CS255 Assignment #1 (LVN)

In this assignment, you are asked to implement local value numbering (LVN) and check for redundant expressions.

You are expected to handle commutativity for commutative operations. Recall that an operation is commutative if you can change the order of operands without changing the result. For example (+) is commutative but (-) is not. Your implementation must be able to assign the same value number to a+b and b+a.

As the final requirement, improve LVN by adding the Stewart extension. The Stewart extension improves LVN by identifying additional redundancy in the following example form.

a = b + c

d = a – b

Specifically, it guides LVN to assign the same value number to both (c) and (d). The idea of the solution was first raised by Chris Stewart when he was taking the class around 2004.  His idea was to insert additional value relations into the value number table. You should first work out this idea and make it concrete as an extension to the basic value numbering algorithm.

Note 1: You are expected to apply the Stewart extension on four operations: ‘+’, ‘-‘, ‘*’, and ‘/’.

Note 2: You should make sure that the Stewart extension can be applied on the following code as well.

a = b + c

e = a

d = e – b


To complete this assignment, take the following steps:

1. From Blackboard, download block.rb and vn_tests.rb to your project directory.

2. Implement the LVN class in the new file vn.rb.

4. Make sure all the tests in vn_tests.rb pass.

5. Document any test failures, if there is any, and explain why, in README.txt in plain text.

6. Extra credit.  In addition to finding the statements with a redundant expression, generate optimized code where all redundant expressions are removed.  Demonstrate the optimizer with a set of tests and put them in opt_tests.rb.  The tests should include all three tests in vn_tests.rb.

7. Submit your assignment on Blackboard. Make sure to include all the ruby files in your submission.

Due time: Friday Jan 29th at 23:59:59 EST.

Late submission policy: Each student can have a total of two days used for late submissions over all assignments . This means that if you submit the LVN assignment on Sunday, you will not be able to do any other late submission. But if you submit on Saturday, you still have one more day to use for one other assignment.

Policy on academic honesty :  Every line of code of the LVN analyzer and optimizer must be written by the student.  Do not copy code.  Do not show your LVN code to others until 2 days (48 hours) past the assignment due time.  The teaching staff is required to report every violation of the policy or suspicion of violation to the university’s Academic Honesty Board.  Contact the teaching staff if you have questions on the policy.


CS 255/455 Spring 2016


CSC 255/455 Software Analysis and Improvement (Spring 2016)

Lecture slides (when used), demonstration programs, and some of the reading material will be distributed through Blackboard.  Assignments and projects will be listed here.


  • def-use in URCC/LLVM
  • CFG pass in URCC/LLVM
  • Instruction counting in GCC/LLVM
  • Local value numbering
  • Trivia assignment.  Read slashdot.org for any current or archived posts.  Select any two posts on a topic of either GNU, GCC, or LVM (both posts may be on the same topic).  Read the posts and all discussions.  Write a summary with 200 or more words for each of the two posts.  In the summary, review facts and main opinions people agreed or disagreed.  Print and submit a paper copy Wednesday January 20th at the start of the class.  Then see me in one of my office hours for feedback on the summary.   There is no deadline for the meeting, but the grade is assigned only after the meeting.  If you see me before submitting the paper, bring your paper; otherwise, don’t since I’ll have your paper.

 Course description

With the increasing diversity and complexity of computers and their applications, the development of efficient, reliable software has become increasingly dependent on automatic support from compilers & other program analysis and translation tools. This course covers principal topics in understanding and transforming programs by the compiler and at run time. Specific techniques include data flow and dependence theories and analyses; type checking and program correctness, security, and verification; memory and cache management; static and dynamic program transformation; and performance analysis and modeling.

Course projects include the design and implementation of program analysis and improvement tools.  Meets jointly with CSC 255, an undergraduate-level course whose requirement includes a subset of topics and a simpler version of the project.


 Instructor and grading

Teaching staff: Chen Ding, Prof., CSB Rm 720, x51373; Rahman Lavaee, TA. CSB 630, x52569.

Lectures: Mondays and Wednesdays, 10:25am-11:40am, CSB 632

Office hours: Ding, Fridays 3:30pm-4:30pm (and Mondays the same time if pre-arranged);

TA Office hours: Wednesdays 3:30pm – 4:30pm, CSB 720.

Grading (total 100%)

  • midterm and final exams are 15% and 20% respectively
  • the projects total to 40% (LVN 5%, GCC/LLVM 5%, local opt 10%, global opt 10%, final phase 10%)
  • written assignments are 25% (trivial 1%; 3 assignments 8% each)

 Textbooks and other resources

Optimizing Compilers for Modern Architectures (UR access through books24x7), Randy Allen and Ken Kennedy, Morgan Kaufmann Publishers, 2001. Chapters 1, 2, 3, 7, 8, 9, 10, 11. lecture notes from Ken Kennedy. On-line Errata

Engineering a Compiler, (2nd edition preferred, 1st okay) Keith D. Cooper and Linda Torczon, Morgan Kaufmann Publishers. Chapters 1, 8, 9, 10, 12 and 13 (both editions). lecture notes and additional reading from Keith Cooper. On-line Errata

Workload Modeling for Computer Systems Performance Evaluation, Dror G. Feitelson, Cambridge University Press, 2014.   (book pdf for personal use)  Chapters 1, 3.1, 6.2