Sender: nate AT cartsys DOT com
Message-ID: <35F2BA6C.F2015C97@cartsys.com>
Date: Sun, 06 Sep 1998 09:38:04 -0700
From: Nate Eldredge <nate AT cartsys DOT com>
MIME-Version: 1.0
To: Ilya Ryzhenkov <orangy AT inetlab DOT com>
CC: djgpp workers list <djgpp-workers AT delorie DOT com>
Subject: Re: Preventing compiler from expanding inline
References: <35F1B0BD DOT 707A60C7 AT inetlab DOT com>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Precedence: bulk

Ilya Ryzhenkov wrote:
> 
> Hi again, I hope I don't annoy anyone ;-)
> 
> Just a simple question - is there any method to prevent
> specific function from expanding inline ? I don't mean
> global -f option, I think of something like function
> attribute or #pragma or whatever else.

If you don't declare it `inline' and optimize with less than `-O3',
AFAIK, it won't be inlined.

But if you need it declared `inline' for other occurences, I don't know
how you can force a call in some place.  Except of course

inline void foo() { /* ... */ }

...
((void (volatile *)())&foo)();

> Does anybody knows how gcc decides (under normal conditions, i.e
> no overrides like inline keyword or inline restrictions)
> when to expand function (class member) inline ? Is it size
> condition, or complexity or something else ?

Okay.  To even consider inlining a function, one of the following must
be true:

* The function is declared `inline'.
* The file is being compiled with `-O3' or `-finline-functions'.

That is true in C, at least.  In C++, I assume defining the function
inside the class will do it too.

And:

* It must already have been defined at the point where it's used.

Then, the test for whether a function may be inlined is in
`integrate.c', in function `function_cannot_inline_p'.  Basically, if
any of the following are true, the function will not be inlined.

* Uses varargs.
* Uses alloca.
* Has nested functions.
* Returns a structure in registers.
* Has an argument of a varying-size structure, or returns one. (I don't
know what that means.)
* Has more than INTEGRATE_THRESHOLD insns.  This seems to be something
like 8 * (number of args + 8).
* Has a nonlocal goto.
* Several other complicated cases.  Read the source.

If you compile with `-Winline', the compiler will warn when a function
that should be inlined cannot be (i.e. passes the first test but fails
the second), and it will explain why.

> I need it to prevent constructors of some classes from
> expanding inline. I need a real call instruction to them
> everywhere they are used.

You could define it outside the class, perhaps?
-- 

Nate Eldredge
nate AT cartsys DOT com