Consider the following test case:

#define alignement 64

struct test {
public:
  int toto[100] __attribute__((aligned(alignement)));
};

int main () {
    test* t = new test();
    printf("%ld\n",(unsigned long)(&(t->toto[0])) % alignement);
    return 0;
}

This program typically prints a non-zero value, whereas customers would actually expect 0. This is due to default "new" (presumably doing malloc) only gurantees 16 byte alignment.

Compiler should detect when a default new operator is used to allocate unsufficiently aligned memory, and issue a relevent user diagnostics.

BTW, this issues can cause severe stability problems in AVX compilation, where 32-byte is the typical requirement for 256-bit AVX data types.