Date: Mon, 17 Feb 2014 17:45:12 GMT From: David Hines <freebsd@dph.fluff.org> To: freebsd-gnats-submit@FreeBSD.org Subject: i386/186848: CLANG/LLVM code generation bug with optimisation on i386 Message-ID: <201402171745.s1HHjCsG010826@cgiserv.freebsd.org> Resent-Message-ID: <201402171750.s1HHo0Ek061734@freefall.freebsd.org>
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>Number: 186848
>Category: i386
>Synopsis: CLANG/LLVM code generation bug with optimisation on i386
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-i386
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Mon Feb 17 17:50:00 UTC 2014
>Closed-Date:
>Last-Modified:
>Originator: David Hines
>Release: FreeBSD 10.0-RELEASE #0 r260789
>Organization:
>Environment:
FreeBSD free100 10.0-RELEASE FreeBSD 10.0-RELEASE #0 r260789: Fri Jan 17 01:46:25 UTC 2014 root@snap.freebsd.org:/usr/obj/usr/src/sys/GENERIC i386
>Description:
"cc -O -o clang_bug-O clang_bug.c" generates incorrect code on i386, with the attached sample code. Without the "-O", or on an amd64 install the problem does not occur.
>How-To-Repeat:
Compile and run the attached programme.
When this is compiled without optimisation the output is correct.
cc -o clang_bug clang_bug.c; ./clang_bug
An int has 32 bits
With optimisation it is incorrect.
cc -O -o clang_bug-O clang_bug.c; ./clang_bug-O
An int has 33 bits
>Fix:
No fix known. Work-arounds include not using optimiser, or using gcc.
Patch attached with submission follows:
# This is a shell archive. Save it in a file, remove anything before
# this line, and then unpack it by entering "sh file". Note, it may
# create directories; files and directories will be owned by you and
# have default permissions.
#
# This archive contains:
#
# clang_bug.c
#
echo x - clang_bug.c
sed 's/^X//' >clang_bug.c << '7cdc9fc910e8be01c1758f1d1bf4e799'
X#include <stdio.h>
X
X/*
X * This demonstrates a bug in the code generation of the C compiler
X * distributed as part of FreeBSD 10.0 on i386 when using optimisation.
X *
X * To identify the affected system:
X * Output from uname -ap:
X * FreeBSD free100 10.0-RELEASE FreeBSD 10.0-RELEASE #0 r260789:
X * Fri Jan 17 01:46:25 UTC 2014
X * root@snap.freebsd.org:/usr/obj/usr/src/sys/GENERIC i386 i386
X * Output from cc -v:
X * FreeBSD clang version 3.3 (tags/RELEASE_33/final 183502) 20130610
X * Target: i386-unknown-freebsd10.0
X * Thread model: posix
X *
X * When this is compiled without optimisation the output is correct.
X * cc -o clang_bug clang_bug.c; ./clang_bug
X * An int has 32 bits
X *
X * With optimisation it is incorrect.
X * cc -O -o clang_bug-O clang_bug.c; ./clang_bug-O
X * An int has 33 bits
X */
X
Xunion
X{
X int i;
X} u;
X
X
Xint
Xmain(int argc, char *argv[])
X{
X int j = 1;
X
X for (u.i = 1; u.i += u.i; ++j)
X ;
X printf("An int has %d bits\n", j);
X
X return 0;
X}
7cdc9fc910e8be01c1758f1d1bf4e799
exit
>Release-Note:
>Audit-Trail:
>Unformatted:
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