clang UBSan test case fails at -O1 and above

gistfile1.txt

#include <string>

struct obj1_t
{
    std::string text;
    int val;
};

struct obj2_t
{
    int val;
    char padding[16];
};

struct obj3_t
{
    int field1;
    int field2;
    long long aligner;

    void func(obj2_t obj2, int param, ...)
    {
        this->field1 = true;
        if (param && this->field2)
        {
            obj1_t obj1;
            obj1.val = obj2.val;
        }
    }
};



int main(void)
{
    obj2_t obj;
    obj3_t p;
    p.func(obj, 0);
    return 0;
}