[Bug c/64185] New: Optimized code gives unexpected results

[zaz at ua7 dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64185

            Bug ID: 64185
           Summary: Optimized code gives unexpected results
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zaz at ua7 dot net

Created attachment 34191
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34191&action=edit
Test code for reproduce problem

Hello 
I found a open-source SIP library sofia-sip-ua work incorrect with GCC 4.7.3
and above. For me it looks like GCC optimization/compilation issue. I have
reproduce some problem on small test application (full code in attachment):

#include <stdio.h>

struct kv_s
{
    int k;
    int v;
};
typedef struct kv_s kv_t;

struct dict_s
{
    kv_t kv1[1];
    kv_t kv2[1];
    kv_t kv3[1];
    kv_t kv4[1];
    kv_t kv5[1];
    kv_t kv6[1];
    kv_t kv7[1];
    kv_t kv8[1];
};
typedef struct dict_s dict_t;

void initDict(dict_t *dict)
{
    dict->kv1[0].k =  1;
    dict->kv1[0].v = -1;

    dict->kv2[0].k =  2;
    dict->kv2[0].v = -2;

    dict->kv3[0].k =  3;
    dict->kv3[0].v = -3;

    dict->kv4[0].k =  4;
    dict->kv4[0].v = -4;

    dict->kv5[0].k =  5;
    dict->kv5[0].v = -5;

    dict->kv6[0].k =  6;
    dict->kv6[0].v = -6;

    dict->kv7[0].k =  7;
    dict->kv7[0].v = -7;

    dict->kv8[0].k =  8;
    dict->kv8[0].v = -8;
}

int searchDict1(dict_t *dict, int key)
{
    int i;
    kv_t *kvs = dict->kv1;
    for(i=0; i<=6; i++)
    {
        if(key == kvs[i].k)
        {
            return kvs[i].v;
        }
    }

    return 0;
}


int searchDict2(dict_t *dict, int key)
{
    int i;
    for(i=0; i<=6; i++)
    {
        if(key == dict->kv1[i].k)
        {
            return dict->kv1[i].v;
        }
    }

    return 0;
}

int main(int argc, const char* argv[])
{
    dict_t dict;
    int res;

    initDict( &dict );

    res = searchDict1(&dict, 4);
    printf("Found1 %i\n", res);

    res = searchDict2(&dict, 4);
    printf("Found2 %i\n", res);

    return 0;
}

Expected otput of this application:
Found1 -4
Found2 -4

But I see next:
$ gcc --version
gcc (Gentoo 4.8.3 p1.1, pie-0.5.9) 4.8.3

$ gcc -O0 -Wall ./test.c -o test-O0 && ./test-O0
Found1 -4
Found2 -4

$ gcc -O2 -Wall ./test.c -o test-O2 && ./test-O2
Found1 -4
Bus error

$ gcc -O2 -fno-aggressive-loop-optimizations -Wall ./test.c -o test-O2-nalo &&
./test-O2-nalo
Found1 -4
Found2 -1

I got similar results on GCC: 4.7.3, 4.8.3 and 4.92

Looks like I reproduced 2 different problems:
1) "Loops do not terminate" which is posted as know issue on
https://gcc.gnu.org/bugs/
2) Something new when build with "-O2 -fno-aggressive-loop-optimizations", code
found incorrect entry.

I agree code looks not clean when I try access a array out of bunds, but a
looks applications use "hack" like this. For my opinion there possible next
solutions for this issue:
1) searchDict2 will return same response as searchDict1 independent of
optimizations.
2) Provide some command line option (like -fno-aggressive-loop-optimizations)
so with this new option + -fno-aggressive-loop-optimizations it work in same
way as searchDict1.
3) Produce a WARNINGS during compilation (if -Wall specify) about possible
logic corrupt during optimizations.

Best Regards
Alex