From: robert_dewar@my-dejanews.com
Subject: Re: should I be interested in ada?
Date: 1999/02/19
Date: 1999-02-19T00:00:00+00:00 [thread overview]
Message-ID: <7akted$i86$1@nnrp1.dejanews.com> (raw)
In-Reply-To: 7aknfn$au1$1@plug.news.pipex.net
In article <7aknfn$au1$1@plug.news.pipex.net>,
"Nick Roberts" <Nick.Roberts@dial.pipex.com> wrote:
> Correct for most existing Ada and Fortran compilers.
> However, I do not believe that this would be true for an
> Ada compiler which generates code
> 'late' (i.e. effectively at the linking stage).
No, this is wrong! My statement was not about compilers it
is about languages and the formal definition of when
execution is undefined (and hence what assumptions can
be made).
As surely you must know it is obviously undecidable whether
two parameters are aliased. Yes, analysis of the entire
program (of course impractical in many cases) can determine
additional aliasing information, but that has very little
to do with the observation I made, which was about formal
language definitions.
Fortran has a definite advantage here. If you do not agree,
then there is something you are missing!
> I believe there is a trend, these days, for aggressively
> optimising compilers to be of the 'late code' persuasion
> (mine will be). Of course, admittedly, even such
> compilers cannot get round the problem for the
> generation of a 'shared object' library (aka DLL).
I am not quite sure what you mean by "late code"
persuasion. If you are simply talking about delaying
code generation till link time, this is infeasible in
multi-million line programs, especially given modern
optimization algorithms which tend to be non-linear
in the size of programs. Some modest interprocedural
analysis, perhaps guided by profiling information, is
indeed practical.
> On the other hand, ironically, Fortran (77 and 90) often
> cannot perform this optimisation (reliably), since the
> language has always suffered from the fact that not all
> compilers have enforced the 'no aliasing' rule, and
> therefore many programs (unfortunately) have been written
> which take advantage of this fact.
First of all, it is of course impossible to "enforce" the
no aliasing rule, that is why it such enforcement is
neither expected nor required (it is like uninitialized
variable access in Ada).
It is quite false that compilers do not take advantage of
the aliasing rules of Fortran, they very definitely do, and
I do not know from where you would get a contrary
impression. Even Fortran-2 on the 7090 took advantage of
these rules (which were already enshrined in the Fortran
66 standard).
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next prev parent reply other threads:[~1999-02-19 0:00 UTC|newest]
Thread overview: 89+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-02-14 0:00 should I be interested in ada? Phillip Helbig
1999-02-15 0:00 ` Marin David Condic
1999-02-23 0:00 ` David Starner
1999-02-15 0:00 ` Gautier
1999-02-16 0:00 ` Ken Thomas
1999-02-17 0:00 ` Nick Roberts
1999-02-18 0:00 ` robert_dewar
1999-02-18 0:00 ` Nick Roberts
1999-02-18 0:00 ` William Clodius
1999-02-18 0:00 ` nabbasi
1999-02-18 0:00 ` robert_dewar
1999-02-18 0:00 ` robert_dewar
1999-02-19 0:00 ` William Clodius
1999-02-19 0:00 ` Nick Roberts
1999-02-20 0:00 ` robert_dewar
1999-02-22 0:00 ` Nick Roberts
1999-02-22 0:00 ` William Clodius
1999-02-23 0:00 ` robert_dewar
1999-02-23 0:00 ` Nick Roberts
1999-02-22 0:00 ` William Clodius
1999-02-23 0:00 ` Nick Roberts
1999-02-23 0:00 ` William Clodius
1999-02-25 0:00 ` Nick Roberts
1999-02-25 0:00 ` robert_dewar
1999-02-23 0:00 ` Robert I. Eachus
1999-02-24 0:00 ` Nick Roberts
1999-02-26 0:00 ` Robert A Duff
1999-02-27 0:00 ` Semantic info pragmas (was: should I be interested in ada?) Nick Roberts
1999-03-01 0:00 ` Samuel Tardieu
1999-03-01 0:00 ` Robert A Duff
1999-02-24 0:00 ` should I be interested in ada? William Clodius
1999-02-24 0:00 ` William Clodius
1999-02-25 0:00 ` Nick Roberts
1999-02-25 0:00 ` robert_dewar
1999-02-26 0:00 ` Nick Roberts
1999-02-18 0:00 ` Jerry Petrey
1999-02-18 0:00 ` fraser
1999-02-19 0:00 ` Matthew Heaney
1999-02-20 0:00 ` fraser
1999-02-18 0:00 ` Nick Roberts
1999-02-18 0:00 ` Dan Nagle
1999-02-18 0:00 ` nabbasi
1999-02-19 0:00 ` Nick Roberts
1999-02-19 0:00 ` robert_dewar
1999-02-19 0:00 ` Nick Roberts
1999-02-19 0:00 ` robert_dewar [this message]
1999-02-21 0:00 ` William Clodius
1999-02-23 0:00 ` Robert I. Eachus
1999-02-19 0:00 ` William Clodius
1999-02-20 0:00 ` Nick Roberts
1999-02-21 0:00 ` robert_dewar
1999-02-21 0:00 ` William Clodius
1999-02-22 0:00 ` Nick Roberts
1999-02-19 0:00 ` Dan Nagle
1999-02-19 0:00 ` robert_dewar
1999-02-19 0:00 ` Nick Roberts
1999-02-19 0:00 ` Dan Nagle
1999-02-23 0:00 ` Peter Hermann
1999-02-18 0:00 ` Joel Seidman
1999-02-18 0:00 ` robert_dewar
1999-02-19 0:00 ` Nick Roberts
1999-02-19 0:00 ` robert_dewar
1999-02-19 0:00 ` dennison
1999-02-19 0:00 ` Nick Roberts
1999-02-20 0:00 ` robert_dewar
1999-02-22 0:00 ` Nick Roberts
1999-02-19 0:00 ` William Clodius
1999-02-19 0:00 ` robert_dewar
1999-02-19 0:00 ` Phillip Helbig
1999-02-19 0:00 ` Nick Roberts
1999-02-20 0:00 ` robert_dewar
1999-02-20 0:00 ` Steve Doiel
1999-02-20 0:00 ` robert_dewar
1999-02-22 0:00 ` Nick Roberts
1999-02-23 0:00 ` Robert I. Eachus
1999-02-24 0:00 ` White rabbit (was: should I be interested in ada?) dennison
1999-02-25 0:00 ` Alice books " JP Thornley
1999-02-25 0:00 ` Robert I. Eachus
1999-02-22 0:00 ` should I be interested in ada? dennison
1999-02-19 0:00 ` William Clodius
1999-02-18 0:00 ` robert_dewar
1999-02-18 0:00 ` Nick Roberts
1999-02-18 0:00 ` William Clodius
1999-02-18 0:00 ` dennison
1999-02-20 0:00 ` Hartmut H. Schaefer
1999-02-20 0:00 ` bill
1999-02-21 0:00 ` dewar
1999-02-21 0:00 ` dewar
1999-02-22 0:00 ` dennison
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