Mehrdad Afshari

Ph.D. in Computer Science
Dissertation: Reimagining the Programming Experience

Publications

Liberating the Programmer with Prorogued Programming — SPLASH Onward! '12
Mehrdad Afshari, Earl Barr, Zhendong Su

Prorogued programming is a new programming paradigm closely aligned with the programmer's thought process by providing the ability to prorogue, to defer a concern, to focus on and finish the current concern, run and experiment with an incomplete program, and gradually and iteratively reify the missing parts while catching design and implementation mistakes early.

Compiler Validation via Equivalence Modulo Inputs — PLDI'14 Distinguished Paper
Vu Le, Mehrdad Afshari, Zhendong Su

[July 2016 — UPDATE]: Thus far, Orion, our initial realization of EMI, and its derivatives by my colleagues have collectively uncovered more than a thousand bugs in GCC and LLVM (Clang) projects, most of which have been confirmed and fixed by the developers of the respective compilers.

Equivalence modulo inputs (EMI) is a simple, widely applicable methodology for validating optimizing compilers. Our key insight is to exploit the close interplay between (1) dynamically executing a program on some test inputs and (2) statically compiling the program to work on all possible inputs. Indeed, the test inputs induce a natural collection of the original program's EMI variants, which can help differentially test any compiler and specifically target the difficult-to-find miscompilations. To create a practical implementation of EMI for validating C compilers, we profile a program's test executions and stochastically prune its unexecuted code. Our extensive testing in eleven months has led to 147 confirmed, unique bug reports for GCC and LLVM alone. The majority of those bugs are miscompilations, and more than 100 have already been fixed.

Toward Rapid Transformation of Ideas into Software — arXiv:1602.01075
Mehrdad Afshari, Zhendong Su

A key mission of computer science is to enable people realize their creative ideas as naturally and painlessly as possible. Software engineering is at the center of this mission — software technologies enable reification of ideas into working systems. As computers become ubiquitous, both in availability and the aspects of human lives they touch, the quantity and diversity of ideas also rapidly grow. Our programming systems and technologies need to evolve to make this reification process — transforming ideas to software — as quick and accessible as possible. The goal of this paper is twofold. First, it advocates and highlights the “transforming ideas to software” mission as a moonshot for software engineering research. This is a long-term direction for the community, and there is no silver bullet that can get us there. To make this mission a reality, as a community, we need to improve the status quo across many dimensions. Thus, the second goal is to outline a number of directions to modernize our contemporary programming technologies for decades to come, describe work that has been undertaken along those vectors, and pinpoint critical challenges.

Building White-Box Abstractions by Program Refinement — SPLASH Onward! '16
Mehrdad Afshari, Zhendong Su

Abstractions make building complex systems possible. Many facilities provided by a modern programming language are directly designed to build a certain style of abstraction. Abstractions also aim to enhance code reusability, thus enhancing programmer productivity and effectiveness. Real-world software systems can grow to have a complicated hierarchy of abstractions. Often, the hierarchy grows unnecessarily deep, because the programmers have envisioned the most generic use cases for a piece of code to make it reusable. Sometimes, the abstractions used in the program are not the appropriate ones, and it would be simpler for the higher level client to circumvent such abstractions. Another problem is the impedance mismatch between different pieces of code or libraries coming from different projects that are not designed to work together. Interoperability between such libraries are often hindered by abstractions, by design, in the name of hiding implementation details and encapsulation. These problems necessitate forms of abstraction that are easy to manipulate if needed. In this paper, we describe a powerful mechanism to create white-box abstractions, that encourage flatter hierarchies of abstraction and ease of manipulation and customization when necessary: program refinement. In so doing, we rely on the basic principle that writing directly in the host programming language is as least restrictive as one can get in terms of expressiveness, and allow the programmer to reuse and customize existing code snippets to address their specific needs.