CSE443 Compilers. Dr. Carl Alphonce 343 Davis Hall

Transcription

1 CSE443 Compilers Dr. Carl Alphonce 343 Davis Hall

2 Phases of a compiler Target machine code generation Figure 1.6, page 5 of text

3 Plan for ROS M W F 5/1 5/3 5/5 Peephole optimization PROJECT Q's WW Misc. topics (not for project) PROJECT Q's 5/8 5/10 5/12 Misc. topics (not for project) PROJECT Q's WW Overview for Final Exam

4 KEIL update still pending Kris thinks the standard Cortex M7 set-up for Keil5 is incomplete. stay tuned

5 Final Exam 5/19/2017, Friday 8:00AM - 11:00AM Talbert 107

6 Project Due Date Question Would you prefer to have project due: Monday 5/15/2017 Tuesday 5/16/2017 Wednesday 5/17/2017 Thursday 5/18/2017 or Friday 5/19/2017

7 A few random optimizations Code motion Tail-call optimization Procedure in-lining

8 Code motion Observation: Loops are highly relevant for optimizations: their bodies are executed repeatedly Idea: move loop-invariant computation outside the loop body

9 Code motion Example [p. 592] while (i <= limit - 2) { If there is no change to limit in loop, then this is more efficient: t = limit - 2 while (i <= t) {

10 Tail-call optimization "A call f rom procedure f() to a procedure g() is a tail call if the only thing f() does, after g() returns to it, is itself return." Page 123 Advanced Compiler Design & Implementation Steven S. Muchnick

11 public class StackByCompositionWithArrayList<E> implements IStack<E> { private ArrayList<E> _front; public StackByCompositionWithArrayList() { _front = new public void push(e item) { _front.add(_front.size(), public E pop() { if (isempty()) { throw new EmptyStackException("Cannot pop an empty stack."); else { return public E peek() { if (isempty()) { throw new EmptyStackException("Cannot peek an empty stack."); else { return public boolean isempty() { return public String tostring() { return _front.tostring();

12 public class StackByCompositionWithArrayList<E> implements IStack<E> { private ArrayList<E> _front; public StackByCompositionWithArrayList() { _front = new public void push(e item) { _front.add(_front.size(), public E pop() { if (isempty()) { throw new EmptyStackException("Cannot pop an empty stack."); else { return public E peek() { if (isempty()) { throw new EmptyStackException("Cannot peek an empty stack."); else { return public boolean isempty() { return public String tostring() { return _front.tostring();

13 public class StackByCompositionWithArrayList<E> implements IStack<E> { private ArrayList<E> _front; public StackByCompositionWithArrayList() { _front = new public void push(e item) { _front.add(_front.size(), public E pop() { if (isempty()) { throw new EmptyStackException("Cannot pop an empty stack."); else { return public E peek() { if (isempty()) { throw new EmptyStackException("Cannot peek an empty stack."); else { return public boolean isempty() { return public String tostring() { return _front.tostring();

14 public class Model { public Model(String filename) { readdictionaryfromfile(filename); public void start() { notifyobservers(); public ArrayList<String> words() { return answer; private void initializegame() { _wordstofind.add(new Pair(target,false)); public void moveletterfrominventorytoguess(int index) { notifyobservers(); public void moveletterfromguesstoinventory(int index) { notifyobservers(); public boolean submit() { return false; public void clear() { notifyobservers(); public void shuffle() { notifyobservers(); private String chars2string(arraylist<character> list) { return s; public void addobserver(observer obs) { _observers.add(obs);

15 Tail-call optimization " all we really need to know about the callee is : 1. where it expects to find its parameters 2. where to branch to in order to begin executing its body, and 3. how large its stack frame is." [ibid., p. 464] ibid. is an "abbreviation of Latin ibidem in the same place. " [macos Dictionary, version 2.2.1]

16 Tail-call optimization A special case: tail recursion. Invocation record is reused. Recursive call is replaced by jump. Optimization transforms recursion with linear space needs into iteration with constant space needs.

17 Tail-call optimization fun fact(0) = 1 fact(n) = N * fact(n-1) vs fun factacc(0,acc) = Acc factacc(n,acc) = factacc(n-1,n*acc) fun fact(n) = factacc(n,1)

18 Procedure in-lining "Procedure integration, also called automatic inlining, replaces calls to procedures with copies of their bodies." [ibid., p 465] "The opportunity to optimize inlined procedure bodies can be especially valuable if it enables loop transformations that were originally inhibited by having procedure calls embedded in loops or if it turns a loop that calls a procedure, whose body is itself a loop, into a nested loop." [ibid., p 465]

19 Project questions?