I tried to track down the bug mentioned previously in testing my
software SSE2 when compiled with -m64 and ended up removing all
of the CHECK and my own includes without eliminating the bug. The test
program works fine with -m32, or with -m64 -msse2, but it fails with
-m64 -mno-sse2. Here is the greatly reduced gccprob2.c:
8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<
#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);
}
8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<8<
Test runs:
% gcc -msse -mno-sse2 -m64 -o foo gccprob2.c
% ./foo #first value in s2 is wrong
s1 1.000000 2.000000
test s1 1.000000 2.000000
test s2 2.000000 2.000000
% gcc -msse -msse2 -m64 -o foo gccprob2.c
% ./foo
s1 1.000000 2.000000
test s1 1.000000 2.000000
test s2 1.000000 2.000000
% gcc -msse -mno-sse2 -lm -m32 -o foo gccprob2.c
% ./foo
s1 1.000000 2.000000
test s1 1.000000 2.000000
test s2 1.000000 2.000000
% gcc --version
gcc (GCC) 4.4.1
% 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
Is there something wrong with this program or is this a compiler bug?
Thanks,
David Mathog
[email protected]
Manager, Sequence Analysis Facility, Biology Division, Caltech
