[Bug c++/27412] New: Incorrect result with sse intrinsic while extracting int

[Bug c++/27412] New: Incorrect result with sse intrinsic while extracting int

[gcc at povworld dot org]

Following code sets a 4 32-bit int sse vector to 1 for all elements and
extracts one int out of the vector. g++ returns an incorrect result when
compiling with -O2 or -O3 but not with -O1 or -O0

// -----------------------
#include <stdio.h>
#include <emmintrin.h>

int main() {

  __m128i ix = _mm_set1_epi32(1);               
  int res = ((int*)&ix)[1];
  printf("results: %i\n", res);

}
// -----------------------

compiled with:
$ g++-4.1.0 -O2 -msse2 

expected result: 1
actual result: -1209151480

similar misbehavior by gcc-3.4.5
acutal result: 134513897

$ g++-4.1.0 -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: /var/tmp/portage/gcc-4.1.0/work/gcc-4.1.0/configure
--prefix=/usr --bindir=/usr/i686-pc-linux-gnu/gcc-bin/4.1.0
--includedir=/usr/lib/gcc/i686-pc-linux-gnu/4.1.0/include
--datadir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.0
--mandir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.0/man
--infodir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.0/info
--with-gxx-include-dir=/usr/lib/gcc/i686-pc-linux-gnu/4.1.0/include/g++-v4
--host=i686-pc-linux-gnu --build=i686-pc-linux-gnu --disable-altivec
--enable-nls --without-included-gettext --with-system-zlib --disable-checking
--disable-werror --disable-libunwind-exceptions --disable-multilib
--disable-libmudflap --disable-libssp --enable-java-awt=gtk
--enable-languages=c,c++,java,fortran --enable-shared --enable-threads=posix
--enable-__cxa_atexit --enable-clocale=gnu
Thread model: posix
gcc version 4.1.0 (Gentoo 4.1.0)


-- 
           Summary: Incorrect result with sse intrinsic while extracting int
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: gcc at povworld dot org
  GCC host triplet: i686 linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27412

[Bug c++/27412] Incorrect result with sse intrinsic while extracting int

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-05-03 23:27 -------
You are violating C aliasing rules, use an union (which is non standard) or
memcpy.
  int res = ((int*)&ix)[1];

*** This bug has been marked as a duplicate of 21920 ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27412