Getting It Right COMS W4115 Prof Stephen A Edwards Fall 2006 Columbia University Department of Computer Science Getting It Right Your compiler is a large software system developed by four people How do you get it right Subjects Team oriented development Interface oriented design Version control systems assert Regression test suites Writing tests Code coverage Makefiles Team oriented Development Basic challenge Remove as many inter person dependencies as possible One group asked if the lexer parser person should finish before the tree walker person started Divide and conquer try to make it so that each person can work at his her own rate and not depend on others Tricky each pass depends on the previous one Solution careful design and modularity Interface oriented Development Divide your compiler into a series of modules e g 1 Lexer Parser 2 Static semantics 3 Code generation 4 Assembler Clearly define the interface between each module You ll want to write this in your project report anyway Make the interfaces the contracts between the team members Interface oriented design Write the interfaces first Document them well Write the public class definition the method declarations and the comments first Later fill in code for each method private fields etc Use javadoc to extract documentation from your Java code and share with other group members Version Control Systems Four people working on a single program is not as easy as just one Need some way to make sure everybody s working on the same program Version control systems a good solution The CVS Version Control System Basic model Grammar g v Repository Main java v Makefile v Grammar g Parser java Alice s Lexer java working Main java directory Main class Makefile Grammar g Bob s Main java working Main class directory Makefile Using the CVS Version Control System 1 Prepare a repository 2 Add an empty sudirectory to the repository 3 Create a working directory 4 Add files update directory commit changes One group member does 1 2 once Each group member does 3 once Each group member does 4 repeatedly Using CVS Creating a working directory mkdir mydir cd mydir cvs checkout ourproj Editing adding and updating cd ourproj edit files compile etc cvs add Grammar g cvs commit Grammar g cvs update Assert class Foo public static void main String args assert false javac source 1 4 foo java java ea Foo Exception in thread main java lang AssertionError at Foo main foo java 3 Assert Philosophy Catch errors early and often Check function arguments are acceptable E g assert n null Check function return value is consistent Check constructor has filled in every field Check object state is consistent Check loop invariants For the really ambitious write methods that check consistency of a whole data structure Regression test suites How to avoid introducing new bugs when adding features Partial answer build something that tells you whether you ve broken the program Regression suite collection of tests exercises as much of your program as possible results are compared with golden references Regression tests Easiest is when program takes a text file as input and produces text as output Fortunately compilers behave like this Regression test inputs short programs Regression test golden references assembly language Example tests module test emit1 type a type b input a input b integer output c integer emit a emit b emit c end module module output output output test emit2 a b integer c float emit a emit b 10 emit c 5 0f end module Writing Tests Try to cover as much of your language as possible Try to write one test for each feature mentioned in the language reference manual Build sequences of tests that start with simple versions of a feature and build into the most complex Keep tests focused easier to track down fault if one fails Running Tests Easiest is to use a scripting language that invokes the test compares the outputs and logs results and any errors For CEC I wrote a shell script to do this Shell Script Carefully runs two programs Compares output to reference file Stores results when it differs bin sh STRLXML strlxml XMLSTRL xmlstrl globallog teststrlxml log rm f globallog error 0 Shell Script Check basename echo 1 sed s s strl reffile echo 1 sed s strl out xmlfile basename xml outfile basename out difffile basename diff echo n Parsing basename echo Parsing basename 1 2 STRLXML 1 xmlfile 2 1 echo FAILED strlxml terminated error 1 return 1 XMLSTRL xmlfile outfile 2 1 echo FAILED xmlstrl terminated error 1 return 1 Shell Script diff b reffile outfile difffile 2 1 echo FAILED output mismatch error 1 return 1 rm xmlfile outfile difffile echo OK for file in tests test strl do Check file 2 globallog done exit error Code coverage Basic idea your test suite should at least send the program counter over every part of your code To measure coverage need some sort of tool that can tell when each line of code is executed I found a couple of them gcov works with gcc to report for C C clover Commercial tool for Java but free for students and open source developers There are many more Example of gcov gcc fprofile arcs ftest coverage tmp c a out gcov tmp c 87 50 of 8 source lines executed in file tmp c Creating tmp c gcov 1 1 11 10 1 1 1 main int i total total 0 for i 0 i 10 i total i if total 45 printf Failure n else printf Success n Makefiles How do you make it easy to compile your compiler Need to run ANTLR to generate files then run javac on the results How do you make sure everything gets compiled when needed A Basic Makefile cat Makefile Simp class Simp java javac Simp java make Simp class javac Simp java make Simp class make Simp class is up to date A More Complicated Makefile JAVASRC SimpParser java SimpWalker java SimpLexer java SimpParserTokenTypes java SimpParser class JAVASRC javac JAVASRC SimpParser java SimpLexer java Simp g java antlr Tool Simp g clean rm f class SimpParserTokenTypes txt SimpParser java SimpWalker java SimpLexer java SimpParserTokenTypes java A More Complicated Makefile make java antlr Tool Simp g ANTLR Parser Generator Version 2 7 1 1989 2000 jGu javac SimpParser java SimpWalker java SimpLexer java S rm SimpParser class make javac SimpParser java SimpWalker java SimpLexer java SimpParserTokenTypes java make clean rm f class SimpParserTokenTypes txt SimpParser java SimpWalker java SimpLexer java SimpParserTokenTypes java Writing Makefiles Rules take the form target source source commands z tab Variable definition and use variable value
View Full Document
Unlocking...