Re: Crosspost: Help wanted from comp.compilers

[Richard Riehle <richard@adaworks.com>]

tmoran@acm.org wrote:

>
>   Remember that Ada has separate specs and bodies.  If you want to change
> the optimization or get additional debug output on the body, you can
> recompile the body and it doesn't cause cascades.  If you recompile the
> spec with a different optimization level then some things (record layouts,
> for instance) might change, and you certainly had better recompile
> anything that depends on that spec.

I recall one of oiur Ada 83 clients who developed a large system for the
DoD and constantly complained about how long it took to compile
programs.  We looked at the dependencies early in our review and
discovered that nearly context clause was at the package specification
level even though much of the stuff did not require context clauses
at that level.  The compiler they were using did not issue a warning about
this.

In many cases,  simply moving the context clauses to the body was
sufficient.  In other cases, slight changes were necessary to the
specification   to  permit moving context clauses.  In a few cases,
it was appropriate to declare "is separate"  for certain subprograms
in the body and move the dependencies to the separately compiled
subunits.

This solution greatly improved compilation times, made maintenance
much more convenient, and reduced some of the overhead spent on
programmers who needed to stay on into the night watching their
compilations grind on, while they watched in the hope the  computer
would not crash (it sometimes did) during recompilation.

Even with Ada 83, much of the complaining about long compilation
times was easily solved by designing the dependencies intelligently.
This is one benefit of the Ada separate compilation model.  Even
though many Ada practitioners dislike subunits, they did then and
continue today, to have a place in  good design.

Richard Riehle