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Dataflow Analyses and Compiler Optimizations that Use Them, for Free
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 computat...
Why Do Peephole Optimizations Work?
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...
Formal-Methods-Based Bugfinding for LLVM’s AArch64 Backend
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 ...
High-Throughput, Formal-Methods-Assisted Fuzzing for LLVM
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...
A Close Look at a Spinlock
The spinlock is the most basic mutual exclusion primitive provided by a multiprocessor operating system. Spinlocks need to protect against preemption on the current CPU (typically by disabling in...
llvm-reduce
Test-case reduction is more or less a necessity when debugging failures of complex programs such as compilers. Automated test-case reduction is useful not only because it allows developers to avo...
Responsible and Effective Bugfinding
NB: This piece is not about responsible disclosure of security issues. For almost as long as people have written code, we have also worked to create methods for finding software defects. Much mor...
Alive2 Part 3: Things You Can and Can’t Do with Undef in LLVM
Let’s talk about these functions: unsigned add(unsigned x) { return x + x; } unsigned shift(unsigned x) { return x << 1; } From the point of view of the C and C++ abstract machines, their beha...
The Gods Pocket Peak Trail
Years ago my friend Derek heard that the Jarbidge Wilderness — a remote, mountainous area along the Idaho-Nevada border — is one of the least-visited wilderness areas in the USA, and we’ve ...
You Might as Well Be a Great Copy Editor
An early draft of a paper, blog post, grant proposal, or other piece of technical writing typically has many problems. Some of these are high-level issues, such as weak motivation, sections in th...