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Description of problem:
iterating over vector/table of bitfield structs and summing generates wrong sum(using sse2 instructions in -O3).

Version-Release number of selected component (if applicable):
RHEL6.5 gcc-4.4.7-4.el6.x86_64
RHEL5 gcc44-4.4.7-1.el5

How reproducible:
#include <stdio.h>
#include <stdint.h>

struct Bitf
{
    uint64_t begin  : 40;
    uint64_t len : 24;
};// __attribute__((packed));

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

    struct Bitf bf[10];
    uint64_t i;
    for(i = 0; i < 10; ++i)
    {
       struct Bitf b1 = {(1ULL << 40)-1, i};
       bf[i] = b1;
    }

    uint64_t rv = 0;
    struct Bitf * it;
    for(it = bf; it != (bf + 10); ++it)
    {
        rv += it->len;
    }
    printf("%llu\n",  rv);
}

Steps to Reproduce:
1. /usr/bin/gcc -o a1 a1.c -O3 -m64
2. ./a1

Actual results:
34225520685

Expected results:
45

Additional info:
-m32 -msse2 is buggy as well

-fno-tree-vectorize works this problem around

r157624 seems to fix it.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2015-1339.html