[Bug c/56125] New: -O2 -ffast-math generates bad code when dividing a double by the square of another double.

[mednafen at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56125



             Bug #: 56125

           Summary: -O2 -ffast-math generates bad code when dividing a

                    double by the square of another double.

    Classification: Unclassified

           Product: gcc

           Version: 4.7.2

            Status: UNCONFIRMED

          Severity: normal

          Priority: P3

         Component: c

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: medna...@gmail.com





Created attachment 29288

  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29288

Test program.



XXX@willow:~$ gcc -O0 -o weird weird.c 

XXX@willow:~$ ./weird 

7.250000



XXX@willow:~$ gcc -O2 -o weird weird.c 

XXX@willow:~$ ./weird 

7.250000



XXX@willow:~$ gcc -ffast-math -O2 -o weird weird.c 

XXX@willow:~$ ./weird 

5.126524







Using built-in specs.

COLLECT_GCC=gcc

COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.7/lto-wrapper

Target: x86_64-linux-gnu

Configured with: ../src/configure -v --with-pkgversion='Debian 4.7.2-5'

--with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs

--enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr

--program-suffix=-4.7 --enable-shared --enable-linker-build-id

--with-system-zlib --libexecdir=/usr/lib --without-included-gettext

--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7

--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu

--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object

--enable-plugin --enable-objc-gc --with-arch-32=i586 --with-tune=generic

--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu

--target=x86_64-linux-gnu

Thread model: posix

gcc version 4.7.2 (Debian 4.7.2-5)