What kind of dead code can GCC eliminate from the final output?

I have always been told that compiler is sufficient smart to eliminate dead code. Much of the code that I am writing has a lot of information known at compile time but the code has to be written in most generic form. I don't know any assembly so I cannot examine the generated assembly. What kind of code that can be effectively eliminated in the final executable?

Few examples but not limited to

f(bool b){
 if(b){
  //some code
 }else{
  //some code
 }
}
f(true);
//////////////////////////
template<bool b>
f(){
 if(b){
  //some code
 }else{
  //some code
 }
}
f<true>();
///////////////////////////

What if definition of f is in other objective code and the the called f(true) is in main. Will link time optimisation effectively eliminate the dead code? What is the coding style/compiler option/trick to facilitate dead code elimination?