Re: Ada to C/C++ translator needed

[Erik Magnuson <erik@fl.ensco.com>]

dewar@schonberg.cs.nyu.edu (Robert Dewar) writes:

> 
> Frank said
> 
> "Awhile back there was a big discussion about the merits of writing an
> 8051 Ada compiler. I'm a bit surprised nobody mentioned this
> possibility, since 8051 C compilers already exist."
> 
> If you think that the existence of an Ada 83 compiler that generates C 
> means that there is an easy path to an acceptably efficient Ada compiler
> on any machine with a C compiler, you are seriously fooling yourself for
> all sorts of reasons. Nothing is as straightforward as one might hope!
> 

In a former life, I used to use such a beast daily and quickly came to
realize just why this is not a favored path to what we would call a
"production quality compiler". (No offense to the vendor intended, it was
impressive that it worked as well as it did.)

Realize that if you want to get decent performance even writing low-level C
these days you have to enable the C compiler's optimizer. You can imagine
what contortions the code generator has to go through to make sure the C
optimizer does not hose the Ada semantics.  Not to mention to workaround the
bugs in said optimizer (which change in every release.)  Especially since
the C compiler vendor's test suite is very unlikely to contain such odd
code. (Imagine reporting such bugs to the C vendor: "You're doing what?!").

And think about how much fun debugging becomes. For if you have no Ada code
generator, you're not likely to have an Ada debugger!  Oh, the joy of trying
to make sense of 3 listings (the Ada source, the generated C and the
generated assembler.)  It was not pretty. Supporting nested
procedures was a particular joy to behold.  

In addition, I believe that 8051 C compilers tend to have extensions to
exploit the features of the chip. You'll want these of course. You'll have
lots of fun trying to decide how to map onto these. 

And the compilation speed will be at least twice as bad as the C
compiler. Think about it: you have at least the entire C compiler overhead
as well as your Ada compiler source -> code gen (including the Ada
compiler's highlevel optimizer.)  (For this example, imagine the C compiler
is a hasty port of a Unix compiler to VMS that does lot's unixy things that
VMS just hates, like spawning many processes that communicate via temp files
that are byte streams, etc.) 

-- 
Erik Magnuson, ENSCO	erik@fl.ensco.com
MARSS-REPL  		(407) 783-7114