Project for CSC 255/455, Spring 2008


In the project, you will add your own optimization passes in the most recent Gnu C compiler, Gcc 4.2.2. Because Gcc is a real compiler, it is more difficult to use than the teaching compiler used in previous semesters. You have to know the basic framework of Gcc and how to manipulate the intermediate form, the gimple tree, for program analysis and transformation. This page includes many suggestions that will help you in the process. Please read the entire page and the page on source browsing and debugging before you start. Wish you a happy journey with Gcc.

Installation, compilation, and turn-in

  • Check out code and install: see Gcc-4.2.2 notes on installation
  • Use qsub -I at node64 to get a node to accelerate the make and install: see ClusterJobs
  • To prevent the problem of hardware incompatibility, you'd better build your compiler and use it and run the compiled executables on the same kind of machines.
  • Output gimple tree in c-like form: use option -fdump-tree-gimple
  • Invoke your pass: use -O2 -fcs255
  • Output gimple tree in c-like form after the pass for cs255: use option -fdump-cs255-tree-gimple
  • Use make for your testing: see An Example for Makefile
  • How to turn in your code: see Turn in for cs255

Browsing Gcc code and debugging

Other Gcc resources

Part 1: Trivial

In this part, you will add a pass that will insert code into a program to count and output the number of executed statements when the program executes. You need to first add a call at the beginning of the main function, which has a global counter initialized to 0; then add a call before each gimple statement, which increments the counter; and finally add a call at the exit, which reports the run-time instruction counts. The three functions are provided in cs255-lib.c:
  • Initialization: you'll need to add it at the entry of the main function
  • Increment: to be added before each real gimple statements (all except for labels)
  • Report: to be added at all possible exits of the program
  • Remember to add #include "cs255-lib.h" in your own testing programs.

This part should take at most tens of lines of code and no more than a day (including half an hour compiling the compiler for the first time). The purpose is to get you familiar with Gcc and the basic Gcc functions that you'll need for adding your optimization passes. In particular for this project, you will write the code in cs255.c at places tagged with string Do It Yourself. The code for counting the number of basic blocks and statements statically is already in the file. The code for getting the dynamic count of the basic blocks is also given.

Reading the relevant, existing code is the best way to help you writing your new code in an existing system. The next best way is to ask your instructor, TA, and your classmates to find out how to get Gcc to do something. You are encouraged to discuss the project and work out the algorithms on paper or a white or black board with others. The only limitation is that you should not copy other people's code---every line in your submitted code file must be yours.

This topic: Main > TWikiUsers > ChenDing > CS255Spring08 > ProjectHome
Topic revision: r15 - 2008-01-28 - XiaomingGu
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