From: Michael Widenius <monty AT monty DOT pp DOT sci DOT fi>
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Message-ID: <14455.31978.6456.97304@monty.pp.sci.fi>
Date: Sat, 8 Jan 2000 20:07:38 +0200 (EET)
To: pgcc AT delorie DOT com
Subject: pgcc on AMD K6
X-Mailer: VM 6.72 under 21.1 (patch 7) "Biscayne" XEmacs Lucid
Reply-To: pgcc AT delorie DOT com


Hi!

I tried to run a file compiled with the following options on my AMD
K6-3 400 Mhz Linux RedHat 6.1 machine:

((/my/monty/master/mysql-3.23.8-alpha/mysys)) /usr/local/pgcc/bin/gcc -v
Reading specs from /usr/local/pgcc/lib/gcc-lib/i686-pc-linux-gnu/pgcc-2.95.2/specs
gcc version pgcc-2.95.2 19991024 (release)


((/my/monty/master/mysql-3.23.8-alpha/mysys)) /usr/local/pgcc/bin/gcc -I./../include -I../include -I.. -DDBUG_OFF -O6 -mpentiumpro -fomit-frame-pointer -S mf_dirname.c


-------
#include "mysys_priv.h"
#include <m_string.h>

uint dirname_part(my_string to, const char *name)
{
  uint length;
  DBUG_ENTER("dirname_part");
  DBUG_PRINT("enter",("'%s'",name));

  length=dirname_length(name);
  (void) strmake(to,(char*) name,min(length,FN_REFLEN-2));
  convert_dirname(to);				/* Convert chars */
  DBUG_RETURN(length);
} /* dirname */
-------------

This produced the following output:

dirname_part:
        subl $16,%esp
        pushl %edi
        pushl %esi
        pushl %ebx
        movl 32(%esp),%edi
        movl 36(%esp),%esi
        pushl %eax
        pushl %eax
        pushl $58
        pushl %esi
        call strrchr
        movl %eax,%edx
        leal -1(%esi),%eax
        testl %edx,%edx
        cmove %eax,%edx                # <- This doesn't work
        addl $16,%esp
        movl %edx,%ecx
        leal 1(%ecx),%edx
 
....

My K6-III computer crashes with an illegal instruction at the cmove
instruction, while my Pentium II computer (running Suse 6.2) works perfectly.

I also noticed that I can't start pgcc on the K6-III computer;  It
also dies with an 'illegal instruction'.

Is the cmove instruction not supported by AMD K6 and in this case why
is pgcc generating it when one only uses the safe -mcpu instead of the
-march=cpu option?

Previous versions of pgcc have worked ok on the K6 machine, so
something has changed recently.

Regards,
Monty
Moderator of MySQL

PS: By the way, I am very impressed with the code pgcc generates for a
    lot of functions involving longlong:s on Intel;  It's a LOT better
    Codefusion, gcc 2.95.2 or the Fujitsu C++ compiler!  Good work!