When I use gcc with -O1 optimization. Array data initialization is ignored and I end up with uninitialized data when I attempt to use the array

Using gcc 7.4.0 and compiling this sample program with the -O1 optimization flag, the data being set inside of the array 'cap' is being optimized out leaving me with uninitialized data.

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>

#define CAP_TYPE_1      0x0003
#define CAP_TYPE_2      0x0004
#define CAP_COUNT       2

#define CAP2_CIP_1      0x0001
#define CAP2_CIP_2      0x0002
#define CAP2_CIP_COUNT  2
static uint16_t cap_2_cips[CAP2_CIP_COUNT] = { CAP2_CIP_1, CAP2_CIP_2 };

#define CAP1_ALG_1      0x0010
#define CAP1_ALG_COUNT  1
static uint16_t cap_1_algs[CAP1_ALG_COUNT] =  { CAP1_ALG_1 };

typedef struct optests_cap_1
{
        uint16_t count;
        uint16_t len;
        uint16_t *alg;
        char     *buf;
} optests_cap_1_t;

typedef struct optests_cap_2
{
        uint16_t count;
        uint16_t *cip;
} optests_cap_2_t;

typedef struct optests_cap
{
        uint16_t type;
        uint16_t size;
        uint16_t flag;
        void     *data;
} optests_cap_t;

typedef struct optests_caps
{
        uint32_t count;
        optests_cap_t *structs;
} optests_caps_t;

static int populate_structs(optests_caps_t *caps)
{
        optests_cap_1_t *cap_1;
        optests_cap_2_t *cap_2;

        optests_cap_t cap[CAP_COUNT];

        cap_2 = (optests_cap_2_t*)malloc(sizeof(optests_cap_2_t));
        cap_2->count = CAP2_CIP_COUNT;
        cap_2->cip = cap_2_cips;

        cap[0].type = CAP_TYPE_2;
        cap[0].size = 6;
        cap[0].flag = 0;
        cap[0].data = cap_2;

        cap_1 = (optests_cap_1_t*)malloc(sizeof(optests_cap_1_t));
        cap_1->count = CAP1_ALG_COUNT;
        cap_1->len = 4;
        cap_1->alg = cap_1_algs;
        cap_1->buf = "ABCD";

        cap[1].type = CAP_TYPE_1;
        cap[1].size = 6 + cap_1->len;
        cap[1].flag = 42;
        cap[1].data = cap_1;

        caps->count = CAP_COUNT;
        caps->structs = cap;

        return 0;

}


int main(void)
{
        optests_caps_t caps;
        memset(&caps, 0, sizeof(optests_cap_t));

        populate_structs(&caps);

        printf("cap_count = %u\n", caps.count);
        for(int i = 0; i < caps.count; i++)
        {
                printf("Type: %u\n", caps.structs[i].type);
                printf("Size: %u\n", caps.structs[i].size);
                printf("Flag: %u\n", caps.structs[i].flag);
        }
        /* Free the memory */

}

Compile the code with:

gcc -O1 -o optest_O1 optest.c
gcc -O0 -o optest_O0 optest.c
gcc -o optest optest.c

The output is as such:

$ ./optest
cap_count = 2
Type: 4
Size: 6
Flag: 0
Type: 3
Size: 10
Flag: 42

$ ./optest_O0
cap_count = 2
Type: 4
Size: 6
Flag: 0
Type: 3
Size: 10
Flag: 42

$ ./optest_O1
cap_count = 2
Type: 2464
Size: 22561
Flag: 32596
Type: 2000
Size: 22624
Flag: 32596

Valgrind reports the following when running the optimized binary:

$ valgrind --tool=memcheck --leak-check=yes ./optest_O1

…

==7316== error calling PR_SET_PTRACER, vgdb might block
cap_count = 2
==7316== Use of uninitialised value of size 8
==7316==    at 0x4E9486B: _itoa_word (_itoa.c:179)
==7316==    by 0x4E97F0D: vfprintf (vfprintf.c:1642)
==7316==    by 0x4F6E2EB: __printf_chk (printf_chk.c:35)
==7316==    by 0x10871D: main (in /opttest/optest_O1)
==7316==
==7316== Conditional jump or move depends on uninitialised value(s)
==7316==    at 0x4E94875: _itoa_word (_itoa.c:179)
==7316==    by 0x4E97F0D: vfprintf (vfprintf.c:1642)
==7316==    by 0x4F6E2EB: __printf_chk (printf_chk.c:35)
==7316==    by 0x10871D: main (in /opttest/optest_O1)
==7316==
==7316== Conditional jump or move depends on uninitialised value(s)
==7316==    at 0x4E98014: vfprintf (vfprintf.c:1642)
==7316==    by 0x4F6E2EB: __printf_chk (printf_chk.c:35)
==7316==    by 0x10871D: main (in /opttest/optest_O1)
==7316==
==7316== Conditional jump or move depends on uninitialised value(s)
==7316==    at 0x4E98B4C: vfprintf (vfprintf.c:1642)
==7316==    by 0x4F6E2EB: __printf_chk (printf_chk.c:35)
==7316==    by 0x10871D: main (in /opttest/optest_O1)
==7316==
Type: 2464

…

if I use gcc -fno-tree-dce -fno-tree-dse flags along with -O1 I get the correct output. I would like to understand what GCC is doing, is it a gcc bug, or is there a different way to write the above code that would not trigger this issue?