[Ada] Minimal binder

The new minimal binder option ("-minimal") suppresses the generation of
binder objects that are not strictly required for program operation.
This option is suitable for space constrained applications and comes
with the restriction that programs can no longer be debugged using GDB.

2019-07-11  Patrick Bernardi  <bernardi@adacore.com>

gcc/ada/

	* bindgen.adb (Gen_Main): Do not generate a reference to
	Ada_Main_Program_Name when the Minimal_Binder flag is set.
	(Gen_Output_File_Ada): Do not output GNAT_Version and
	Ada_Main_Program_Name info if Minimal_Binder flag is set.
	* bindusg.adb: Add documentation for new -minimal switch.
	* gnatbind.adb (Scan_Bind_Arg): Scan -minimal switch.
	* opt.ads: Add new global flag Minimal_Binder to indicate if the
	binder should not produce global variables.
	* doc/gnat_ugn/building_executable_programs_with_gnat.rst:
	Update documentation with new binder -minimal switch.
	* gnat_ugn.texi: Regenerate.

From-SVN: r273401

7 files changed, 86 insertions, 17 deletions

diff --git a/gcc/ada/ChangeLog b/gcc/ada/ChangeLog
index cc3eb1d..472a6fd 100644
--- a/gcc/ada/ChangeLog
+++ b/gcc/ada/ChangeLog
@@ -1,3 +1,17 @@
+2019-07-11  Patrick Bernardi  <bernardi@adacore.com>
+
+	* bindgen.adb (Gen_Main): Do not generate a reference to
+	Ada_Main_Program_Name when the Minimal_Binder flag is set.
+	(Gen_Output_File_Ada): Do not output GNAT_Version and
+	Ada_Main_Program_Name info if Minimal_Binder flag is set.
+	* bindusg.adb: Add documentation for new -minimal switch.
+	* gnatbind.adb (Scan_Bind_Arg): Scan -minimal switch.
+	* opt.ads: Add new global flag Minimal_Binder to indicate if the
+	binder should not produce global variables.
+	* doc/gnat_ugn/building_executable_programs_with_gnat.rst:
+	Update documentation with new binder -minimal switch.
+	* gnat_ugn.texi: Regenerate.
+
 2019-07-11  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* Makefile.rtl: Add warning note about compilation flags and
diff --git a/gcc/ada/bindgen.adb b/gcc/ada/bindgen.adb
index e135540..8ea8a6b 100644
--- a/gcc/ada/bindgen.adb
+++ b/gcc/ada/bindgen.adb
@@ -1810,9 +1810,11 @@ package body Bindgen is
       --  with a pragma Volatile in order to tell the compiler to preserve
       --  this variable at any level of optimization.
 
-      --  CodePeer and CCG do not need this extra code on the other hand
+      --  CodePeer and CCG do not need this extra code. The code is also not
+      --  needed if the binder is in "Minimal Binder" mode.
 
       if Bind_Main_Program
+        and then not Minimal_Binder
         and then not CodePeer_Mode
         and then not Generate_C_Code
       then
@@ -2354,25 +2356,27 @@ package body Bindgen is
          --  program uses two Ada libraries). Also zero terminate the string
          --  so that its end can be found reliably at run time.
 
-         WBI ("");
-         WBI ("   GNAT_Version : constant String :=");
-         WBI ("                    """ & Ver_Prefix &
-                                   Gnat_Version_String &
-                                   """ & ASCII.NUL;");
-         WBI ("   pragma Export (C, GNAT_Version, ""__gnat_version"");");
+         if not Minimal_Binder then
+            WBI ("");
+            WBI ("   GNAT_Version : constant String :=");
+            WBI ("                    """ & Ver_Prefix &
+                                      Gnat_Version_String &
+                                      """ & ASCII.NUL;");
+            WBI ("   pragma Export (C, GNAT_Version, ""__gnat_version"");");
 
-         WBI ("");
-         Set_String ("   Ada_Main_Program_Name : constant String := """);
-         Get_Name_String (Units.Table (First_Unit_Entry).Uname);
+            WBI ("");
+            Set_String ("   Ada_Main_Program_Name : constant String := """);
+            Get_Name_String (Units.Table (First_Unit_Entry).Uname);
 
-         Set_Main_Program_Name;
-         Set_String (""" & ASCII.NUL;");
+            Set_Main_Program_Name;
+            Set_String (""" & ASCII.NUL;");
 
-         Write_Statement_Buffer;
+            Write_Statement_Buffer;
 
-         WBI
-           ("   pragma Export (C, Ada_Main_Program_Name, " &
-            """__gnat_ada_main_program_name"");");
+            WBI
+              ("   pragma Export (C, Ada_Main_Program_Name, " &
+               """__gnat_ada_main_program_name"");");
+         end if;
       end if;
 
       WBI ("");
diff --git a/gcc/ada/bindusg.adb b/gcc/ada/bindusg.adb
index 0207479..8331745 100644
--- a/gcc/ada/bindusg.adb
+++ b/gcc/ada/bindusg.adb
@@ -178,6 +178,12 @@ package body Bindusg is
         ("  -mnnn     Limit number of detected errors/warnings to nnn "
          & "(1-999999)");
 
+      --  Line for -minimal switch
+
+      Write_Line
+        ("  -minimal  Generate binder file suitable for space-constrained "
+         & "applications");
+
       --  Line for -M switch
 
       Write_Line
diff --git a/gcc/ada/doc/gnat_ugn/building_executable_programs_with_gnat.rst b/gcc/ada/doc/gnat_ugn/building_executable_programs_with_gnat.rst
index af8f8a4..2e867e2 100644
--- a/gcc/ada/doc/gnat_ugn/building_executable_programs_with_gnat.rst
+++ b/gcc/ada/doc/gnat_ugn/building_executable_programs_with_gnat.rst
@@ -6475,7 +6475,6 @@ be presented in subsequent sections.
   Rename generated main program from main to xyz. This option is
   supported on cross environments only.
 
-
   .. index:: -m  (gnatbind)
 
 :switch:`-m{n}`
@@ -6488,6 +6487,16 @@ be presented in subsequent sections.
   A value of zero means that no limit is enforced. The equal
   sign is optional.
 
+  .. index:: -minimal  (gnatbind)
+
+:switch:`-minimal`
+  Generate a binder file suitable for space-constrained applications. When
+  active, binder-generated objects not required for program operation are no
+  longer generated. **Warning:** this option comes with the following
+  limitations:
+
+  * Debugging will not work;
+  * Programs using GNAT.Compiler_Version will not link.
 
   .. index:: -n  (gnatbind)
 
diff --git a/gcc/ada/gnat_ugn.texi b/gcc/ada/gnat_ugn.texi
index 29424e7..e3d6a3a 100644
--- a/gcc/ada/gnat_ugn.texi
+++ b/gcc/ada/gnat_ugn.texi
@@ -15892,6 +15892,25 @@ limit, then a message is output and the bind is abandoned.
 A value of zero means that no limit is enforced. The equal
 sign is optional.
 
+@geindex -minimal (gnatbind)
+
+@item @code{-minimal}
+
+Generate a binder file suitable for space-constrained applications. When
+active, binder-generated objects not required for program operation are no
+longer generated. @strong{Warning:} this option comes with the following
+limitations:
+
+
+@itemize *
+
+@item 
+Debugging will not work;
+
+@item 
+Programs using GNAT.Compiler_Version will not link.
+@end itemize
+
 @geindex -n (gnatbind)
 
 @item @code{-n}
diff --git a/gcc/ada/gnatbind.adb b/gcc/ada/gnatbind.adb
index 40c85b9..a3b6a7e 100644
--- a/gcc/ada/gnatbind.adb
+++ b/gcc/ada/gnatbind.adb
@@ -474,6 +474,17 @@ procedure Gnatbind is
 
             Mapping_File := new String'(Argv (4 .. Argv'Last));
 
+         --  -minimal
+
+         elsif Argv (2 .. Argv'Last) = "minimal" then
+            if not Is_Cross_Compiler then
+               Write_Line
+                 ("gnatbind: -minimal not expected to be used on native " &
+                  "platforms");
+            end if;
+
+            Opt.Minimal_Binder := True;
+
          --  -Mname
 
          elsif Argv'Length >= 3 and then Argv (2) = 'M' then
diff --git a/gcc/ada/opt.ads b/gcc/ada/opt.ads
index 4c1cf6f..4d3e87e 100644
--- a/gcc/ada/opt.ads
+++ b/gcc/ada/opt.ads
@@ -1120,6 +1120,12 @@ package Opt is
    --  Maximum number of processes that should be spawned to carry out
    --  compilations.
 
+   Minimal_Binder : Boolean := False;
+   --  GNATBIND
+   --  Set to True to suppress the generation of objects by the binder that
+   --  are not strictly required for a program to run. Intended for ZFP
+   --  applications that have tight memory constraints.
+
    Minimal_Recompilation : Boolean := False;
    --  GNATMAKE
    --  Set to True if minimal recompilation mode requested