Alive2 Part 3: Things You Can and Can’t Do with Undef in LLVM

[This piece is co-authored with Vsevolod Livinskii.] Formal verification isn’t some sort of magic pixie dust that we sprinkle over a computer system to make it better. Real formal verification involves a lot of the same kind of difficult, nasty, grungy engineering work that any other systems-level job involves. Furthermore, the verification tools...

Compilers can be improved over time, but this is a slow process. “Proebsting’s Law” is an old joke which suggested that advances in compiler optimization will double the speed of a computation every 18 years — but if anything this is optimistic. Slow compiler evolution is never a good thing, but this is particularly problematic […]

In its original form, a peephole optimization applied to a collection of instructions located close together in a program. For example, in a register transfer language we might find this sequence of instructions: r0 = xor r8, -1 r1 = xor r9, -1 r0 = and r0, r1 Here, assuming the two’s complement representation, -1 […]

[This piece is co-authored by Ryan Berger and Stefan Mada (both Utah CS undergrads), by Nader Boushehri, and by John Regehr.] An optimizing compiler traditionally has three main parts: a frontend that translates a source language into an intermediate representation (IR), a “middle end” that rewrites IR into better IR, and then a backend that […]

[This piece is coauthored by Yuyou Fan and John Regehr] Mutation-based fuzzing is based on the idea that new, bug-triggering inputs can often be created by randomly modifying existing, non-bug-triggering inputs. For example, if we wanted to find bugs in a PDF reader, we could grab a bunch of PDF files off the web, mutate […]