Re: naval systems

[David Starner <dvdeug@x8b4e53cd.dhcp.okstate.edu>]

On Wed, 27 Feb 2002 21:44:32 GMT, Pat Rogers <progers@classwide.com> wrote:
> Ah, this is what I'm trying to get to.  Taking the defaults for the two
> compilers/languages is *not* comparable.  You need to at least turn of run-time
> checking for the Ada program.  That's enough to invalidate the test by itself.
> 
>> Given both the null program and Hello, World!, the C compiler took about
>> 1/3 of the time that GNAT did, with no options and with -O2 -g.
> 
> That isn't as meaningful as one might think, although it is not an uncommon
> test.  I assume you used Text_IO?  The compile times were hugely overshadowed by
> handling of the I/O libraries.  That is not a comparable program to one in C
> that uses the much simpler I/O library.
> 
>> I generated a 32,002 line program that had 32,000 randomly pointing (but
>> the same for the C and Ada program) goto statements in it, and told it
>> to write to assembly only, with no optimization. The C compiler took 4
>> seconds. GNAT took 7 minutes to tell me I was missing a semicolon. After
>> fixing that semicolon, it took 6 minutes 59 seconds to produce assembly
>> with no significant difference.
>>
>> The last case is a bit pathological, but it is a data point.
> 
> So pathological, in fact, that I don't believe they were the "same" program.
> I'm surprised anyone would!

You mean, besides the fact that GNAT and GNU C produced the exact same
assembly, except for four instructions (apparently GNU C felt the need
to align the stack, where GNAT didn't). You mean besides the fact the
fact the two programs have the exact same semantics - emit no output and
never exit except on a signal.
 
> It is extremely easy to get this kind of thing wrong -- thinking that the
> semantics are the same when they aren't.  I've done it before and no doubt will
> do it again.  It is trivially easy to drive an Ada compiler to its knees -- over
> a period of several grinding minutes in some compilers -- by declaring a series
> of named numbers that look like regular old C constants.

All nice advocate answers. Now back to real life, if I write several
programs simple enough that the semantics are exactly the same for each
language, and each one is slower to compile with GNAT than GNU C, then
I will come to the conclusion that GNAT is slower than GNU C.

You seem to be interested in some idealized "fair" compairson. But
that's not what matters - what matters is how long it takes on real life
programs.
 
> Otherwise we are
> only comparing implementations and cannot generalize the result.

Um, of course we can generalize the result. That's science - you take
sample data points and see if you can draw a conclusion. How an
idealized optimal Ada compiler performs is of little interest; how the
Ada compiler that's on their desk or will be on their desk performs is
of interest.

> Again, we are talking about compile time, not the time it takes to build the
> executable, because indeed the Ada binder/linker implements requirements that
> the C tools do not bother with, like interface consistency.  And again, we are
> talking about compiling the same way -- with the switches set so that the
> compilers behave comparably.  Turning of the checking is the obvious example.

You keep trying to add a handicap. The interesting question is time from
submitting the sources to getting a binary; any features is a whole
different question. What switches should be added is a complex question,
but the answer should have to do with what will be normally used, and
not what would make it more theoratically "fair".

> At the end of the day, we are in agreement that in practice the time it takes to
> produce an executable image from an Ada toolchain is typically slightly longer.
> What we're arguing is whether the compilation phase itself is inherently slower,

What does "inherently slower" mean? If you go back to the original post
to which I responded, he was talking about most implementations being as
fast as most C implementations; that was what I was responding to; I
never said anything about all Ada implementations being inherently slower.

-- 
David Starner - starner@okstate.edu
What we've got is a blue-light special on truth. It's the hottest thing 
with the youth. -- Information Society, "Peace and Love, Inc."