$ gcc -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with:
/var/tmp/portage/sys-devel/gcc-4.4.0_pre9999/work/gcc-4.4.0-9999/configure
--prefix=/usr --bindir=/usr/i686-pc-linux-gnu/gcc-bin/4.4.0-pre9999
--includedir=/usr/lib/gcc/i686-pc-linux-gnu/4.4.0-pre9999/include
--datadir=/usr/share/gcc-data/i686-pc-linux-gnu/4.4.0-pre9999
--mandir=/usr/share/gcc-data/i686-pc-linux-gnu/4.4.0-pre9999/man
--infodir=/usr/share/gcc-data/i686-pc-linux-gnu/4.4.0-pre9999/info
--with-gxx-include-dir=/usr/lib/gcc/i686-pc-linux-gnu/4.4.0-pre9999/include/g++-v4
--host=i686-pc-linux-gnu --build=i686-pc-linux-gnu --disable-altivec
--disable-fixed-point --enable-nls --without-included-gettext
--with-system-zlib --disable-checking --disable-werror --enable-secureplt
--disable-multilib --enable-libmudflap --disable-libssp --disable-libgomp
--enable-cld --disable-libgcj --with-arch=i686 --enable-languages=c,c++
--enable-shared --enable-threads=posix --enable-__cxa_atexit
--enable-clocale=gnu --with-bugurl=http://bugs.gentoo.org/ --with-pkgversion=
Thread model: posix
gcc version 4.4.0-pre9999 built 20090310 (Gentoo SVN ebuild) rev. 144732 ()
The command to trigger the bug:
gcc prdtoa.i -g -c -O2
The symptom of the bug:
In the output of objdump -S -l prdtoa.o
/tmp/prdtoa.c:1837
#endif
/* rv = */ rounded_product(dval(rv), tens[e]);
goto ret;
#endif
}
i = DBL_DIG - nd;
These 6 lines of code only generate one instruction
25de: ba 25 00 00 00 mov $0x25,%edx
If use gcc 4.3.3, the output is like this:
/tmp/prdtoa.c:1833
if (sign) {
rv = -rv;
sign = 0;
}
#endif
/* rv = */ rounded_product(dval(rv), tens[e]);
284e: 8b 5d 90 mov -0x70(%ebp),%ebx
2851: dd 45 d0 fldl -0x30(%ebp)
2854: dc 0c dd e0 00 00 00 fmull 0xe0(,%ebx,8)
285b: 8b 5d 98 mov -0x68(%ebp),%ebx
285e: e9 cd fd ff ff jmp 2630 <PR_strtod+0x210>
2863: 90 nop
2864: 8d 74 26 00 lea 0x0(%esi,%eiz,1),%esi
The impact of this bug:
prdtoa.c is from NSPR, NetScape Portable Runtime, which is used by firefox.
This bug will cause font size of certain tags become extremely large because of
the abnormal behavior of function PR_strtod. For example, given "1.5" as a
parameter, PR_strtod will return 15.0. I found this when trying firefox on N32
ABI Loongson system. Since Loongson specific support only avaiable in gcc 4.4.
Will post the prdtoa.i soon.
--
Summary: [4.4 Regression] code mistakenly optimized out when -O2
is enabled
Product: gcc
Version: 4.4.0
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: regression
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: r0bertz at gentoo dot org
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39418
