Compiling “premature optimization is the root of all evil.” -Donald Knuth

Optimization In LISP, you can write slow code fast or fast code slow Experience will help you overcome common pitfalls (over use of append in recursive algorithms for example) In general, worry about the top level algorithms first. You can always speed it up later

Compiling LISP can be compiled into machine code just like other languages – Typically results in a drastic speed up for LISP programs Compilation can reduce both running time and memory consumption

Time a Function You can see how long it takes to evaluate a function by wrapping the function call in a call to time (defun waste-time (n) (dotimes (i n) (* i i))) >(time (waste-time 50000)) real time : secs run-gbc time : secs child run time : secs gbc time : secs NIL

Compile >(time (waste-time )) real time : secs run-gbc time : secs child run time : secs gbc time : secs NIL >(compile 'waste-time) […Compiler output…] >(time (waste-time )) real time : secs run-gbc time : secs child run time : secs gbc time : secs NIL

Disassemble We can look at the assembly code produced by compile using disassemble System and implementation dependent Here’s an example in CLISP >(defun add1 (n) (1+ n)) ADD1 >(disassemble 'add1) Disassembly of function ADD1 1 required argument 0 optional arguments No rest parameter No keyword parameters 3 byte-code instructions: 0 (LOAD&PUSH 1) 1 (CALLS2 151) ; 1+ 3 (SKIP&RET 2) NIL GCL output can be a mess since it actually transforms LISP into C code

Compile-File You can also compile all functions in a given file (compile-file "file.lisp") To run functions from the compiled file, load it like any other file (load "file.fas") The specific file extension depends on implementation

Inlining You can make a function be an inline function by using declare (defun f (x) (* x x)) (defun g (x) (declare (inline f)) (+ (f x) (f x))) Now, upon compiling g, the actual body of f will be copied into g in the pertinent locations, though only within g. To make f be an inline function everywhere, use declaim instead of declare, within the global scope. Cannot be used with recursive functions

More Type Safety declare and declaim can specify other compiler directives You can use to streamline compiled functions to only expect certain types using type >(defun f (x y) (declare (type integer x y)) (+ x y)) F >(f ) 9.0 >(compile 'f) …Compiler output… >(f 3 4) 7 >(f ) Error

Optimizing The optimize declaration allows several optimization priorities to be set Priorities are on a scale from 0 to 3, with 3 the most important – compilation-speed : speed of the compilation process – debug : ease of debugging – safety : run-time error checking – space : both code size and run-time space – speed : speed of the object code Example specification (defun f (x y) (declare (optimize (safety 2) (speed 3))) (+ x y))