[Bug c++/38525] sse2(int16) code fails with -O3

[leonid at volnitsky dot com]

------- Comment #7 from leonid at volnitsky dot com  2008-12-14 22:32 -------
(In reply to comment #2)
> ... please reduce your source to a
> short, self contained runtime testcase (in plain C if possible) that fails with
> certain compile flags.

I've tried to do that (see below).  But unfortunately it does not exhibit same
behavior. It will fail on any optimized compile with warning about aliasing.
Which is fixable by adding -fno-strict-aliasing. Don't know if this is related
on not. 

---------------------------------------------------------
#include <immintrin.h>
#include <stdio.h>

int main(int argc, char *argv[]) {

        int16_t  volatile A[2000];    
        for (int i=0; i<(2000-2); i+=2) { A[i]=1;  A[i+1]=2; };  A[333] = 3; 

         #define mk_m128i(x) *(__m128i*)&(x)
        __m128i m1 = mk_m128i(A[0]);
        __m128i m2 = mk_m128i(A[8]);

        for (int i= 16;  i < 2000-16; i+=16) {                  // SSE
                 m1 = _mm_max_epi16(m1, mk_m128i(A[i]) ); 
                 m2 = _mm_max_epi16(m2, mk_m128i(A[i+8]) ); 
        }  

        m1 = _mm_max_epi16(m1, m2);

        int16_t* ip  = (int16_t*)&m1;  
        printf("%hi %hi %hi %hi  %hi %hi %hi %hi \n", *ip++, *ip++, *ip++,
*ip++, *ip++, *ip++, *ip++, *ip);       

return 0;                                                                       
 }




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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38525