[Ada] More complete information level for -gnatR output

[Ada] More complete information level for -gnatR output

This adds a 4th information level for the -gnatR output, where relevant
compiler-generated types are listed in addition to the information
already output by -gnatR3.

For the following package P:

package P is

  type Arr0 is array (Positive range <>) of Boolean;

    type Rec (D1 : Positive; D2 : Boolean) is record
       C1 : Integer;
       C2 : Arr0 (1 .. D1);

       case D2 is
          when False =>
             C3 : Character;
          when True =>
             C4 : String (1 .. 3);
             C5 : Float;
       end case;
    end record;

    type Arr1 is array (1 .. 8) of Rec (1, True);

end P;

the output generated by -gnatR4 must be:

Representation information for unit P (spec)
--------------------------------------------

for Arr0'Alignment use 1;
for Arr0'Component_Size use 8;

for Rec'Object_Size use 17179869344;
for Rec'Value_Size use (if (#2 != 0) then ((((#1 + 15) & -4) + 8) * 8)
else ((((#1 + 15) & -4) + 1) * 8) end);
for Rec'Alignment use 4;
for Rec use record
   D1 at  0 range  0 .. 31;
   D2 at  4 range  0 ..  7;
   C1 at  8 range  0 .. 31;
   C2 at 12 range  0 .. ((#1 * 8)) - 1;
   C3 at ((#1 + 15) & -4) range  0 ..  7;
   C4 at ((#1 + 15) & -4) range  0 .. 23;
   C5 at (((#1 + 15) & -4) + 4) range  0 .. 31;
end record;

for Arr1'Size use 1536;
for Arr1'Alignment use 4;
for Arr1'Component_Size use 192;

for Tarr1c'Size use 192;
for Tarr1c'Alignment use 4;
for Tarr1c use record
   D1 at  0 range  0 .. 31;
   D2 at  4 range  0 ..  7;
   C1 at  8 range  0 .. 31;
   C2 at 12 range  0 ..  7;
   C4 at 16 range  0 .. 23;
   C5 at 20 range  0 .. 31;
end record;

2018-11-14  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* doc/gnat_ugn/building_executable_programs_with_gnat.rst
	(-gnatR): Document new -gnatR4 level.
	* gnat_ugn.texi: Regenerate.
	* opt.ads (List_Representation_Info): Bump upper bound to 4.
	* repinfo.adb: Add with clause for GNAT.HTable.
	(Relevant_Entities_Size): New constant.
	(Entity_Header_Num): New type.
	(Entity_Hash): New function.
	(Relevant_Entities): New set implemented with GNAT.HTable.
	(List_Entities): Also list compiled-generated entities present
	in the Relevant_Entities set. Consider that the Component_Type
	of an array type is relevant.
	(List_Rep_Info): Reset Relevant_Entities for each unit.
	* switch-c.adb (Scan_Front_End_Switches): Add support for -gnatR4.
	* switch-m.adb (Normalize_Compiler_Switches): Likewise
	* usage.adb (Usage): Likewise.

From-SVN: r266131