Sender: nate AT cartsys DOT com
Message-ID: <35A2F822.A7348571@cartsys.com>
Date: Tue, 07 Jul 1998 21:40:02 -0700
From: Nate Eldredge <nate AT cartsys DOT com>
MIME-Version: 1.0
To: soltesz AT hotmail DOT com
CC: djgpp AT delorie DOT com
Subject: Re: gcc optimizing bug
References: <35A27937 DOT E89D5F1B AT hotmail DOT com>
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Archee/CoNTRACT wrote:
> 
> hi !
> 
> I use many ASM in my demos.
> When I switch on -O9 it produces a crashing exe.
> I gave only -O2, than it worked.
> What can by wrong ?

Is this regular GCC, or PGCC?  PGCC is apparently unstable at very high
-O levels. For regular GCC, nothing above -O3 has any additional effect.
 
> How can I reach the best optimizing without any danger ?
>
> How can I use gcc with optimizing without bugz ?

Nobody knows what bugs may exist in GCC, so your questions cannot be
answered.

> What registers can I modify in an ASM code ?

In inline asm, you must inform the compiler of all registers you
clobber.  In an external asm function, you can modify eax, ecx, edx, and
the FPU registers; all others must be saved and restored.  Perhaps that
is the cause of your crash?

In the case of inline asm, there were a few subtle bugs in GCC 2.7.2.1;
you might upgrade to 2.8.1, if you haven't, and see if that helps. 
Otherwise, compile with -S and check that the code is actually correct. 
I haven't checked whether they're fixed, because I lost the test cases.
-- 

Nate Eldredge
nate AT cartsys DOT com