Re: Source Analysis Tools for Ada95

[Simon Wright <simon@pushface.org>]

tony@probepak.com (Dr. Anthony Probe) writes:

> > Gnat includes "gnatelim" which generates a list of gnat specific
> > pragmas causing no object code to be built for dead code.  You
> > should be able to use this as a starting point for deleting unused
> > code.
> 
> Wouldn't a compiler only detect the obvious dead code (that which
> isn't used from just analyzing the comp unit?

I have never used gnatelim, because the one time I tried it took a
long time (this was a few years ago) and I didn't really have a
problem anyway. But its intention is to find and mark those
subprograms (?and other constructs?) that aren't used in the
closure. Sounds like what you're after!

You need to get the binary distribution, because gnatelim isn't built
as part of the compiler (I believe it's an ASIS application).

Quotation from the 3.14p GNAT user's guide:

   When a program shares a set of Ada packages with other programs, it
   may happen that this program uses only a fraction of the
   subprograms defined in these packages. The code created for these
   unused subprograms increases the size of the executable.

   gnatelim tracks unused subprograms in an Ada program and outputs a
   list of GNAT-specific Eliminate pragmas (see next section) marking
   all the subprograms that are declared but never called. By placing
   the list of Eliminate pragmas in the GNAT configuration file
   `gnat.adc' and recompiling your program, you may decrease the size
   of its executable, because the compiler will not generate the code
   for 'eliminated' subprograms.

   The simplified syntax of the Eliminate pragma used by gnatelim is:

   pragma Eliminate (Library_Unit_Name, Subprogram_Name);

   where

   Library_Unit_Name
      full expanded Ada name of a library unit
   
   Subprogram_Name
      a simple or expanded name of a subprogram declared within this
      compilation unit


Also, -gnatwu will warn of unused entities, including withed units. I
think this is GNAT 3.15p or later. (we use -gnatwaL, switch on all
warnings except elaboration ordering).