Re: optimization/8746: gcc-3 miscompiles Linux kernel ppa driver on x86

Re: optimization/8746: gcc-3 miscompiles Linux kernel ppa driver on x86

[ebotcazou]

Synopsis: gcc-3 miscompiles Linux kernel ppa driver on x86

State-Changed-From-To: open->feedback
State-Changed-By: ebotcazou
State-Changed-When: Tue Feb 18 13:51:53 2003
State-Changed-Why:
    Could you provide us with a minimal and compilable testcase?
    See http://gcc.gnu.org/bugs.html

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8746

Re: optimization/8746: gcc-3 miscompiles Linux kernel ppa driver on x86

[Carsten Haustein]

The following reply was made to PR optimization/8746; it has been noted by GNATS.

From: Carsten Haustein <chaus@rz.uni-potsdam.de>
To: <ebotcazou@gcc.gnu.org>, <chaus@rz.uni-potsdam.de>, <gcc-bugs@gcc.gnu.org>,
   <gcc-prs@gcc.gnu.org>, <nobody@gcc.gnu.org>, <gcc-gnats@gcc.gnu.org>
Cc:  
Subject: Re: optimization/8746: gcc-3 miscompiles Linux kernel ppa driver on
 x86
Date: Fri, 28 Feb 2003 17:26:26 +0100 (MET)

   This message is in MIME format.  The first part should be readable text,
   while the remaining parts are likely unreadable without MIME-aware tools.
   Send mail to mime@docserver.cac.washington.edu for more info.
 
 ---559023410-1804928587-1046449586=:26411
 Content-Type: TEXT/PLAIN; charset=US-ASCII
 
 Compile the testcase with: gcc -O -march=i{345}86 -o check check.c
 Run the test with: check <number>, where <number> is an integer between 0
 and 255 (without angle brackets). The program will "prove" that any number
 in this range is less than 128, which is obviously wrong.
 
 Some notes:
 1. It is important to select one of the shown -march arguments. Only code
 generated for i{345}86 and K6 family is affected. Code generated for i686
 family, Pentium 4 and Athlon family works fine. This code uses the al
 register for applying the bit-mask instead of eax and a different
 representation of the immediate 0xf0.
 
 2. There must not be a statement between the "and" operation and the
 if-expression. Otherwise code is generated for both the "and" operation
 and for testing the MSB, since the extra statement may affect the
 cpu-flags. Such code works fine.
 
 3. The value assigned to r must be examined in one or the other way.
 Otherwise code for the "and" operation will be omitted and code for
 testing the MSB will be generated, which leads to working code too.
 
 --
 
 Carsten Haustein
 
 ---559023410-1804928587-1046449586=:26411
 Content-Type: TEXT/PLAIN; charset=US-ASCII; name="check.c"
 Content-Transfer-Encoding: BASE64
 Content-ID: <Pine.GSO.4.30.0302281726260.26411@persius.rz.uni-potsdam.de>
 Content-Description: 
 Content-Disposition: attachment; filename="check.c"
 
 I2luY2x1ZGUgPHN0ZGlvLmg+DQppbnQgbWFpbihpbnQgYXJnYywgY2hhciAq
 YXJndltdKSB7DQogICB1bnNpZ25lZCBjaGFyIHIgPSAoYXRvaShhcmd2WzFd
 KSkgJiAweGYwOw0KICAgaWYgKCEociAmIDB4ODApKSBwcmludGYoIiV1IDwg
 MTI4XG4iLCByKTsNCiAgICAgICAgICAgICAgIGVsc2UgcHJpbnRmKCIldSA+
 PSAxMjhcbiIsIHIpOw0KICAgcmV0dXJuIDA7DQp9DQo=
 ---559023410-1804928587-1046449586=:26411--