Problem
-------

        In  this  assignment we  will  learn  the  role of  Link  Time
        Optimization  (LTO). LTO combines  all compilation  units that
        make up  a single executable  and enables optimization  of the
        entire  program as  a single  unit. LTO  can only  combine the
        translation units submitted to GCC and hence library functions
        are  not   covered  by  LTO.    This  expands  the   scope  of
        interprocedural optimizations  to encompass the  whole program
        (or, rather, everything that is visible at link time).

        A  patch is  provided to  you. This  patch dumps  the  list of
        passes executed in each phase and the values of the flags. The
        value  of the  flags indicates  whether  the phase  is wpa  or
        ltrans. Makefile and the  input programs `test1.c' & `test2.c'
        are also provided.

        Place the patch alongwith the gcc-4.7.2 source directory.
        Command to apply the patch is
                patch -p0 <pass_dump_patch
        Build gcc again.
        (We have already  applied the patch and installed  the gcc for
        you. Use g++-4.7.2-lto to invoke the applied patch.)

        A dynamic plugin for  interprocedural pass is provided to you.
        This  pass iterates over  all the  functions and  prints every
        gimple  statement  in the  function.  Makefile  and the  input
        programs `test1.c' & `test2.c' are also provided.

  
        1. Use the Makefile and build the target without the option

		"-flto"

        2. Use the Makefile and build the target with the option 

		i.   "-flto -flto-partition=none"

		ii.  "-flto -flto-partition=balanced"

		iii. "-flto -flto-partition=1to1"

        3. With    the   option    -flto-partition=balanced   multiple
           partitions  can   be  created.   Use  the   option  --param
           lto-partitions  and  --param lto-min-partition  to  specify
           partitions of different sizes.

           Observe 
                - which function  bodies are  dumped in the  dump file
                  with the  extension `.dump_fns*' for  the individual
                  test programs.

                - which function  bodies are dumped after  merging the
                  .o files in both the wpa and ltrans phase.

                - the values of flags displayed on the terminal.

          a.  What difference  do you  observe with and  without -flto
              option?

          b.  What  difference  do  you  observe  with  the  different
              -flto-partition options?

          c.  Can you construct multiple partitions of different sizes
              using  the  option  --param lto-partitions  and  --param
              lto-min-partition?

Procedure
---------
Note : Type command `make clean' before every use of `make'.

        The  following steps are to be followed to  execute the  given
        pass. The  Makefile uses  the name  `merged' for  the combined
        translation unit.

        1.  Execute the plugin  by giving the command `make test'. The
            option "-flto" has not been specified for this target.

        2.  Read    the    dump     files    with    the    extensions
            `.dump-fns-after-pta'  and   `.dump-fns-after-inline'  for
            individual  test   files.  Do  you  find   a  file  called
            `merged.*.dump-fns*'? What is the value of flag `in_lto_p'
            and why?

        3.  Execute   the  plugin   by   giving   the  command   `make
            test-none'.  The option  used  for this  target is  "-flto
            -flto-partition=none". When  is the value of  the flag _p'
            `in_ltoset  to 1  and  why?  What are  the  values of  the
            flag_wpa' and flags ``flag_ltrans'? What do they indicate?

        4.  Read  the  dump  files with  the  extensions  `.dump-fns*'
            for   individual   test   files    and   also   the   file
            `merged.*.dump-fns*'. Observe the values of all the flags.

        5.  Execute   the  plugin   by   giving   the  command   `make
            test-balanced'. The option that is used for this target is
            "-flto -flto-partition=balanced". 

        6.  Read  the  dump  files with  the  extensions  `.dump-fns*'
            for   individual   test   files    and   also   the   file
            `merged.*.dump-fns*'. Observe the values of all the flags.
            Why  is  the  function   `lto_main'  called  twice?  Flags
            `flag_wpa' and  `flag_ltrans' can have values  either 0 or
            1. When wpa and ltrans phase  is invoked what is the value
            of these flags?

        7.  Execute the plugin by giving the command `make test-1to1'.
            The  option  that  is  used  for  this  target  is  "-flto
            -flto-partition=1to1".

        8.  Read  the  dump  files with  the  extensions  `.dump-fns*'
            for   individual   test   files    and   also   the   file
            `merged.*.dump-fns*'. Observe the values of all the flags.
            Why  do  we have  multiple  `ltrans'  phase? How  are  the
            partitions formed?

        9.  Execute   the  plugin   by   giving   the  command   `make
            test-balanced1' & `make test-balanced2'.

        10. Observe  the difference  in the  output and  explain. Also
            observe  the values  of  all  the flags.  Why  is there  a
            difference in the number of times `lto_main' being called?
            The number of  partitions formed is different  in both the
            cases. Why is there a difference in the partitions formed?