1. Advanced Compiler Design An Introduction to the Javali Compiler Framework Zoltán Majó 1

2. Javali  Simple object-oriented programming language  Your tasks in this lecture are:  Implement an SSA-based IR  Implement some compiler optimizations  Come up with your own project ... and you have to do all this for Javali 2

3. Javali  You may build your own Javali compiler  We provide a framework that already implements  Parsing  IR  Code generation  Semantic checking  You can extend the framework 3

4. Outline  Building the Control Flow Graph (CFG)  Debugging & Testing 4

5. class Main { void main() { int count, i, zeros, notZeros; count = read(); i = 0; zeros = 0; notZeros = 0; while (i < count) { input = read(); if (input == 0) { zeros++; } else { notZeros++; } i++; } write(zeros); write(notZeros); } } 5 Example: counting # of zero/non-zero elements Program code

6. class Main { void main() { int count, i, zeros, notZeros; count = read(); i = 0; zeros = 0; notZeros = 0; while (i < count) { input = read(); if (input == 0) { zeros++; } else { notZeros++; } i++; } write(zeros); write(notZeros); } 6 Constructing the Control Flow Graph BB1 count = read(); i = 0; zeros = 0; notZeros = 0; BB7 write(zeros); write(notZeros); BB6 i++; true false Program codeControl Flow Graph BB4 zeros++; BB5 notZeros++; true false BB3 input = read(); COND(input == 0) BB2 COND(i < count)

7. class Main { void main() { int count, i, zeros, notZeros; count = read(); i = 0; zeros = 0; notZeros = 0; while (i < count) { input = read(); if (input == 0) { zeros++; } else { notZeros++; } i++; } write(zeros); write(notZeros); } 7 Implementing CFG Construction Program codeAbstract Syntax Tree Assign Var::countBuiltInRead WhileLoop BinaryOp::< Var::iVar::count Seq Assign Var::inputBuiltInRead...

8.  Simple idea: for each method of the program { walk through the method’s list of AST nodes add each AST node to the current basic block }  More action required: IfElse and WhileLoop AST nodes  Create new basic blocks if necessary  Connect new basic blocks to existing ones so that connections reflect the method’s control flow  Not allowed in the CFG: IfElse and WhileLoop AST nodes  Use Visitor pattern to traverse AST: extend AstVisitor  Add all this functionality to CFGBuilder.build() 8 Implementing CFG Construction

9. Debugging  In debug mode compiler dumps CFG into a *cfg.dot file  Use dotty from the Graphviz package to visualize CFG 9 Testing  Example programs included in the javali_tests directory  Get reference CFG generated by our server: run TestSamplePrograms as JUnit test

10. Thanks! Questions? Get fragment from: https://svn.inf.ethz.ch/svn/trg/cd_students/2012ss/teams/ /CD2_A0/ 10