Date: Wed, 07 Oct 1998 08:31:57 -0700 From: Mike Smith <mike@smith.net.au> To: marko@cs.uni-frankfurt.de Cc: freebsd-stable@FreeBSD.ORG Subject: Re: Global register variables in gcc and stdio.h?!? Message-ID: <199810071531.IAA00355@dingo.cdrom.com> In-Reply-To: Your message of "Wed, 07 Oct 1998 15:30:38 %2B0200." <199810071330.PAA22126@king.ki.informatik.uni-frankfurt.de>
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> An application I want to compile runs much faster if it can use global
> register variables.
>
> Trying to compile it I get
>
> [...]
> gmake[1]: Entering directory `/usr/home/marko/src/mercury-0.7.3.orig/runtime'
> MERCURY_C_INCL_DIR=. ../scripts/mgnuc --grade asm_fast.gc --no-ansi -I../runtime -I../boehm_gc -g -c label.c -o label.o
> In file included from regs.h:67,
> from imp.h:36,
> from label.c:19:
> machdeps/i386_regs.h:61: global register variable follows a function definition
> machdeps/i386_regs.h:62: global register variable follows a function definition
> machdeps/i386_regs.h:67: global register variable follows a function definition
> gmake[1]: *** [label.o] Error 1
> gmake[1]: Leaving directory `/usr/home/marko/src/mercury-0.7.3.orig/runtime'
> gmake: *** [runtime] Error 2
>
> I checked the preprocessor output and found that there is only the
> function definition for `static __inline int __sputc(int _c, FILE
> *_p)` which is included from stdio.h. Depending on an #ifdef that
> version of __sputc or an alternative as a macro is used.
>
> I would suggest adding something like
> !defined(__USE_GLOBAL_REGISTER_VARIABLES__) to the condition for using
> the inline function.
>
> Doing that allows at least mercury to compile using global register
> variables.
>
> Please comment.
1) Any application which depends on global register variables for
performance needs to be fixed. The concept of a "global register
variable" on the x86 is a bit of a joke anyway.
2) Declare your global register variables before including header
files.
--
\\ Sometimes you're ahead, \\ Mike Smith
\\ sometimes you're behind. \\ mike@smith.net.au
\\ The race is long, and in the \\ msmith@freebsd.org
\\ end it's only with yourself. \\ msmith@cdrom.com
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