Alive 2 Part 1: Introduction

[This piece is co-authored by Nuno P. Lopes and John Regehr.] Compiler bugs threaten the correctness of almost any computer system that uses compiled code. Translation validation is a path towards reliably correct compilation that works by checking that an individual execution of the compiler did the right thing. We created a tool, Alive2, that […]

Precision Opportunities for Demanded Bits in LLVM

[Although this post was written to stand by itself, it builds on the previous one. It is authored by Jubi Taneja, Zhengyang Liu, and John Regehr.] When designing computer systems, it can be useful to avoid specifying behaviors too tightly. For example, we might specify that a math library function only needs to return a […]

Testing Dataflow Analyses for Precision and Soundness

[This piece is co-authored by Jubi Taneja, Zhengyang Liu, and John Regehr; it’s a summary of some of the findings from a paper that we just recently completed the camera ready copy for, that is going to be published at CGO (Code Generation and Optimization) 2020.] Update from Jan 12 2020: Looks like there’s a […]

Helping Generative Fuzzers Avoid Looking Only Where the Light is Good, Part 1

Let’s take a second to recall this old joke: A policeman sees a drunk man searching for something under a streetlight and asks what the drunk has lost. He says he lost his keys and they both look under the streetlight together. After a few minutes the policeman asks if he is sure he lost […]

Design and Evolution of C-Reduce (Part 2)

Part 1 of this series introduced C-Reduce and showed how it combines a domain-independent core with a large collection of domain-specific passes in order to create a highly effective test-case reducer for C and C++ code. This part tells the rest of the story and concludes. Parallel Test-Case Reduction C-Reduce’s second research contribution is to […]

Design and Evolution of C-Reduce (Part 1)

[This piece is posted in parallel on the IEEE Software blog. Karim Ali copyedited.] Since 2008, my colleagues and I have developed and maintained C-Reduce, a tool for programmatically reducing the size of C and C++ files that trigger compiler bugs. C-Reduce also usually does a credible job reducing test cases in languages other than […]

It’s Time for a Modern Synthesis Kernel

Alexia Massalin’s 1992 PhD thesis has long been one of my favorites. It promotes the view that operating systems can be much more efficient than then-current operating systems via runtime code generation, lock-free synchronization, and fine-grained scheduling. In this piece we’ll only look at runtime code generation, which can be cleanly separated from the other […]

Verifying Popcount

Popcount is the function that returns the number of set bits in its argument. Showing that a popcount implementation does what it claims to do has become one of my favorite examples to use when I need to quickly show students how we can reason about programs mathematically. Something like a selection sort is probably […]

Walking or Biking to NSF

Since the National Science Foundation funds a large fraction of academic computer science research in the USA, we often end up traveling to Washington to visit the NSF. This post is just to say that if you are traveling light, if you need some exercise, if you have a bit of free time, and if the […]