Pragma Inline and its Effects of Compilation Dependencies.

Pragma Inline and its Effects of Compilation Dependencies.

[Ralph Corderoy]

Hi,

I was recently asked to look into an Ada compilation problem that
centred around the use of pragma inline.  The result was a realisation
that the pragmas weren't accurately reflected in the compiler suite's
dependency graph used to determine compilation order.  Consequently,
when building a set of source from scratch a separate containing an
inlined routine wasn't being built before its callers.

I'd like to check that I understand what's wrong and how it should work,
and then ask for advice on where to go from here.

Assume we've two packages, foo and bar, with bar making use of foo.

    ==> foo.s.ada <==
    package foo is
        procedure x;

        procedure y;
        pragma inline(y);
    end;

    ==> foo.b.ada <==
    package body foo is
        procedure x is separate;
        procedure y is separate;
    end;

    ==> foo.x.ada <==
    separate(foo)
    procedure x is begin null; end;

    ==> foo.y.ada <==
    separate(foo)
    procedure y is begin null; end;

    ==> bar.s.ada <==
    with foo;

    package bar is
        procedure x;
        procedure y;
    end;

    ==> bar.b.ada <==
    package body bar is
        procedure x is separate;
        procedure y is separate;
    end;

    ==> bar.x.ada <==
    separate(bar)
    procedure x is begin foo.y; end;

    ==> bar.y.ada <==
    separate(bar)
    procedure y is begin null; end;

Are these the dependencies that exist.

    1 foo.b.ada -> foo.s.ada because a body depends on its spec
    2 foo.x.ada -> foo.b.ada because a sub-unit depends on its parent
    3 foo.y.ada -> foo.b.ada because a sub-unit depends on its parent

    4 bar.b.ada -> bar.s.ada because a body depends on its spec
    5 bar.x.ada -> bar.b.ada because a sub-unit depends on its parent
    6 bar.y.ada -> bar.b.ada because a sub-unit depends on its parent

    7 bar.s.ada -> foo.s.ada because bar's spec withs foo
    8 bar.x.ada -> foo.y.ada because bar.x calls inlined foo.y

A linear ordering of this partial order is

    foo.s.ada foo.b.ada foo.x.ada foo.y.ada
    bar.s.ada bar.b.ada bar.x.ada bar.y.ada

The compiler suite I was using had instead

    8 bar.x.ada -> foo.b.ada

allowing it to use the linear ordering

    foo.s.ada foo.b.ada
    bar.s.ada bar.b.ada bar.x.ada bar.y.ada
    foo.x.ada foo.y.ada

This fails to inline foo.y because it isn't available when bar.x is
built.

I believe calling an inlined routine creates a dependency from the
caller to the routine itself, and if it is a separate that isn't the
same as the body of the package, as used by the compiler above.

First question.  How well do other compilers handle this;  not too well
judging by the the existence of adamakegen
(http://www.ics.uci.edu/~softtest/adamakegen.html) and its complaints
about Verdix/SunAda.

I've read a little about gnat's gnatmake and how the compiler doesn't
follow the normal library implementation and instead uses the source
files coupled with ALI files.  Does that mean in practice it copes
correctly with inline dependencies, including when they're in separates?
The manual seemed to suggest it didn't consider source outside the
current library.  That wouldn't help in my case.  Consider if foo was
being built into a separate Ada library from bar;  I alter foo.y.ada and
build locally there.  I then want to move to bar's library and find it
is out of date.

It seems what I need is something that will take many source files,
parse them, and spit out the dependencies for use in something like a
traditional makefile.  It isn't a trivial task as things like package
renames and use clauses help to obscure what is being called.  Plus it
mustn't make the mistake of thinking an inline creates a dependency to
the package body when a separate exists.  Does something like this
exist?

The alternative seems to be to re-build bar from scratch whenever foo is
changed because it can't be left to the compiler to calculate what to
rebuild and relying on the programmer to know who calls foo.y is a
no-no.  But building bar and everything else could take eons.

This can't be an original problem.  What do people with large Ada
projects do?


Ralph.

Re: Pragma Inline and its Effects of Compilation Dependencies.

[Robert Dewar]

In article <8b64ul$jov$1@inputplus.demon.co.uk>,
  ralph@inputplus.demon.co.uk (Ralph Corderoy) wrote:

> I was recently asked to look into an Ada compilation problem
> that centred around the use of pragma inline.  The result was
> a realisation that the pragmas weren't accurately reflected in
> the compiler suite's dependency graph used to determine
> compilation order.  Consequently, when building a set of
> source from scratch a separate containing an
> inlined routine wasn't being built before its callers.
>
> I'd like to check that I understand what's wrong and how it
> should work, and then ask for advice on where to go from here.

Your Ada compiler is being unfriendly, but not inaccurate, i.e.
the reference manual certainly permits the behavior you see. It
is quite legitimate for a compiler to fail to inline something
because the right body has not been compiled yet. The use of
pragma Inline does create additional dependencies *if* the
procedure is inlined, but there is no guarantee that the
inlining will occur.

In systems where compilation order is important (unlike GNAT
where this issue does not arise), the user is responsible for
manually choosing the order of compilation that optimizes the
use of inlining.

Consider the following:

  package x is
     procedure xx ...
     pragma Inline (xx);
     ...
  end x;

  with y;
  package body x is
      ...
      y.yy;
  end x;

  package y is
     procedure yy ...
     pragma Inline (yy);
     ...
  end y;

  with x;
  package body y is
     ...
     x.xx;
  end y;

Now in a compiler with a conventional Ada 83 style library,
the rule is that you can only inline the call y.yy if the
body of y is compiled before the body of x, and you can
only inline the call x.xx if the body of x is compiled before
the body of y.

Since both of those cannot be true, only one of these calls
can be inlined. The additional dependency will be created for
the one that is inlined, assuring consistency, but one of the
inlines will not happen.

The only way to avoid this if you have a conventional Ada 83
style library is to do inlining at the binder stage, but this
is quite expensive (I think the old Telesoft compiler did this).
Certainly the old Alsys compiler had the behavior described
above.

This often causes surprises, and means that order of compilation
is crucial in such systems and must be worked out very
carefully. Obviously no tool can do a fully automatic job, since
in the above example, both requirements cannot be met, and it
requires intervention to specify which of the two inlinings is
more important.

One of the big advantages of the source based model used first
by GNAT, and later by some (but not all) other Ada 95 compilers
is that inlining can be done accurately. In the case of GNAT
for example, the use of gnatmake with the -gnatn switch to turn
on inlining will guarantee that ALL specified inlining is
properly processed, and as usual the order of compilation is
completely irrelevant (both inlinings will be handled properly
in the above example regardless of the order of compilation).
In GNAT, it is an absolute guarantee that the order in which
compilations are done has no effect whatever on the generated
code.

Robert Dewar
Ada Core Technologies


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Re: Pragma Inline and its Effects of Compilation Dependencies.

[Paul Graham]

Robert Dewar wrote:

> One of the big advantages of the source based model used first
> by GNAT, and later by some (but not all) other Ada 95 compilers
> is that inlining can be done accurately.

Makes you wonder why the library-based method of compilation was used in
the
first place.  Perhaps the intent was to save compilation time by not
recompiling
package sources each time they are USEd in another unit.

Paul

Re: Pragma Inline and its Effects of Compilation Dependencies.

[Samuel T. Harris]

Ralph Corderoy wrote:
> 
> Hi,
> 
> I was recently asked to look into an Ada compilation problem that
> centred around the use of pragma inline.  The result was a realisation
> that the pragmas weren't accurately reflected in the compiler suite's
> dependency graph used to determine compilation order.  Consequently,
> when building a set of source from scratch a separate containing an
> inlined routine wasn't being built before its callers.
> 
> I'd like to check that I understand what's wrong and how it should work,
> and then ask for advice on where to go from here.
> 
< <snip>
> 
> I believe calling an inlined routine creates a dependency from the
> caller to the routine itself, and if it is a separate that isn't the
> same as the body of the package, as used by the compiler above.
> 
> First question.  How well do other compilers handle this;  not too well
> judging by the the existence of adamakegen
> (http://www.ics.uci.edu/~softtest/adamakegen.html) and its complaints
> about Verdix/SunAda.

In my experience I observed the following results ...

Alsys ala version 4: Usually worked, sometimes didn't.
VADS ala version 4-6: Never works well.
Rational R1000 and Apex: Always works except when mutual inlining is
involved.

This is a good area for ASIS based tools. I use just such a beast
to help resolve this issue. On the other hand, I have also found
that compilation orders which general place bodies as soon as
possible rarely have this problem so building a tool to handle
this case may not be worth while if your tool can do bodies ASAP.

If I remember correctly, Alsys had a switch to control when
bodies appear in the order. It could do as soon as possible
or as late as possible.

Note that when a compiler requires a generic body be compiled
before it is instantiated, then you have the same basic requirements.

> 
> I've read a little about gnat's gnatmake and how the compiler doesn't
> follow the normal library implementation and instead uses the source
> files coupled with ALI files.  Does that mean in practice it copes
> correctly with inline dependencies, including when they're in separates?
> The manual seemed to suggest it didn't consider source outside the
> current library.  That wouldn't help in my case.  Consider if foo was
> being built into a separate Ada library from bar;  I alter foo.y.ada and
> build locally there.  I then want to move to bar's library and find it
> is out of date.
> 
> It seems what I need is something that will take many source files,
> parse them, and spit out the dependencies for use in something like a
> traditional makefile.  It isn't a trivial task as things like package
> renames and use clauses help to obscure what is being called.  Plus it
> mustn't make the mistake of thinking an inline creates a dependency to
> the package body when a separate exists.  Does something like this
> exist?

This is easily written using ASIS queries. Lacking access to ASIS,
one can get a yacc/lex grammars for Ada and do the extra work
yourself. Hopefully, your compiler tool can spit out "normal"
dependencies so you don't have to worry about context clauses.
You only have to worry about which subprograms are inlines and
where they are called. Using syntax processes will easily handle
straight subprogram calls but requires more work if your code
is using rename declarations.

> 
> The alternative seems to be to re-build bar from scratch whenever foo is
> changed because it can't be left to the compiler to calculate what to
> rebuild and relying on the programmer to know who calls foo.y is a
> no-no.  But building bar and everything else could take eons.

If your code is stable and your dependencies are not changing
much, then you should capture the dependencies once and use that
to determine the scope of recompilation. Even if you have to visually
inspect for inline calls, you only need capture this once. Using VADS,
you can use pragma inline_only and the compiler will complain
when it can't inline the call. This feedback is crucial to maintaining
your dependency information when you capture it manually.

> 
> This can't be an original problem.  What do people with large Ada
> projects do?

Such things are important to your compiler selection.
If you need to change compilers in the future, support for this
problem area needs to be on your list. In any event, you use
what the compiler will give you and build anything else you need
to the degree that it is worth building.


> 
> Ralph.

-- 
Samuel T. Harris, Principal Engineer
Raytheon, Aerospace Engineering Services
"If you can make it, We can fake it!"

Re: Pragma Inline and its Effects of Compilation Dependencies.

[Gautier]

> > One of the big advantages of the source based model used first
> > by GNAT, and later by some (but not all) other Ada 95 compilers
> > is that inlining can be done accurately.

Paul Graham wrote:

> Makes you wonder why the library-based method of compilation was used in
> the first place.  Perhaps the intent was to save compilation time by not
> recompiling package sources each time they are USEd in another unit.

This feature doesn't force the library model in the classical Ada83 way.
E.g. Turbo Pascal and successors/clones. Or maybe the "other" Ada95 compilers ?
And it doesn't prevent accurate inlining if compiled specification holds
rich enough information (e.g. from where to pick the procedure to inline
in the source of package body, or some representation of it ?)
______________________________________________________
Gautier  --  http://members.xoom.com/gdemont/gsoft.htm

Re: Pragma Inline and its Effects of Compilation Dependencies.

[Robert Dewar]

In article <38D7F4D8.1AE44625@maths.unine.ch>,
  Gautier <gautier.demontmollin@maths.unine.ch> wrote:
> This feature doesn't force the library model in the classical
Ada83 way.
> E.g. Turbo Pascal and successors/clones. Or maybe the "other"
Ada95 compilers ?
> And it doesn't prevent accurate inlining if compiled
specification holds
> rich enough information (e.g. from where to pick the procedure
to inline
> in the source of package body, or some representation of it ?)


You miss the point. The Ada 83 library approach is based on the
idea that a compilation NEVER accesses anything that has not
been previously compiled. That is quite fundamental to the
model. If you are talking about looking at sources of things
that have not been compiled yet, then you are talking about
the other model (the source based model).

Once again, to be clear, the classical Ada 83 model has a
compilation process that is

    library  x  single-source  ---------->  updated library
                                 compile

The source based model has a quite different compilation
process that looks like

    all-other-sources x one identified source ------->  object
                                               compile

Further details are in the existing literature. As I said
earlier, the only way to do full inlining with the classical
library model is to delay inlining until binding, which is
a very heavy burden, since it means delaying much or even all
code generation till bind time.

Robert Dewar
Ada Core Technologies


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Re: Pragma Inline and its Effects of Compilation Dependencies.

[Robert Dewar]

In article <8b64ul$jov$1@inputplus.demon.co.uk>,
  ralph@inputplus.demon.co.uk (Ralph Corderoy) wrote:

> I've read a little about gnat's gnatmake and how the compiler
> doesn't follow the normal library implementation and instead
> uses the source files coupled with ALI files.

No, the compiler does NOT use ALI files, it only uses source
files. This is extremely crucial, since the set of ALI files
would be affected by the order of compilation.

> Does that mean in practice it copes
> correctly with inline dependencies, including when they're in
separates?

Yes, inlines are handled in all cases, separates make no
difference to this at all.

> The manual seemed to suggest it didn't consider source outside
> the current library.

That's confused, GNAT has no notion of library in that sense.
The only requirement is that all sources be available to the
compilation process.

> That wouldn't help in my case.  Consider if foo was
> being built into a separate Ada library from bar;  I alter
foo.y.ada and
> build locally there.  I then want to move to bar's library and
find it
> is out of date.

This kind of scenario is handled in complete generality by
gnatmake and related tools, and the correct minimal set of
sources is always identified correctly and compiled, regardless
of changing dependences.

Robert Dewar
Ada Core Technologies


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Re: Pragma Inline and its Effects of Compilation Dependencies.

[Ken Garlington]

I think the use of the library-based approach was due to a combination of
things:

- Vendors reading RM83 section 10.4 too closely: "a library file containing
information on the compilation units of the program library must be
maintained by the compiler..."

- Assumptions about efficiency.

- The desire to do things like distribute pre-compiled component sets
without releasing the source code. The presumption was that this was better
than just releasing object code, since there would be additional information
for optimizations, support tools, etc.

"Paul Graham" <pgraham@cadence.com> wrote in message
news:38D7CABA.A73F88C6@cadence.com...
> Robert Dewar wrote:
>
> > One of the big advantages of the source based model used first
> > by GNAT, and later by some (but not all) other Ada 95 compilers
> > is that inlining can be done accurately.
>
> Makes you wonder why the library-based method of compilation was used in
> the
> first place.  Perhaps the intent was to save compilation time by not
> recompiling
> package sources each time they are USEd in another unit.
>
> Paul

Re: Pragma Inline and its Effects of Compilation Dependencies.

[Larry Kilgallen]

In article <8b94tg$9jt$1@nnrp1.deja.com>, Robert Dewar <dewar@gnat.com> writes:

> You miss the point. The Ada 83 library approach is based on the
> idea that a compilation NEVER accesses anything that has not
> been previously compiled. That is quite fundamental to the
> model. If you are talking about looking at sources of things
> that have not been compiled yet, then you are talking about
> the other model (the source based model).
> 
> Once again, to be clear, the classical Ada 83 model has a
> compilation process that is
> 
>     library  x  single-source  ---------->  updated library
>                                  compile
> 
> The source based model has a quite different compilation
> process that looks like
> 
>     all-other-sources x one identified source ------->  object
>                                                compile

How would you classify a mechanism like the DEC Ada command
ACS LOAD ?  From my perspective as a user it takes away any
need for me to worry about the order of compilation even on
a clean build to an empty library.

Certainly the fact that it looks at all the sources takes
more time, but my general experience is that there are only
two categories of compilation durations:

	short enough that I will sit and wait

	long enough that I will go do something else

Larry Kilgallen

Re: Pragma Inline and its Effects of Compilation Dependencies.

[Ted Dennison]

In article <2000Mar22.085654.1@eisner>,
Kilgallen@eisner.decus.org.nospam wrote:
> In article <8b94tg$9jt$1@nnrp1.deja.com>, Robert Dewar
<dewar@gnat.com> writes:
>
> > You miss the point. The Ada 83 library approach is based on the
> > idea that a compilation NEVER accesses anything that has not
> > been previously compiled. That is quite fundamental to the

> How would you classify a mechanism like the DEC Ada command
> ACS LOAD ? From my perspective as a user it takes away any
> need for me to worry about the order of compilation even on
> a clean build to an empty library.

Its been a while (almost a decade). But as I recall, that command only
built up a list of units along with a mapping to their sources. As it
did not actually compile anything, it would not be considered a
"compilation" in the discussion above.

Just about every library-based model provides a way to introduce units
to the library without compiling them first. But in this state they are
indeed not compiled at all, so I don't think it affects the discussion
about inlining.

--
T.E.D.
http://www.telepath.com/~dennison/Ted/TED.html


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Re: Pragma Inline and its Effects of Compilation Dependencies.

[Robert Dewar]

In article <2000Mar22.085654.1@eisner>,
  Kilgallen@eisner.decus.org.nospam wrote:
> How would you classify a mechanism like the DEC Ada command
> ACS LOAD ?  From my perspective as a user it takes away any
> need for me to worry about the order of compilation even on
> a clean build to an empty library.

This is a separate utility that determines what needs compiling,
and of course all Ada systems have such tools, and that is
true for both models.

BUT, and this is a big but, and what this thread is all about,
whether inlining takes place will typically depend on the order
of compilation, and tools like ACS LOAD

a) often don't take inlining into account

b) often can't take inlining into account in the sense that they
cannot deal with mutual inlining, because there is no realiable
order in such cases. In this situation the tool cannot make the
"right" choice, and at best tells you the problem, at worst
(and most typically) steams ahead and makes an arbitrary choice
without telling you.

It may take away your worry, but that does not mean there is
nothing to worry about.

I do not know for sure what the DEC Ada 83 approach to inlining
is but it would surprise me if it did inlining at bind time.



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Re: Pragma Inline and its Effects of Compilation Dependencies.

[Wes Groleau]

> .... the only way to do full inlining with the classical
> library model is to delay inlining until binding, which is
> a very heavy burden, since it means delaying much or even all
> code generation till bind time.

I don't quite follow.  If object code has been generated within 
file xx.o for function XX.Func, what prevents a code generator,
when it reaches 

   Rec.Field := XX.Func (P, Q);

from streamlining the preamble and parameter setup and result 
assignment, and copying the rest of the object code as is.

Or do you mean something else by "full" inlining?

-- 
Wes Groleau
http://freepages.genealogy.rootsweb.com/~wgroleau

Re: Pragma Inline and its Effects of Compilation Dependencies.

[Robert A Duff]

Wes Groleau <wwgrol@ftw.rsc.raytheon.com> writes:

> I don't quite follow.  If object code has been generated within 
> file xx.o for function XX.Func, what prevents a code generator,
> when it reaches 
> 
>    Rec.Field := XX.Func (P, Q);
> 
> from streamlining the preamble and parameter setup and result 
> assignment, and copying the rest of the object code as is.

Inlining is generally not done at the object code level, but at the
level of some intermediate language that is higher level than machine
code.  The point is not just to save the call and return instructions,
but to optimize the inlined code based on information at the call site.

Eg:

    function F(X: Color) return String is
    begin
        case X is
            when Red => return "This";
            when Green => return "That";
            ...
        end case;
    end F;
    
Then if you inline a call like "F(Red)", the entire thing boils down to
a compile-time-known value.

- Bob

Re: Pragma Inline and its Effects of Compilation Dependencies.

[Larry Kilgallen]

In article <8bat53$6qb$1@nnrp1.deja.com>, Robert Dewar <robert_dewar@my-deja.com> writes:

> I do not know for sure what the DEC Ada 83 approach to inlining
> is but it would surprise me if it did inlining at bind time.

I know the capabilities of the VMS Linker, and they do not include
anything elaborate enough to do inlining.

Re: Pragma Inline and its Effects of Compilation Dependencies.

[Ralph Corderoy]

Hi Robert,

> > I was recently asked to look into an Ada compilation problem that
> > centred around the use of pragma inline.  The result was a
> > realisation that the pragmas weren't accurately reflected in the
> > compiler suite's dependency graph used to determine compilation
> > order.  Consequently, when building a set of source from scratch a
> > separate containing an inlined routine wasn't being built before
> > its callers.
> 
> Your Ada compiler is being unfriendly, but not inaccurate, i.e.
> the reference manual certainly permits the behavior you see. It
> is quite legitimate for a compiler to fail to inline something
> because the right body has not been compiled yet.

Yes, I'm happy that `pragma inline' is merely a request, and the
compiler we're using gives a warning when the routine can't be inlined
because it hasn't been compiled yet.  I should have been a little more
explicit;  one of the programs that comes with the compiler is meant to
examine a bunch of source and produce a linear order for compilation.
That program creates a dependency from the caller to the body of the
package containing the inlined routine, even when the routine is in a
separate.

> In systems where compilation order is important (unlike GNAT
> where this issue does not arise), the user is responsible for
> manually choosing the order of compilation that optimizes the
> use of inlining.

Agreed, except that the compiler comes with this program to ease our
manual burden.  It looks like we're stuck maintaining a manual order
for now.

> Consider the following:
> 
> [snip cyclic dependency example]
> 
> Since both of those cannot be true, only one of these calls can be
> inlined. The additional dependency will be created for the one that
> is inlined, assuring consistency, but one of the inlines will not
> happen.

Yep, I'm happy with that too;  if our source has a cycle then we'd be
quite happy to either break it by removing a pragma inline or moving
source around, or specify to the program which inline is more
important.

The current problem we're having doesn't involve any cycles.

> The only way to avoid this if you have a conventional Ada 83 style
> library is to do inlining at the binder stage, but this is quite
> expensive (I think the old Telesoft compiler did this).  Certainly
> the old Alsys compiler had the behavior described above.

Is there a diagram anywhere showing the various Ada compilers and their
lineage, if any?

> This often causes surprises, and means that order of compilation is
> crucial in such systems and must be worked out very carefully.
> Obviously no tool can do a fully automatic job, since in the above
> example, both requirements cannot be met, and it requires
> intervention to specify which of the two inlinings is more important.

In our case, it does seem that a tool could do a more correct
automatic job than it is currently doing.

> In GNAT, it is an absolute guarantee that the order in which
> compilations are done has no effect whatever on the generated code.

Yes, I agree it seems great (having never used it).  Must have been
strange at the time to go against the accepted wisdom and always refer
back to all the sources.

Thanks for the detailed response.


Ralph.

Re: Pragma Inline and its Effects of Compilation Dependencies.

[Ralph Corderoy]

Hi Samuel,

> This is a good area for ASIS based tools. I use just such a beast to
> help resolve this issue.

Can you expand on that?

> On the other hand, I have also found that compilation orders which
> general place bodies as soon as possible rarely have this problem so
> building a tool to handle this case may not be worth while if your
> tool can do bodies ASAP.

It does, but the routines to be inlined are normally in separates, not
the body, and due to the missing dependency they can be placed too
late in the order.

> > It seems what I need is something that will take many source files,
> > parse them, and spit out the dependencies for use in something like
> > a traditional makefile.  It isn't a trivial task as things like
> > package renames and use clauses help to obscure what is being
> > called.  Plus it mustn't make the mistake of thinking an inline
> > creates a dependency to the package body when a separate exists.
> > Does something like this exist?
> 
> This is easily written using ASIS queries. Lacking access to ASIS,
> one can get a yacc/lex grammars for Ada and do the extra work
> yourself. Hopefully, your compiler tool can spit out "normal"
> dependencies so you don't have to worry about context clauses.  You
> only have to worry about which subprograms are inlines and where they
> are called. Using syntax processes will easily handle straight
> subprogram calls but requires more work if your code is using rename
> declarations.

We might have access to ASIS but isn't that an interface to the DIANA
standard intermediate format?  Are you suggesting building everything
once, ignoring warnings about missed inline opportunities, and then use
ASIS to poke around the library to find the dependencies?

I've picked up a yacc grammar with lex parser from John Levine's
archive (one minor bug in the lexer), and it spits out some parts
easily enough.  Not sure if it is worth the hassle to add the necessary
rename handling, etc., code;  it might be easier for the project to
burn some man hours on maintaining the order manually over the next few
years.

> > This can't be an original problem.  What do people with large Ada
> > projects do?
> 
> Such things are important to your compiler selection.  If you need to
> change compilers in the future, support for this problem area needs
> to be on your list. In any event, you use what the compiler will give
> you and build anything else you need to the degree that it is worth
> building.

This is a project that is getting on for a decade old;  all the
hardware, OS, and compilers were specified years ago and we aren't
allowed to change them now.  Yes, development is still ongoing ;-)  We
could probably get away with an extra tool that worked out compilation
order for us though.


Ralph.

Re: Pragma Inline and its Effects of Compilation Dependencies.

[Ralph Corderoy]

Hi Robert,

> > The manual seemed to suggest it didn't consider source outside the
> > current library.
>
> That's confused, GNAT has no notion of library in that sense.  The
> only requirement is that all sources be available to the compilation
> process.

OK, thanks.  And having several thousand source files spread over
dozens of directories doesn't make this break down I guess.


Ralph.

Re: Pragma Inline and its Effects of Compilation Dependencies.

[Robert Dewar]

In article <8bd7oh$6sv$1@inputplus.demon.co.uk>,
  ralph@inputplus.demon.co.uk (Ralph Corderoy) wrote:
> Yes, I agree it seems great (having never used it).  Must have
> been strange at the time to go against the accepted wisdom and
> always refer back to all the sources.

Strange indeed :-)

The genesis of this idea was that Richard Stallman could not
believe that a language where the meaning of the program
depended on the order in which sources were compiled could
even vaguely be acceptable :-). We patiently explained that
the Ada RM required this, but he would not accept it, and
eventually we wouldn't accept it either, and the Ada 95
RM was reworded to make clear that this (acceptable)
interpretation of the Ada 83 RM is definitely legitimate :-)
When we explored this idea further, we found it had tremendous
advantages.

Robert Dewar


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Re: Pragma Inline and its Effects of Compilation Dependencies.

[Robert Dewar]

In article <8bd8d3$76s$1@inputplus.demon.co.uk>,
  ralph@inputplus.demon.co.uk (Ralph Corderoy) wrote:
> Hi Robert,
>
> > > The manual seemed to suggest it didn't consider source
outside the
> > > current library.
> >
> > That's confused, GNAT has no notion of library in that
sense.  The
> > only requirement is that all sources be available to the
compilation
> > process.
>
> OK, thanks.  And having several thousand source files spread
over
> dozens of directories doesn't make this break down I guess.


There are many ways of handling such a structure. One useful
option is gnatmake -i, which compiles everything in place,
putting new objects wherever the old ones were found, so that
once you have everything where you want it, gnatmake
automatically maintains this structure.


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Re: Pragma Inline and its Effects of Compilation Dependencies.

[Robert A Duff]

Robert Dewar <robert_dewar@my-deja.com> writes:

> The genesis of this idea was that Richard Stallman could not
> believe that a language where the meaning of the program
> depended on the order in which sources were compiled could
> even vaguely be acceptable :-).

And yet he seems perfectly happy with a language where the meaning of
the program depends on the order in which the object code is loaded into
the system -- Lisp.

I certainly agree that the source-based model is a good one, and I've
thought so since around 1984 or so.

There are really two aspects to the source-based model, as supported by
GNAT and the various compilers derived from the Intermetrics/AverStar
front end:

    1. The source is what matters.  If you change the source code,
       rebuilding tools notice.  Order of compilation doesn't matter.
       Compiling something twice produces the same result.  Etc.

    2. Symbol tables and whatnot are NOT stored in some sort of persistent
       data structure (disk files, or whatever), but are recomputed as
       needed.

These are somewhat independent design decisions.  That is, you could
have number 1, but as an optimization store symbol tables on disk, so
long as you make it a pure optimization (doesn't affect the semantics of
the source-based model).

Number 1 seems obviously Good to me.  I'm not so sure about number 2.
Clearly, not storing persistent data simplifies the compiler, which is a
good thing.  Especially since it won't *be* an optimization unless you go
to some trouble to make sure the data structures are reasonably small --
you can do a lot of compiling in the time it takes to read stuff from
the disk.

- Bob

Re: Pragma Inline and its Effects of Compilation Dependencies.

[Samuel T. Harris]

Ralph Corderoy wrote:
> 
> Hi Samuel,
> 
> > This is a good area for ASIS based tools. I use just such a beast to
> > help resolve this issue.
> 
> Can you expand on that?
> 
> > On the other hand, I have also found that compilation orders which
> > general place bodies as soon as possible rarely have this problem so
> > building a tool to handle this case may not be worth while if your
> > tool can do bodies ASAP.
> 
> It does, but the routines to be inlined are normally in separates, not
> the body, and due to the missing dependency they can be placed too
> late in the order.

I don't see why their being i separates presents a problem for
ASAP body order. The package body will be  placed in order as soon
as its extra supporters are in order. Assuming your separate has
no extra with clauses, then it will be placed immediately after
the parent body. Doing bodies ASAP means units dependent upon
the spec come after the body of the spec!

> 
> > > It seems what I need is something that will take many source files,
> > > parse them, and spit out the dependencies for use in something like
> > > a traditional makefile.  It isn't a trivial task as things like
> > > package renames and use clauses help to obscure what is being
> > > called.  Plus it mustn't make the mistake of thinking an inline
> > > creates a dependency to the package body when a separate exists.
> > > Does something like this exist?
> >
> > This is easily written using ASIS queries. Lacking access to ASIS,
> > one can get a yacc/lex grammars for Ada and do the extra work
> > yourself. Hopefully, your compiler tool can spit out "normal"
> > dependencies so you don't have to worry about context clauses.  You
> > only have to worry about which subprograms are inlines and where they
> > are called. Using syntax processes will easily handle straight
> > subprogram calls but requires more work if your code is using rename
> > declarations.
> 
> We might have access to ASIS but isn't that an interface to the DIANA
> standard intermediate format?  Are you suggesting building everything
> once, ignoring warnings about missed inline opportunities, and then use
> ASIS to poke around the library to find the dependencies?

Not all compiler use DIANA trees. ASIS is a standard way to query
the semantic nature of the program, regardless of its internal
representation. ASIS code should be very portable across
supported compilers.

What I am suggesting is using a tool to capture ALL the dependencies
(i.e. with clauses, generic bodies to their instantiations, pragma
inline bodies, anything else you need) before initial compilation.

However, as you point out, using the warning for failed inlines
as feedback is also a alternative course of action. Given a
"normal" dependency list, one can simply add more entries
based on the inline warning you get. The problem with this is
that you never know when you'll be done. Changes to code can
siginficantly change the base order and cause more inline
warnings. Your initial order may satisfy some inlining so these
won't be captured explicitly in your dependency list.

> 
> I've picked up a yacc grammar with lex parser from John Levine's
> archive (one minor bug in the lexer), and it spits out some parts
> easily enough.  Not sure if it is worth the hassle to add the necessary
> rename handling, etc., code;  it might be easier for the project to
> burn some man hours on maintaining the order manually over the next few
> years.

I gave up on this approach for any but the most basic stuff
years ago when I discovered ASIS. It is much more work to do
anything useful especially on a large project. ASIS is so much
easier, but does have its own learning curve.

> 
> > > This can't be an original problem.  What do people with large Ada
> > > projects do?
> >
> > Such things are important to your compiler selection.  If you need to
> > change compilers in the future, support for this problem area needs
> > to be on your list. In any event, you use what the compiler will give
> > you and build anything else you need to the degree that it is worth
> > building.
> 
> This is a project that is getting on for a decade old;  all the
> hardware, OS, and compilers were specified years ago and we aren't
> allowed to change them now.  Yes, development is still ongoing ;-)  We
> could probably get away with an extra tool that worked out compilation
> order for us though.

There is a distinct difference between development compiler and
target compiler. Many project use the same compiler for both, but
we all must recognize that this does not need to be the case.
Say I use compiler X for development and target execution. Compiler
X does not provide an ASIS interface. I find that I need to write
some ASIS tools to do various things. I find compiler Y which
supports ASIS. I use compiler Y on the same source simply to
run the ASIS queries. If your doing Ada 95, GNAT is free and
fully supports ASIS.

> 
> Ralph.

-- 
Samuel T. Harris, Principal Engineer
Raytheon, Aerospace Engineering Services
"If you can make it, We can fake it!"

Re: Pragma Inline and its Effects of Compilation Dependencies.

[Robert Dewar]

In article <38DBBD73.61A5F5E4@Raytheon.com>,
  "Samuel T. Harris" <samuel_t_harris@Raytheon.com> wrote:

> Not all compiler use DIANA trees

In fact I think the *only* compiler that uses DIANA trees
now is Rational, isn't that the case? I think the old
Systeam compiler used DIANA too, but basically DIANA failed
completely in its original mission as an implementation
independent representation format.

ASIS was the technology that developed out of DIANA, basically
it provides a more appropriate abstract layer which can be
applied to a wide variety of intermediate strucures, and is
thus more appropriate for achieving compiler indepedence.

DIANA prescribes a number of important choices in a compiler,
and many Ada compiler designers have felt that it was simply
not a desirable choice.

That of course is the kind of thing which competition in the
market place should determine (rather than an external
standard), which is why ASIS has succeeded where DIANA failed
(as a common intermediate language, I am not saying that it is
not possible to use DIANA in an Ada 95 compiler, since obviously
the Rational technology is a counter example).



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