Re: [PATCH] c/67925 - update documentation on `inline'

[Arkadiusz Drabczyk <arkadiusz at drabczyk dot org>]

On Wed, Oct 14, 2015 at 08:36:43AM -0600, Martin Sebor wrote:
> On 10/13/2015 04:47 PM, Arkadiusz Drabczyk wrote:
> >* gcc/doc/extend.texi: documentation says that functions declared
> >`inline' would not be integrated if they are called before they are
> >defined or if they are recursive. Both of these statements is now
> >false as shown in examples on Bugzilla.
> 
> It might also be worth updating the note in the subsequent
> paragraph and removing the mention of variable-length data types
> which no longer prevent inlining.

Done.  I also removed the mention of nested functions as the following
code compiled with GCC 6.0 doesn't give any warning with -O2 -Winline
and main() is the only function defined in assembler code:

#include <stdio.h>
#include <stdlib.h>

inline static int foo (int a, int b)
{
	printf("a == %d\n", a);
	inline int square (int z) { return z * z; }

	return square (a) + square (b);
}

int main(int argc, char *argv[])
{
	printf("%d\n", foo(atoi(argv[1]), atoi(argv[2])));
	exit(0);
}

I also removed a reference to Bugzilla from the commit message, I
don't think it's necessary.

> FWIW, the list of most -Winline warnings issued by GCC is here
> (there are two more in Ada which, AFAICT, have to do with nested
> functions):
> 
> $ grep -A1 "can never be inlined" gcc/tree-inline.c
> (...)
> --
> 	      = G_("function %q+F can never be inlined because "
> 		   "it uses non-local goto");

I tested of all of these and listed them in the documentation but
wasn't able to reproduce this one.  The following code does not give
any warning with -O2 -Winline:

#include <stdio.h>
#include <stdlib.h>
#include <setjmp.h>

static jmp_buf buf;

inline static void longjmp_test(int n)
{
	puts("hi");

	if (n == 2)
		longjmp(buf, 2);
}

int main(int argc, char *argv[])
{
	printf("%d\n", setjmp(buf));
	longjmp_test(atoi(argv[1]));
	puts("next line in a normal execution");
	exit(0);
}

Is this test case correct?  However, I get the following warning using
__builtin_longjmp() instead of longjmp():

warning: function 'longjmp_test' can never be inlined because it uses
setjmp-longjmp exception handling [-Winline]
>8------------------------------------------------------8<
* gcc/doc/extend.texi: documentation says that functions declared
`inline' would not be integrated if they are called before they are
defined, if they are recursive, if they use variable-length data types
or if they are nested.  All of these statements are now false and have
been removed. Mention of setjmp(), __builtin_return() and
__builtin_apply_args() has been added.
---
 gcc/doc/extend.texi | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 79440d3..be95cc3 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -7088,21 +7088,18 @@ function are integrated into the caller, and the function's address is
 never used, then the function's own assembler code is never referenced.
 In this case, GCC does not actually output assembler code for the
 function, unless you specify the option @option{-fkeep-inline-functions}.
-Some calls cannot be integrated for various reasons (in particular,
-calls that precede the function's definition cannot be integrated, and
-neither can recursive calls within the definition).  If there is a
-nonintegrated call, then the function is compiled to assembler code as
-usual.  The function must also be compiled as usual if the program
-refers to its address, because that can't be inlined.
+If there is a nonintegrated call, then the function is compiled to
+assembler code as usual.  The function must also be compiled as usual if
+the program refers to its address, because that can't be inlined.
 
 @opindex Winline
 Note that certain usages in a function definition can make it unsuitable
-for inline substitution.  Among these usages are: variadic functions, use of
-@code{alloca}, use of variable-length data types (@pxref{Variable Length}),
-use of computed goto (@pxref{Labels as Values}), use of nonlocal goto,
-and nested functions (@pxref{Nested Functions}).  Using @option{-Winline}
-warns when a function marked @code{inline} could not be substituted,
-and gives the reason for the failure.
+for inline substitution.  Among these usages are: variadic functions,
+use of @code{alloca}, use of computed goto (@pxref{Labels as Values}),
+use of @code{setjmp} and use of @code{__builtin_return} or
+@code{__builtin_apply_args}.  Using @option{-Winline} warns when a
+function marked @code{inline} could not be substituted, and gives the
+reason for the failure.
 
 @cindex automatic @code{inline} for C++ member fns
 @cindex @code{inline} automatic for C++ member fns
-- 
2.3.5


-- 
Arkadiusz Drabczyk <arkadiusz@drabczyk.org>