Re: Crosspost: Help wanted from comp.compilers

["Robert I. Eachus" <rieachus@attbi.com>]

Hyman Rosen wrote:

> Here's some evidence. I have no idea about its quality.
> Given the unfortunate lack of a worldwide web in the 80s,
> it's not clear where to search for more data. Looking at
> some of the links below, I think a big problem was that
> many of the systems forced all dependents of a file to be
> recompiled when the file was recompiled, regardless of
> whether the source had changed.

If you understood Ada, you would understand that all of the "evidence" 
you supplied confirmes what we have said.  The issue going into the Ada 
9X process was that tools that tried to short-cut the Ada recompilation 
rules were tried--and they were much worse than the problem.

>                                   I believe this was one
> reason that GNAT decided to go with a source-based model
> for its library.

Hoo, boy.  That is good.  Do you really understand how the GNAT "source 
based" model works?  Everytime you compile a unit the specification for 
  every package/unit withed by that unit is recompiled.  Every time you 
modify a subunit the library unit, or a library unit with subunits, the 
library unit and all of its subunits needs to be recompiled.  In other 
words, the GNAT model does lots more recompilation, not less.  The 
benefit is that the overhead of compiling specifications is kept very 
low, so the recompilation from source is faster than saving an 
intermediate state and restoring it.

-- 

                                                        Robert I. Eachus

�In an ally, considerations of house, clan, planet, race are 
insignificant beside two prime questions, which are: 1. Can he shoot? 2. 
Will he aim at your enemy?� -- from the Laiden novels by Sharon Lee and 
Steve Miller.