```cpp
static void D() { }
static void Y() { D(); }
static void X() { Y(); }
static void C() { D(); X(); }
static void B() { C(); }
static void S() { D(); }
static void P() { S(); }
static void O() { P(); }
static void N() { O(); }
static void M() { N(); }
static void G() { M(); }
static void A() { B(); G(); }

int main() {
  A();
}
```
easy step:
```
$ clang++ -S -emit-llvm main1.cpp -o - | opt -analyze -dot-callgraph
$ dot -Tpng -ocallgraph.png callgraph.dot
```

filtered step:
```cpp
#include <vector>

struct A {
  A(int);
  void f(); // not defined, prevents inlining it!
};

int main() {
  std::vector<A> v;
  v.push_back(42);
  v[0].f();
}
```

two commands:
```
$ clang++ -S -emit-llvm main1.cpp -o - |
   opt -analyze -std-link-opts -dot-callgraph
$ cat callgraph.dot |
   c++filt |
   sed 's,>,\\>,g; s,-\\>,->,g; s,<,\\<,g' |
   gawk '/external node/{id=$1} $1 != id' |
   dot -Tpng -ocallgraph.png
```