Return Statement in Scope with a function

Hi.


I'm writing a compiler which is a subset of C. I don't know how C
Compilers do this:


Example:


int fun(int b)
{


  if (b < 10)
  {
      return b;
  }
  else
  {
      b = 10;
  }
}


After the compilation of this program (supose you have the main()
function above), the error message is: "The function should have a
return value". The compiler is correct, because the "else" part
doesn't have a return statement... How the C (and many others)
Compilers do this?? In which phase of the compilation detect this
error. I think is in the Semantic checking... but I'm not sure
how.... Thanks in advance.
[It's very simple control flow analysis. The compiler notices that
the code at the end of the function isn't dead, i.e. there's a path to
it, which is a mistake in a non-void function. -John]

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