: Advanced Compiler Design

Transcription

1 : Advanced Compiler Design Thomas R. Gross Computer Science Department ETH Zurich, Switzerland

2 Topics Program opgmizagon Op%miza%on Op%mize for (execu%on) speed Op%mize for (code) size Op%mize for energy consump%on Program analysis Program transformagon Compiler engineering Compile %me vs. code quality 3

3 Topics -- congnued Ahead-of-Gme compilers Just-in-Gme compilers Mul%-%er compila%on systems Binary translators Special purpose compilers Source language(s): imperagve, stagcally typed objectoriented (class-based) programming languages Excursions to other language worlds 4

4 LogisGcs Lectures Wednesday Friday 9-10 RecitaGons Friday Place: CAB G 51 Web site migragng to new ETH Corporate Design not up to date for now 5

5 Learning by doing Lectures present concepts, algorithms, tradeoffs RecitaGons repeat, provide context Course credit given if you Do homework Homework (3 planed) 40% of the grade Develop and present a (compiler) project 60% of the grade Homework and projects done in teams of 2 students 7

6 Homework Build/extend a compiler Focus on program opgmizagon Prepara%on for project Homework: build compiler infrastructure, implement opgmizagons Project: define and invesggate a compiler quesgon 8

7 Learning by doing The work you turn in must be your work. You must review your partner s work Turning in the work of others is cheagng. ETH has a set of rules that you should know. Bo^om line: do not copy a design or code (or text ) without proper a^ribugon. In papers or a report you must iden%fy and cite work not performed by you. For programs, you must iden%fy your source(s) A]ribu%on must be clearly visible Code reuse is fine but not presen%ng the work of others as your work Talk to the instructor/ta if necessary 9

8 Homework Both members of a team must contribute Both of you are responsible for the solu%on you turn in We reserve the right to ask ques%ons about the design, implementa%on, tes%ng plan, etc. You must turn in your own work. Finding a solu%on in a someone else s directory is chea.ng. ETH has a policy on chea%ng. 10

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11 Discussion John and Jane form team Y and they work on homework N. They decide that Jane should implement the (joint) design, John will work more on a future homework. As Jane starts working on the implementa@on, she realizes that team X messed up the protec@on of the svn directory and she copies a snapshot. She improves it a liele (beeer documenta@on, re-arrangment of methods, etc) and turns in the solu@on. The TA detects that team Y copied from team X; Jane admits her mistake, and the case is forwarded to the Rector. Ques@on: Is John a guilty party (as defined by ETH regula@ons)? Discuss this ques@on with your neighbor. 13

12 Homework We do not want to play police. Do the homework yourself. Discussions are fine (and encouraged) copying code is not. 14

13 RecitaGons Review material, introduce framework, etc. MeeGngs when announced in class May swap lectures and recitagons on Friday Esp. early in semester Cover material for later projects Friday is not op.onal 15

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15 1.0 IntroducGon Central topic: opgmizagon techniques for modern programming languages Key issues for real compilers Techniques have many uses OpGmizaGon resulgng code is rarely opgmal Oden impossible to prove op%mality May have proofs for an abstract execu%on engine (virtual machine) but %e to real systems difficult Interested in improvement be]er than naïve transla%on pre]y good incremental transforma%ons 18

16 1.1 Intermediate representagon IR (Intermediate representagon): output of front-end, input to backend OpGmizer IR à IR Or separate IRs: IR1 and IR2 (or high-level IR, low-level IR) 19

17 IR concerns Abstract from unnecessary features of programming language Support mul%ple front-ends Decouple front-end and back-end Mul%ple back-ends Keep essengal informagon Structure Types Expose operagons 20

18 Simple compiler: Tree-based IR One assignment stmt: one binary tree int A, B, C, D; A = B + C * D; A tree has a root Top node Right and led subtrees Sequences of statements: forest of trees 21

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22 Assessment of trees Simple Not a good IR for opgmizagon No reuse of values Values flow through designated variables Overspecifica%on Global aspects (e.g., last writer for a variable) hidden 30

23 1.2 Requirements for IR Make data dependences explicit Capture producer consumer rela%onship Make control dependences explicit Determine essen%al order of execu%on that must be honored 31

24 Control dependence Captures if execugon of one { statement block funcgon call } depends on the statement execugon of some other { block } funcgon call 32

25 Requirements for IR Make data dependences explicit Capture producer consumer rela%onship Make control dependences explicit Determine essen%al order of execu%on that must be honored Ideally the IR contains only true (essengal) constraints No superfluous constraints 33

26 IR (& language) restricgons No mulg-threading Single thread no changes outside of control of this func%on/program No aliasing of method-local variables Variables in heap may be aliased but restric%ons may apply E.g., references can only refer to objects/arrays but not to fields/elements Focus first on method-local scalar variables Important group: includes compiler-generated temporary variables for address arithme%c 34

27 Control dependence graph CDG (control dependence graph) captures control dependences Nodes: basic blocks (BB) Edges: possible control transfers A basic block is a maximal sequence of statements that are always executed together Unless there is an excep%on these are usually handled differently 35

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30 IR concerns Make data dependences explicit Capture producer consumer rela%onship // 1 // x = a + b ; // other basic blocks // // 2 // d = x + 1; // 3 // b = a + c; x produced by 1, consumed by 2 b in 1 must be read before b is wri^en in 3 40

31 Simple solugon: execute 1, 2, and 3 in order What ma^ers is 1 reads the old value and 3 produces a new value Idea: rename variable and/or make copies // 1 // x = a + foo ; // 2 // d = x + 1; // 3 // bar = a + c; 43

32 Compiler introduces a new name whenever a new value is produced. Could use any name but usually use subscripts: b 1, b 2, // 1 // x = a + b 34 ; // 2 // d = x + 1; // 3 // b 56 = a + c; IR used in opgmizing compilers: stagc single assignment (SSA) 44