[Ada] Reference in Unbounded_String is almost never null

[Ada] Reference in Unbounded_String is almost never null

[Pierre-Marie de Rodat]

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There are two variants of the Ada.Strings.Unbounded_String package, with
and without atomic reference counters. The underlying pointer is never
null in one variant (and had a null-excluding type) and almost never
null in the other variant (and now has a null-excluding type as well).

Cleanup related to sync of contracts for GNATprove between both variants
of the package.

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

gcc/ada/

	* libgnat/a-strunb.ads (Unbounded_String): Reference is never
	null.
	* libgnat/a-strunb.adb (Finalize): Copy reference while it needs
	to be deallocated.

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diff --git a/gcc/ada/libgnat/a-strunb.adb b/gcc/ada/libgnat/a-strunb.adb
--- a/gcc/ada/libgnat/a-strunb.adb
+++ b/gcc/ada/libgnat/a-strunb.adb
@@ -505,8 +505,14 @@ package body Ada.Strings.Unbounded is
       --  Note: Don't try to free statically allocated null string
 
       if Object.Reference /= Null_String'Access then
-         Deallocate (Object.Reference);
-         Object.Reference := Null_Unbounded_String.Reference;
+         declare
+            Reference_Copy : String_Access := Object.Reference;
+            --  The original reference cannot be null, so we must create a
+            --  copy which will become null when deallocated.
+         begin
+            Deallocate (Reference_Copy);
+            Object.Reference := Null_Unbounded_String.Reference;
+         end;
          Object.Last := 0;
       end if;
    end Finalize;


diff --git a/gcc/ada/libgnat/a-strunb.ads b/gcc/ada/libgnat/a-strunb.ads
--- a/gcc/ada/libgnat/a-strunb.ads
+++ b/gcc/ada/libgnat/a-strunb.ads
@@ -746,8 +746,8 @@ private
      renames To_Unbounded_String;
 
    type Unbounded_String is new AF.Controlled with record
-      Reference : String_Access := Null_String'Access;
-      Last      : Natural       := 0;
+      Reference : not null String_Access := Null_String'Access;
+      Last      : Natural                := 0;
    end record with Put_Image => Put_Image;
 
    procedure Put_Image

[Ada] Reference in Unbounded_String is almost never null

[Pierre-Marie de Rodat]

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The underlying reference in Unbounded_String is almost never null, so
recently it was changed to a non-excluding type (to avoid runtime checks
that are almost never needed).

The low-level routines that modify that reference had to be adapted, but
only the Deallocate routine was adapted. This patch adapts the
Realloc_For_Chunk routine as well.

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

gcc/ada/

	* libgnat/a-strunb.adb (Deallocate): Rename Reference_Copy to
	Old, to make the code similar to other routines in this package.
	(Realloc_For_Chunk): Use a temporary, deallocate the previous
	string using a null-allowing copy of the string reference.

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diff --git a/gcc/ada/libgnat/a-strunb.adb b/gcc/ada/libgnat/a-strunb.adb
--- a/gcc/ada/libgnat/a-strunb.adb
+++ b/gcc/ada/libgnat/a-strunb.adb
@@ -506,11 +506,11 @@ package body Ada.Strings.Unbounded is
 
       if Object.Reference /= Null_String'Access then
          declare
-            Reference_Copy : String_Access := Object.Reference;
+            Old : String_Access := Object.Reference;
             --  The original reference cannot be null, so we must create a
             --  copy which will become null when deallocated.
          begin
-            Deallocate (Reference_Copy);
+            Deallocate (Old);
             Object.Reference := Null_Unbounded_String.Reference;
          end;
          Object.Last := 0;
@@ -833,9 +833,13 @@ package body Ada.Strings.Unbounded is
             Tmp : constant String_Access :=
               new String (1 .. New_Rounded_Up_Size);
 
+            Old : String_Access := Source.Reference;
+            --  The original reference cannot be null, so we must create a copy
+            --  which will become null when deallocated.
+
          begin
             Tmp (1 .. Source.Last) := Source.Reference (1 .. Source.Last);
-            Free (Source.Reference);
+            Free (Old);
             Source.Reference := Tmp;
          end;
       end if;