Latest Articles

## Higher-order Demand-driven Program Analysis

Developing accurate and efficient program analyses for languages with higher-order functions is known to be difficult. Here we define a new higher-order program analysis, Demand-Driven Program Analysis (DDPA), which extends well-known demand-driven lookup techniques found in first-order program analyses to higher-order programs. This task presents... (more)

## Failure Recovery in Resilient X10

Cloud computing has made the resources needed to execute large-scale in-memory distributed computations widely available. Specialized programming models, e.g., MapReduce, have emerged to offer transparent fault tolerance and fault recovery for specific computational patterns, but they sacrifice... (more)

## PYE: A Framework for Precise-Yet-Efficient Just-In-Time Analyses for Java Programs

Languages like Java and C# follow a two-step process of compilation: static compilation and just-in-time (JIT) compilation. As the time spent in JIT compilation gets added to the execution-time of the application, JIT compilers typically sacrifice the precision of program analyses for efficiency. The alternative of performing the analysis for... (more)

## Combinatorial Register Allocation and Instruction Scheduling

This article introduces a combinatorial optimization approach to register allocation and instruction scheduling, two central compiler problems.... (more)

## Static Identification of Injection Attacks in Java

The most dangerous security-related software errors, according to the OWASP Top Ten 2017 list, affect web applications. They are potential injection attacks that exploit user-provided data to execute undesired operations: database access and updates (SQL injection); generation of malicious web pages (cross-site scripting injection); redirection to user-specified web pages (redirect injection); execution of OS commands and arbitrary scripts (command injection); loading of user-specified, possibly... (more)

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##### Forthcoming Articles
Modular Product Programs

Many interesting program properties like determinism or information flow security are hyperproperties, that is, they relate multiple executions of the same program. Hyperproperties can be verified using relational logics, but these logics require dedicated tool support and are difficult to automate. Alternatively, constructions such as self-composition represent multiple executions of a program by one product program, thereby reducing hyperproperties of the original program to trace properties of the product. However, existing constructions do not fully support procedure specifications, for instance, to derive the determinism of a caller from the determinism of a callee, making verification non-modular. We present modular product programs, a novel kind of product program that permits hyperproperties in procedure specifications and, thus, can reason about calls modularly. We provide a general formalization of our product construction and prove it sound and complete. We demonstrate its expressiveness by applying it to information flow security with advanced features such as declassification and termination-sensitivity. Modular product programs can be verified using off-the-shelf verifiers; we have implemented our approach for both secure information flow and general hyperproperties using the Viper verification infrastructure. Our evaluation demonstrates that modular product programs can be used to prove hyperproperties for challenging examples in reasonable time.

Consistent Subtyping for All

Consistent subtyping is employed in some gradual type systems to validate type conversions. The original definition by Siek and Taha serves as a guideline for designing gradual type systems with subtyping. Polymorphic types à la System F also induce a subtyping relation that relates polymorphic types to their instantiations. However Siek and Tahas definition is not adequate for polymorphic subtyping. The first goal of this paper is to propose a generalization of consistent subtyping that is adequate for polymorphic subtyping, and subsumes the original definition by Siek and Taha. The new definition of consistent subtyping provides novel insights with respect to previous polymorphic gradual type systems, which did not employ consistent subtyping. The second goal of this paper is to present a gradually typed calculus for implicit (higher-rank) polymorphism that uses our new notion of consistent subtyping. We develop both declarative and (bidirectional) algorithmic versions for the type system. The algorithmic version employs techniques developed by Dunfield and Krishnaswami to deal with instantiation. We prove that the new calculus satisfies all static aspects of the refined criteria for gradual typing. We also study an extension of the type system with static and gradual type parameters, in an attempt to support a variant of the dynamic criterion for gradual typing. Armed with a coherence conjecture for the extended calculus, we show that the dynamic gradual guarantee of our source language can be reduced to that of »B, which, at the time of writing, is still an open question.

On the Impact of Programming Languages on Code Quality

This paper is a reproduction of work by Ray et al. which claimed to have uncovered a statistically significant association between eleven programming languages and software defects in projects hosted on GitHub. First we conduct an experimental repetition, repetition is only partially successful, but it does validate one of the key claims of the original work about the association of ten programming languages with defects. Next, we conduct a complete, independent reanalysis of the data and statistical modeling steps of the original study. We uncover a number of flaws that undermine the conclusions of the original study as only four languages are found to have a statistically significant association with defects, and even for those the effect size is exceedingly small. We conclude with some additional sources of bias that should be investigated in follow up 9 work and a few best practice recommendations for similar efforts.

Non-polynomial Worst-Case Analysis of Recursive Programs

We study the problem of developing efficient approaches for proving worst-case bounds of non-deterministic recursive programs. Ranking functions are sound and complete for proving termination and worst-case bounds of non-recursive programs. First, we apply ranking functions to recursion, resulting in measure functions. We show that measure functions provide a sound and complete approach to prove worst-case bounds of non-deterministic recursive programs. Our second contribution is the synthesis of measure functions in non-polynomial forms. We show that non-polynomial measure functions with logarithm and exponentiation can be synthesized through abstraction of logarithmic or exponentiation terms, Farkas' Lemma, and Handelman's Theorem using linear programming. While previous methods obtain polynomial worst-case bounds, our approach can synthesize bounds of various forms including $\mathcal{O}(n \log n)$ and $\mathcal{O}(n^r)$ where $r$ is not an integer. We present experimental results to demonstrate that our approach can efficiently obtain worst-case bounds of classical recursive algorithms such as (i)~Merge sort, Heap sort and the divide-and-conquer algorithm for the Closest Pair problem, where we obtain $\mathcal{O}(n \log n)$ worst-case bound, and (ii)~Karatsuba's algorithm for polynomial multiplication and Strassen's algorithm for matrix multiplication, for which we obtain $\mathcal{O}(n^r)$ bounds such that $r$ is not an integer and is close to the best-known bound for the respective algorithm. Besides the ability to synthesize non-polynomial bounds, we also show that our approach is equally capable of obtaining polynomial worst-case bounds for classical programs such as Quick sort and the dynamic programming algorithm for computing Fibonacci numbers.

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