• A compiler is simply a computer program that translates other computer programs to prepare them for execution. the output program is expressed in the operations available on some specific processor,
• A compiler often includes an optimizer that analyzes and rewrites that intermediate form.
• Compilers that target programming languages rather than the instruction set of a computer are often called source-to-source translators.
• A virtual machine is a simulator for some processor. It is an interpreter for that machine’s instruction set.
• Interpreters and compilers have much in common
  • Both analyze the input program and determine whether or not itis a valid program.
  • Both build an internal model of the structure and mean-ing of the program.
  • Both determine where to store values during execution.’
  • However, interpreting the code to produce a result is quite different from emitting a translated program that can be executed to produce the result.
• A good compiler contains a microcosm of computer science.
  • It makes practical use of greedy algorithms (register allocation),
  • heuristic search techniques(list scheduling),
  • graph algorithms (dead-code elimination), dynamic programming (instruction selection),
  • finite automata and push-down automata(scanning and parsing),
  • and fixed-point algorithms (data-flow analysis).
  • It deals with problems such as dynamic allocation, synchronization, naming, locality, memory hierarchy management,and pipeline scheduling.
• The Fundamental Principles of Compilation
  • The compiler must preserve the meaning of the program being compiled.
  • The compiler must improve the input program in some discernible way.