Specialization is used where a variable is known to often hold one particular value. In this case, it is possible to generate code taking advantage of this constant value, e.g. not passing a parameter, using immediate addressing modes, eliminating the evaulation of an if-then-else statement and one of the clauses, (either the then or else clauses) etc. For example, if you have code like
  if (extendedBehavior)
    x = 11;
and extendedBehavior is often false, then you can specialize the above code to just "x=11;". Usually, the assumption can't be proved (e.g. that extendedBehavior is false), so the specialized code has to be protected by a guard, which essentially says "if extendedBehavior is true, branch to the non specialized code; else branch to the specialized code".

Under appropriate circumstances, the performance gain from specialization can be quite considerable.

See also PartialEvaluation, ProgramSpecialization (a synonym for PartialEvaluation).

-- MikeVanEmmerik - 03 Dec 2001

Revision: r1.1 - 03 Dec 2001 - 06:35 - MikeVanEmmerik
Transform > ProgramOptimization > ProgramSpecialization
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