From: "Alexei A. Frounze" <alex DOT fru AT mtu-net DOT ru>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: THE -O2 PROBLEM
Date: Sat, 15 Apr 2000 20:19:17 +0400
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To: djgpp AT delorie DOT com
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Dieter Buerssner wrote:
> 
> Alexei A. Frounze wrote:
> 
> >I'm going to change that stupid "g" constraint. I'll replace it with
> >others ("r" and "m" or even with particular registers, if needed).
> 
> I hope you are aware, that you cannot just change "g" to "m", that
> wouldn't work. You have to get rid of all those stupid references
> as well.

I didn't put any "m"s, just replaced "g" with "r" or a particular register name.


Btw, does GCC support both natations of register names as parameters to inline
assembly like this:

  : "a"(), "b"(), "c"(), "d"(), "S"(), "D"()

and

  : "eax"(), "ebx"(), "ecx"(), "edx"(), "esi"(), "edi"()


Seems it compiles both. Right?

> \begin{rant}
> I still think, it is stupid, that gcc made this non back compatible
> change with the clobbered input registers. 

...

> \end{rant}

Sure. I have a 3d engine written for older version of GCC. And it doesn't
compile now because of the clobbered register list. 

I.e. if a parameter is passed to the inline assembly block defineteyl via EAX
register:

: "a" (variable), ...

and the same register (EAX) is in the clobbered list, GCC stops with a error
message. Don't remember what exactly it says, but it's a very bad behaviour.
Newer versions should definetely have support for old syntax.

> Probably I shouldn't tell you Alexei, but if you wouldn't have
> used all those unnecessary references, "g" would even have worked
> with floating point variables.

But what I'd do then? I'd need inline asm anyway, so I might give up with GCC or
finally switch to external assembly functions instead of any inlining.


thanks.
Alexei A. Frounze
-----------------------------------------
Homepage: http://alexfru.chat.ru
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