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. Below is a quote from Will Durant from his 1926 book The story of philosophy

"Happiness, says an old lesson, lies rather in achievement than in possession or satiation. The healthy man asks not so much for happiness as for an opportunity to exercise his capacities; and if he must pay the penalty of pain for this freedom and this power he makes the forfeit cheerfully; it is not too great a price. We need resistance to raise us, as it raises the airplane or the bird; we need obstacles against which to sharpen our strength and stimulate our growth. Life without tragedy would be unworthy of a man."

Installation, compilation, and turn-in

  • Check out code and install: See Gcc-4.0.1 notes on installation and change all 4.0.1 to 4.2.2.
  • For those who have no access to department research network, please download gcc-4.2.2.tar.bz2 and unzip it with the command tar -jxvf gcc-4.2.2.tar.bz2.
  • 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. 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.

For testing, there are some open test cases. You may use the results from them to check your code with your classmates. And they are very useful in following parts and final competition.

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Topic revision: r18 - 2008-01-30 - ChenDing
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