Date:	Sat, 09 Jun 2001 09:48:42 +0300
From:	"Eli Zaretskii" <eliz AT is DOT elta DOT co DOT il>
Sender:	halo1 AT zahav DOT net DOT il
To:	Martin Str|mberg <ams AT ludd DOT luth DOT se>
Message-Id:	<7263-Sat09Jun2001094842+0300-eliz@is.elta.co.il>
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CC:	djgpp-workers AT delorie DOT com
In-reply-to:	<200106082135.XAA13989@mother.ludd.luth.se> (message from Martin
	Str|mberg on Fri, 8 Jun 2001 23:35:39 +0200 (MEST))
Subject:	Re: Compiler options for djdev build
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> From: Martin Str|mberg <ams AT ludd DOT luth DOT se>
> Date: Fri, 8 Jun 2001 23:35:39 +0200 (MEST)
> > 
> >   -Wundef
> >   -Wcast-align
> >   -Wconversion
> >   -Wsign-compare
> > 
> > I didn't yet try to build the library with these; perhaps someone
> > could try that.
> 
> I did.

Thanks!

> We get a lot of warnings. Here's some diffs reflecting changes
> necessary (hand-pasted in):
> 
> Index: src/libc/ansi/locale/mbstowcs.c
> ===================================================================
> RCS file: /cvs/djgpp/djgpp/src/libc/ansi/locale/mbstowcs.c,v
> retrieving revision 1.1
> diff -p -u -r1.1 mbstowcs.c
> --- src/libc/ansi/locale/mbstowcs.c     1994/11/29 09:18:20     1.1
> +++ src/libc/ansi/locale/mbstowcs.c     2001/06/08 21:19:36
> @@ -4,8 +4,8 @@
>  size_t
>  mbstowcs(wchar_t *wcs, const char *s, size_t n)
>  {
> -  int i;
> -  for (i=0; s[i] && (i<n-1); i++)
> +  size_t i;
> +  for (i=0; s[i] && (i+1<n); i++)
>      wcs[i] = s[i];

This sounds like a kind of change that indeed should have been made.
Mixing signed and unsigned is not a good idea.

> > Finally, do we still need -fno-strength-reduce?  I'd think we could
> > remove that now.  If we are not sure, perhaps someone could ask on the
> > GCC mailing list.
> 
> I'm trying with that one removed.

Thanks.  I think that -fno-strength-reduce was introduced because some
old versions of GCC would sometimes produce incorrect code if this
optimization were not removed.  We should probably ask the GCC
maintainers whether that problem is gone on x86 in GCC 2.9x series.

> Some warnings I don't understand and can't get to go away (I only
> tried to remove the todigit ones and gave up):
> 
> make -C ansi/stdio 
> gcc ... -c doprnt.c
> cc1.exe: warnings being treated as errors
> doprnt.c: In function `_doprnt':
> doprnt.c:167: warning: passing arg 1 of `todigit' with different width due to prototype

Change `todigit' (near the beginning of doprnt.c) to accept an int
instead of a char, and the warning will go away.

DJ, is there any particular reason that you defined todigit as
accepting a char?  If the issue is efficiency, we could examine the
machine code produced by GCC now; I'd guess it won't change, if GCC
gets its optimizations right.

> doprnt.c:277: warning: passing arg 5 of `cvtl' with different width due to prototype

Similar probl;em: `cvtl's prototype says its 5th argument is a char.

Basically, this warning alerts you to any function whose prototype
modifies the default promotion of arguments.  This flags functions
whose prototypes include char, short, and float arguments.  IMHO,
these practices are unsafe and should be avoided.

> Finally an observation. Look at doscan.c above. We have variables
> declared as register. As I understand this this make optimisation by
> the compiler difficult. Shouldn't we change to not use "register"?

There shouldn't be a reason to do that.  The `register' qualifier is
just a hint to the compiler as to what variables the programmer would
like to be in registers in the first priority.  The compiler is free
to do whatever it wants with that, including ignore them altogether.

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