http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58928
chenjinzhi <gnome3fans at gmail dot com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |gnome3fans at gmail dot com --- Comment #1 from chenjinzhi <gnome3fans at gmail dot com> --- (In reply to Michael Barker from comment #0) > Created attachment 31113 [details] > Preprossed test.c code > > I have the following code: > > #include <stdint.h> > #include <stdio.h> > #include <x86intrin.h> > > long long lzcnt(long long l) > { > return __lzcnt64(l); > } > > int main(int argc, char** argv) > { > printf("%lld\n", lzcnt(atoll(argv[1]))); > return 0; > } > > If I compile and run with and without the -mlzcnt flag I get different > results: > > $ gcc src/test.c -D__LZCNT__ -mlzcnt && ./a.out 2047 > 10 > > $ gcc src/test.c -D__LZCNT__ && ./a.out 2047 > 53 > > $ gcc -v > Using built-in specs. > COLLECT_GCC=gcc > COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/lto-wrapper > Target: x86_64-redhat-linux > Configured with: ../configure --prefix=/usr --mandir=/usr/share/man > --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla > --enable-bootstrap --enable-shared --enable-threads=posix > --enable-checking=release --with-system-zlib --enable-__cxa_atexit > --disable-libunwind-exceptions --enable-gnu-unique-object > --enable-linker-build-id --with-linker-hash-style=gnu > --enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto > --enable-plugin --enable-initfini-array --enable-java-awt=gtk --disable-dssi > --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre > --enable-libgcj-multifile --enable-java-maintainer-mode > --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib > --with-isl=/builddir/build/BUILD/gcc-4.8.2-20131017/obj-x86_64-redhat-linux/ > isl-install > --with-cloog=/builddir/build/BUILD/gcc-4.8.2-20131017/obj-x86_64-redhat- > linux/cloog-install --with-tune=generic --with-arch_32=i686 > --build=x86_64-redhat-linux > Thread model: posix > gcc version 4.8.2 20131017 (Red Hat 4.8.2-1) (GCC) > > File test.i attached. It was the same for both compilations, so only one > file attached. I just test the code in my machine but the result is different from yours. I compile and run with and without the -mlzcnt flag and get the same result: 53. Here is my gcc -v output: Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/lto-wrapper Target: x86_64-redhat-linux Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-bootstrap --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-linker-hash-style=gnu --enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto --enable-plugin --enable-initfini-array --enable-java-awt=gtk --disable-dssi --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre --enable-libgcj-multifile --enable-java-maintainer-mode --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib --with-isl=/builddir/build/BUILD/gcc-4.8.2-20131017/obj-x86_64-redhat-linux/isl-install --with-cloog=/builddir/build/BUILD/gcc-4.8.2-20131017/obj-x86_64-redhat-linux/cloog-install --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux Thread model: posix gcc version 4.8.2 20131017 (Red Hat 4.8.2-1) (GCC) Hope helps