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From: "mathog at caltech dot edu" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c/46716] New: bad code generated with -mno-sse2 -m64
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46716

           Summary: bad code generated with -mno-sse2 -m64
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: mathog@caltech.edu


The following small program generates incorrect output when compiled with
the flags -mno-sse2 -m64 on a 64 bit system.  Output is correct for -m32
or -msse2 -m64.  The problem manifests as the lower double of the second
parameter passed into test() being replaced by the value of the second double
from the first parameter.

% cat /etc/release
Mandriva Linux release 2010.0 (Official) for x86_64
% cat /proc/cpuinfo | head -10
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 33
model name      : Dual Core AMD Opteron(tm) Processor 280
stepping        : 2
cpu MHz         : 1000.000
cache size      : 1024 KB
physical id     : 0
siblings        : 2
% gcc --version
gcc (GCC) 4.4.1

example:

% gcc -msse -mno-sse2 -I. -m64   -o foo gccprob2.c
% ./foo
s1      1.000000 2.000000
test s1 1.000000 2.000000
test s2 2.000000 2.000000
% gcc -msse -mno-sse2 -I. -m32   -o foo gccprob2.c
OR
% gcc -msse -msse2 -I. -m64   -o foo gccprob2.c
s1      1.000000 2.000000
test s1 1.000000 2.000000
test s2 1.000000 2.000000

*************************************************
#include <stdio.h> /* for printf */
typedef double    __m128d __attribute__ ((__vector_size__ (16),
__may_alias__));
typedef union
{
  __m128d x;
  double a[2];
} union128d;
#define EMM_FLT8(a)    ((double *)&(a))

void test ( __m128d s1, __m128d s2)
{
printf("test s1 %lf %lf\n",EMM_FLT8(s1)[0],EMM_FLT8(s1)[1]);
printf("test s2 %lf %lf\n",EMM_FLT8(s2)[0],EMM_FLT8(s2)[1]);
}

int main (void)
{
__attribute__ ((aligned (16)))  union128d s1;
  s1.a[0] = 1.0;
  s1.a[1] = 2.0;
printf("s1      %lf %lf\n",s1.a[0],s1.a[1]);
  test (s1.x, s1.x);
}
**************************************************