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List:       gcc-bugs
Subject:    [Bug c/37979]  New: GCC Overlooks Logical Operation Optimizations ?
From:       "engin at bzzzt dot biz" <gcc-bugzilla () gcc ! gnu ! org>
Date:       2008-10-31 12:02:36
Message-ID: bug-37979-16886 () http ! gcc ! gnu ! org/bugzilla/
[Download RAW message or body]

gcc looks like it's omitting a simple optimization which can be done on logical
operations.

/* Command line and output on a linux host */
engin@engin-desktop:~$ gcc -o test test.c -Os && ls -l test
-rwxr-xr-x 1 engin engin 6461 2008-10-31 12:26 test

engin@engin-desktop:~$ gcc -o test test.c -Os -DHAND_OPTIMIZED && ls -l test
-rwxr-xr-x 1 engin engin 6365 2008-10-31 12:26 test

engin@engin-desktop:~$ gcc -v
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v
--enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--with-gxx-include-dir=/usr/include/c++/4.2 --program-suffix=-4.2
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --enable-mpfr
--enable-targets=all --enable-checking=release --build=i486-linux-gnu
--host=i486-linux-gnu --target=i486-linux-gnu
Thread model: posix
gcc version 4.2.3 (Ubuntu 4.2.3-2ubuntu7

/* Command line and ouput on cygwin */

Engin@Engin-Dell /cygdrive/c/Users/Engin/Code/mmc
$ gcc -o test test.c -Os && ls -l test
-rwxr-xr-x 1 Engin None 9068 Oct 31 13:42 test

Engin@Engin-Dell /cygdrive/c/Users/Engin/Code/mmc
$ gcc -o test test.c -Os -DHAND_OPTIMIZED&& ls -l test
-rwxr-xr-x 1 Engin None 8556 Oct 31 13:43 test

Engin@Engin-Dell /cygdrive/c/Users/Engin/Code/mmc
$ gcc -v
Reading specs from /usr/lib/gcc/i686-pc-cygwin/3.4.4/specs
Configured with: /usr/build/package/orig/test.respin/gcc-3.4.4-3/configure
--verbose --prefix=/usr --exec-pref
ix=/usr --sysconfdir=/etc --libdir=/usr/lib --libexecdir=/usr/lib
--mandir=/usr/share/man --infodir=/usr/share
/info --enable-languages=c,ada,c++,d,f77,pascal,java,objc --enable-nls
--without-included-gettext --enable-ver
sion-specific-runtime-libs --without-x --enable-libgcj --disable-java-awt
--with-system-zlib --enable-interpre
ter --disable-libgcj-debug --enable-threads=posix --enable-java-gc=boehm
--disable-win32-registry --enable-sjl
j-exceptions --enable-hash-synchronization --enable-libstdcxx-debug
Thread model: posix
gcc version 3.4.4 (cygming special, gdc 0.12, using dmd 0.125)


/************* CODE ******************/
volatile int* foo = (volatile int*)0x23232322;


int
main(void)
{
        int a, b, c, d, e, f, g, h, z = 0;
        a = *foo;
        b = *foo;
        c = *foo;
        d = *foo;
        e = *foo;
        f = *foo;
        g = *foo;
        h = *foo;

#ifndef HAND_OPTIMIZED

        if ( 
                (f && c && b && a) || 
                (f && e && d && a) || 
                (f && e && h && a) || 
                (g && c && b && a) || 
                (g && e && d && a) || 
                (g && e && h && a) 
           )
#else
        if ((f||g) && a && ( (b&&c) || ((d||h)&& e)))
#endif
        {
                z= a + b + c;
                h=12;  
                d= h + b + c;
                e=45;  
        }


        e=z*2+d+a;
        *foo = e;

        while(1)
        {
                *foo = e;
        }

}


-- 
           Summary: GCC Overlooks Logical Operation Optimizations ?
           Product: gcc
           Version: 4.2.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: engin at bzzzt dot biz


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37979

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