[Bug c++/59874] New: Missing builtin (__builtin_clzs) when compiling with g++

[mikeb01 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59874

            Bug ID: 59874
           Summary: Missing builtin (__builtin_clzs) when compiling with
                    g++
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mikeb01 at gmail dot com

Created attachment 31888
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31888&action=edit
Preprocessed version of bug.cc

The following code:

#include <x86intrin.h>

int main(int argc, char** argv)
{
    return __lzcnt32(2047);
}

Fails to compile using g++ (works fine with gcc).  It will compile if the
-mlzcnt switch is used, but on some platforms that will generate incorrect
code.

The __builtin_clzs does not appear to be defined when using the c++ compiler. 
If I hand modify the lzcntintrin.h file and comment out the whole definition of
the __lzcnt16 intrinsic it works okay and generates the expected code.

$ g++ -v -save-temps -D__LZCNT__ bug.cc
Using built-in specs.
COLLECT_GCC=g++
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-4.8.2-20131212/obj-x86_64-redhat-linux/isl-install
--with-cloog=/builddir/build/BUILD/gcc-4.8.2-20131212/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 20131212 (Red Hat 4.8.2-7) (GCC) 
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-D' '__LZCNT__' '-shared-libgcc'
'-mtune=generic' '-march=x86-64'
 /usr/libexec/gcc/x86_64-redhat-linux/4.8.2/cc1plus -E -quiet -v -D_GNU_SOURCE
-D __LZCNT__ bug.cc -mtune=generic -march=x86-64 -fpch-preprocess -o bug.ii
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include-fixed"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../x86_64-redhat-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2

/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/x86_64-redhat-linux
 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/backward
 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/include
 /usr/local/include
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-D' '__LZCNT__' '-shared-libgcc'
'-mtune=generic' '-march=x86-64'
 /usr/libexec/gcc/x86_64-redhat-linux/4.8.2/cc1plus -fpreprocessed bug.ii
-quiet -dumpbase bug.cc -mtune=generic -march=x86-64 -auxbase bug -version -o
bug.s
GNU C++ (GCC) version 4.8.2 20131212 (Red Hat 4.8.2-7) (x86_64-redhat-linux)
    compiled by GNU C version 4.8.2 20131212 (Red Hat 4.8.2-7), GMP version
5.1.1, MPFR version 3.1.1, MPC version 1.0.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++ (GCC) version 4.8.2 20131212 (Red Hat 4.8.2-7) (x86_64-redhat-linux)
    compiled by GNU C version 4.8.2 20131212 (Red Hat 4.8.2-7), GMP version
5.1.1, MPFR version 3.1.1, MPC version 1.0.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 489f772b6d0264e1e4c03fca513f7a0d
In file included from
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include/immintrin.h:64:0,
                 from
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include/x86intrin.h:62,
                 from bug.cc:1:
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include/lzcntintrin.h: In function
‘short unsigned int __lzcnt16(short unsigned int)’:
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include/lzcntintrin.h:38:29: error:
‘__builtin_clzs’ was not declared in this scope
   return __builtin_clzs (__X);