[Bug c++/36860] New: gcc 4.2.3 produces poor code compared to gcc-3.4.3 on xeon prestonia

["jeff at jeffunit dot com" <gcc-bugzilla at gcc dot gnu dot org>]

I have a subroutine that is heavily used by a program I frequently run called
UKKA_Dist_With_Max. I had benchmarked it using mandriva linux 2005LE. When I
ran it using mandriva 2008.1, it ran much slower. Using the compiler from
mandriva linux 2005LE (gcc-3.4.3) and mandriva 2008.1, I was able to reproduce
the problem.
For example, with gcc-3.4.3 a small run takes 191 seconds, but with gcc-4.2.3
the
same run takes 247 seconds.

The switches I am using to compile, with both compilers are:
-O3 -march=pentium4 -mtune=pentium4 -g -pthread \
                -finline-functions -fschedule-insns2 -fbounds-check \
                -W -Wall -pedantic -Wshadow -Wpointer-arith -Weffc++ \
                -Wcast-qual -Wcast-align -Wwrite-strings -Wunused \
                -Wctor-dtor-privacy -Wnon-virtual-dtor -Wreorder \
                -Woverloaded-virtual -Wsign-promo -Wunused-parameter \
                -Wpointer-arith -Wreturn-type -Wcast-qual -Wswitch \
                -Wshadow -Wcast-align \
                -Wchar-subscripts -Winline -Wredundant-decls

gcc-4.2.3 was prebuilt by mandriva with the following:
Using built-in specs.
Target: i586-manbo-linux-gnu
Configured with: ../configure --prefix=/usr --libexecdir=/usr/lib
--with-slibdir=/lib --mandir=/usr/share/man --infodir=/usr/share/info
--enable-checking=release
--enable-languages=c,c++,ada,fortran,objc,obj-c++,java
--host=i586-manbo-linux-gnu --with-cpu=generic --with-system-zlib
--enable-threads=posix --enable-shared --enable-long-long --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-clocale=gnu --enable-java-awt=gtk
--with-java-home=/usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre --enable-gtk-cairo
--disable-libjava-multilib --enable-ssp --disable-libssp
Thread model: posix
gcc version 4.2.3 (4.2.3-6mnb1)

gcc-3.4.3 was built by me with the following:
Reading specs from /home/jdeifik_2008.1/lib/gcc/i686-pc-linux-gnu/3.4.3/specs
Configured with: ../gcc-3.4.3/configure --prefix=/home/jdeifik_2008.1
Thread model: posix
gcc version 3.4.3

Here is the subroutine file, run through the preprocessor using gcc-4.2.3:


-- 
           Summary: gcc 4.2.3 produces poor code compared to gcc-3.4.3 on
                    xeon prestonia
           Product: gcc
           Version: 4.2.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jeff at jeffunit dot com
 GCC build triplet: i586-manbo-linux-gnu
  GCC host triplet: i586-manbo-linux-gnu
GCC target triplet: i586-manbo-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36860