There''s always the Dragon book. (Aho, Sethi and Ullman "Compilers Principles, Techniques and Tools" ISBN 0-201-10088-6 (This is the second edition, the first edition was just Aho and Ullman (And the scary thing is that I recommend this book so often, I have the ISBN memorized)))

And depending on your language features and the binding of variable x, x = x + 3 - 2 - (5 - 4) is just an ugly way to write x = x, which is not the same as nothing. (Memory mapped i/o, binding x to ports, volatile memory, etc.) It could be a complex way of setting back the timer by 18 clock cycles.

But anyway, the basic gist of reducing irresponsible statements like that, is you build a abstract syntax tree (I''ll represent mine in postfix, as the board can''t mangle that.)

x x 3 + 2 - 5 4 - - =

Then the AST under goes constant reduction. Arithmetic operations on pairs of constants are reduced. As well, operations of the form + 0 or * 1 are reduced out.

x x 3 + 2 - 1 - =

Another step of optimization is to regroup constants together using associativity and communitivity rules.

x x 3 2 - + 1 - =
x x 1 + 1 - =
x x 1 1 - + =
x x 0 + =
x x =

At this point the compiler can throw it out as a assignment to itself.