[Bug c/54743] New: Large loop runs endingless

[slbyan at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54743



             Bug #: 54743

           Summary: Large loop runs endingless

    Classification: Unclassified

           Product: gcc

           Version: 4.6.3

            Status: UNCONFIRMED

          Severity: normal

          Priority: P3

         Component: c

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: slb...@gmail.com





When the loops is 1000000000, the -O3 or -O2 -funroll-loops make the code runs

fast enough(~17sec, on Intel(R) Core(TM)2 Duo CPU E7400 @ 2.80GHz), and when

double the loops (2000000000), the time doubles as expected. However, when

loops is 3000000000, the code runs hours without ending.

The code is:



#include <stdio.h>

static long double vec_a[16] ={

    1.0,2.0,3.0,4.0,

    11.0,22.0,33.0,44.0,

    111.0,222.0,333.0,444.0,

    1111.0,2222.0,3333.0,4444.0};

static long double vec_b[16] ={

    1.0,2.0,3.0,4.0,

    11.0,22.0,33.0,44.0,

    111.0,222.0,333.0,444.0,

    1111.0,2222.0,3333.0,4444.0};

static long MAX = 3000000000L;

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

    long double c = 0.0f;

    for (int i=0; i < MAX; ++i)

        for (int j=0; j<16;++j)

            c += vec_a[j]* vec_a[j];

    printf("%llf\n",c);

    return 0;

}