FAQ 33.16 Can a programming languagerather than just the compileraffect the performance of software?

FAQ 33.16 Can a programming language rather than just the compiler affect the performance of software?

Yes.

Sometimes it is assumed that software performance is limited only by the compiler, not by the programming language. However, this is generally not the case. The efficiency of the executable is, at least in part, due to the language as well as the compiler. For example, compilers for dynamically typed OO languages cannot statically resolve member function invocations, because every member function is virtual and every object is passed by pointer. Therefore, every member function dispatch needs to go through the dynamic-binding mechanism, which generally costs a function call. Thus, a member function with 10 statements in many OO languages almost necessarily costs at least 10 function calls. The efficiency of the dynamic-binding mechanism can be improved, but it rarely can be improved enough to inline-expand these calls (a technique called customization can alleviate some of these issues in dynamically typed OO programming languages).

Languages such as C++ require the compiler to work harder, since not all member functions are necessarily virtual, and even if they are all virtual, not all objects are allocated from the heap. In addition, statically bound member functions can be expanded inline (see FAQ 13.01).