I'm seeing hundreds of warnings like this on a project that uses the idiom of 
self-registering objects.

It only happens if the constructor is a template.

This is a regression wrt previous gcc releases.

// Test case begins

class B {
public:
  B();  // Implemented elsewhere
};


class A {
public:
  template <typename T1>
  A(T1) {
    new B;
  }
};


A a(10);

// Test case ends

t:/sec/exp # g++ -c -Wall p.cpp 
p.cpp: In constructor `A::A(T1)':
p.cpp:11: warning: statement has no effect