[Ada] Secondary stack leak in statements block located in a loop

[Ada] Secondary stack leak in statements block located in a loop

When a loop iterator has a block declaration containing statements that invoke
functions whose result is returned on the secondary stack (such as a
string-returning function), the compiler fails to generate code to release the
allocated memory when the loop terminates.

After this patch the following test works fine.

with Ada.Text_IO; use Ada.Text_IO;
with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;
pragma Warnings (Off);
with System.Secondary_Stack;
pragma Warnings (On);

procedure Small is
   procedure Info is new System.Secondary_Stack.Ss_Info (Put_Line);

   US : Unbounded_String;
begin
   Info;
   for J in 1 .. 100_000 loop
      Leaky_Block : declare
      begin
         if (J mod 20000) = 0 then
            Info;
         end if;

         Ada.Text_IO.Put_Line (To_String (US));  --  Test

         if (J mod 20000) = 0 then
            Info;
         end if;
      end Leaky_Block;
   end loop;
   Info;
end;

Command:
  gnatmake small.adb; small | grep "Current allocated space :" | uniq
Output:
  Current allocated space :  0 bytes

2018-07-17  Javier Miranda  <miranda@adacore.com>

gcc/ada/

	* exp_ch7.adb (Make_Transient_Block): When determining whether an
	enclosing scope already handles the secondary stack, take into account
	transient blocks nested in a block that do not manage the secondary
	stack and are located within a loop.

From-SVN: r262779