)) then
+                     Prag :=
+                       Make_Pragma (Loc,
+                         Name_Suppress_Initialization,
+                         Pragma_Argument_Associations => New_List (
+                           Make_Pragma_Argument_Association (Loc,
+                             Expression => New_Occurrence_Of (Ent, Loc))));
+                     Insert_Before (N, Prag);
+                     Analyze (Prag);
+
+                  else
+                     Error_Pragma_Arg
+                       ("object for pragma% cannot have initialization", Arg1);
+                  end if;
                end if;
 
                if not Is_Potentially_Persistent_Type (Etype (Ent)) then
@@ -21104,7 +21120,7 @@ package body Sem_Prag is
 
                Prag :=
                  Make_Linker_Section_Pragma
-                   (Ent, Sloc (N), ".persistent.bss");
+                   (Ent, Loc, ".persistent.bss");
                Insert_After (N, Prag);
                Analyze (Prag);