I wanted to use opt to get the control flow graph of a C code, using clang 18. It does not work, saying some issues with-opaque-pointers. Any idea?

root@2f18de92db5f:/# cat example.c
#include <stdio.h>

void foo(int n) {
    if (n > 0) {
        printf("Positiven");
    } else {
        printf("Non-positiven");
    }
}

int main() {
    foo(10);
    foo(-5);
    return 0;
}


root@2f18de92db5f:/# clang -S -emit-llvm example.c -o example.ll
root@2f18de92db5f:/# opt -dot-cfg example.ll
example.ll:12:17: warning: ptr type is only supported in -opaque-pointers mode
  store i32 %0, ptr %2, align 4
                ^
opt: example.ll:12:17: error: expected type
  store i32 %0, ptr %2, align 4