title: Reliable and efficient programming abstractions for wireless sensor networks

authors:
Nupur Kothari
Ramakrishna Gummadi
Todd D. Millstein
Ramesh Govindan

abstract: It is currently difficult to build practical and reliable programming systems out of distributed and resource-constrained sensor devices. The state of the art in today's sensornet programming is centered around a component-based language called nesC. nesC is a node-level language-a program is written for an individual node in the network-and nesC programs use the services of an operating system called TinyOS. We are pursuing an approach to programming sensor networks that significantly raises the level of abstraction over this practice. The critical change is one of perspective: rather than writing programs from the point of view of an individual node, programmers implement a central program that conceptually has access to the entire network. This approach pushes to the compiler the task of producing node-level programs that implement the desired behavio.


venue: pldi

title: Effective automatic parallelization of stencil computations

authors:
Sriram Krishnamoorthy
Muthu Manikandan Baskaran
Uday Bondhugula
J. Ramanujam
Atanas Rountev
P. Sadayappan

abstract: Performance optimization of stencil computations has been widely studied in the literature, since they occur in many computationally intensive scientific and engineering applications. Compiler frameworks have also been developed that can transform sequential stencil codes for optimization of data locality and parallelism. However, loop skewing is typically required in order to tile stencil codes along the time dimension, resulting in load imbalance in pipelined parallel execution of the tiles. In this paper, we develop an approach for automatic parallelization of stencil codes, that explicitly addresses the issue of load-balanced execution of tiles. Experimental results are provided that demonstrate the effectiveness of the approach.


title: Optimistic parallelism requires abstractions

authors:
Milind Kulkarni
Keshav Pingali
Bruce Walter
Ganesh Ramanarayanan
Kavita Bala
L. Paul Chew

abstract: Irregular applications, which manipulate large, pointer-based data structures like graphs, are difficult to parallelize manually. Automatic tools and techniques such as restructuring compilers and run-time speculative execution have failed to uncover much parallelism in these applications, in spite of a lot of effort by the research community. These difficulties have even led some researchers to wonder if there is any coarse-grain parallelism worth exploiting in irregular applications.


title: Making context-sensitive points-to analysis with heap cloning practical for the real world

authors:
Chris Lattner
Andrew Lenharth
Vikram S. Adve

abstract: Context-sensitive pointer analysis algorithms with full "heapcloning" are powerful but are widely considered to be too expensive to include in production compilers. This paper shows, for the first time, that a context-sensitive, field-sensitive algorithm with fullheap cloning (by acyclic call paths) can indeed be both scalable and extremely fast in practice. Overall, the algorithm is able to analyze programs in the range of 100K-200K lines of C code in 1-3 seconds,takes less than 5% of the time it takes for GCC to compile the code (which includes no whole-program analysis), and scales well across five orders of magnitude of code size. It is also able to analyze the Linux kernel (about 355K linesof code) in 3.1 seconds. The paper describes the major algorithmic and engineering design choices that are required to achieve these results, including (a) using flow-insensitive and unification-basedanalysis, which are essential to avoid exponential behavior in practice;(b) sacrificing context-sensitivity within strongly connected components of the call graph; and (c) carefully eliminating several kinds of O(N2) behaviors (largely without affecting precision). The techniques used for (b) and (c) eliminated several major bottlenecks to scalability, and both are generalizable to other context-sensitive algorithms. We show that the engineering choices collectively reduce analysis time by factors of up to 10x-15xin our larger programs, and have found that the savings grow strongly with program size. Finally, we briefly summarize results demonstrating the precision of the analysis.


title: Searching for type-error messages

authors:
Benjamin S. Lerner
Matthew Flower
Dan Grossman
Craig Chambers

abstract: Advanced type systems often need some form of type inference to reduce the burden of explicit typing, but type inference often leads to poor error messages for ill-typed programs. This work pursues a new approach to constructing compilers and presenting type-error messages in which the type-checker itself does not produce the messages. Instead, it is an oracle for a search procedure that finds similar programs that do type-check. Our two-fold goal is to improve error messages while simplifying compiler construction. Our primary implementation and evaluation is for Caml, a language with full type inference. We also present a prototype for C++ template functions, where type instantiation is implicit. A key extension is making our approach robust even when the program has multiple independent type errors.


title: Profile-driven energy reduction in network-on-chips

authors:
Feihui Li
Guangyu Chen
Mahmut T. Kandemir
Ibrahim Kolcu

abstract: Reducing energy consumption of a Network-on-Chip (NoC) is a critical design goal, especially for power-constrained embedded systems.In response, prior research has proposed several circuit/architectural level mechanisms to reduce NoC power consumption. This paper considers the problem from a different perspective and demonstrates that compiler analysis can be very helpful for enhancing the effectiveness of a hardware-based link power management mechanism by increasing the duration of communication links' idle periods. The proposed profile-based approach achieves its goal by maximizing the communication link reuse through compiler-directed, static message re-routing. That is, it clusters the required data communications into a small set of communication links at any given time, which increases the idle periods for the remaining communication links in the network. This helps hardware shut down more communication links and their corresponding buffers to reduce leakage power. The current experimental evaluation, with twelve data-intensive embedded applications, shows that the proposed profile-driven compiler approach reduces leakage energy by more than 35% (on average) as compared to a pure hardware-based link power management scheme.


title: Combining events and threads for scalable network services implementation and evaluation of monadic, application-level concurrency primitives

authors:
Peng Li
Steve Zdancewic

abstract: This paper proposes to combine two seemingly opposed programming models for building massively concurrent network services: the event-driven model and the multithreaded model. The result is a hybrid design that offers the best of both worlds--the ease of use and expressiveness of threads and the flexibility and performance of events.


title: UCC: update-conscious compilation for energy efficiency in wireless sensor networks

authors:
Weijia Li
Youtao Zhang
Jun Yang
Jiang Zheng

abstract: Wireless sensor networks (WSN), composed of a large number of low-cost, battery-powered sensors, have recently emerged as promising computing platforms for many non-traditional applications. The preloaded code on remote sensors often needs to be updated after deployment in order for the WSN to adapt to the changing demands from the users. Post-deployment code dissemination is challenging as the data are transmitted via battery-powered wireless communication. Recent studies show that the energy for sending a single bit is about the same as executing 1000 instructions in aWSN. Therefore it is important to achieve energy efficiency in code dissemination.


title: A general framework for certifying garbage collectors and their mutators

authors:
Andrew McCreight
Zhong Shao
Chunxiao Lin
Long Li

abstract: Garbage-collected languages such as Java and C# are becoming more and more widely used in both high-end software and real-time embedded applications. The correctness of the GC implementation is essential to the reliability and security of a large portion of the world's mission-critical software. Unfortunately, garbage collectors--especially incremental and concurrent ones--are extremely hard to implement correctly. In this paper, we present a new uniform approach to verifying the safety of both a mutator and its garbage collector in Hoare-style logic. We define a formal garbage collector interface general enough to reason about a variety of algorithms while allowing the mutator to ignore implementation-specific details of the collector. Our approach supports collectors that require read and write barriers. We have used our approach to mechanically verify assembly implementations of mark-sweep, copying and incremental copying GCs in Coq, as well as sample mutator programs that can be linked with any of the GCs to produce a fully-verified garbage-collected program. Our work provides a foundation for reasoning about complex mutator-collector interaction and makes an important advance toward building fully certified production-quality GCs.


title: Automatic inversion generates divide-and-conquer parallel programs

authors:
Kazutaka Morita
Akimasa Morihata
Kiminori Matsuzaki
Zhenjiang Hu
Masato Takeichi

abstract: Divide-and-conquer algorithms are suitable for modern parallel machines, tending to have large amounts of inherent parallelism and working well with caches and deep memory hierarchies. Among others, list homomorphisms are a class of recursive functions on lists, which match very well with the divide-and-conquer paradigm. However, direct programming with list homomorphisms is a challenge for many programmers. In this paper, we propose and implement a novel systemthat can automatically derive cost-optimal list homomorphisms from a pair of sequential programs, based on the third homomorphism theorem. Our idea is to reduce extraction of list homomorphisms to derivation of weak right inverses. We show that a weak right inverse always exists and can be automatically generated from a wide class of sequential programs. We demonstrate our system with several nontrivial examples, including the maximum prefix sum problem, the prefix sum computation, the maximum segment sum problem, and the line-of-sight problem. The experimental results show practical efficiency of our automatic parallelization algorithm and good speedups of the generated parallel programs.


title: Iterative context bounding for systematic testing of multithreaded programs

authors:
Madanlal Musuvathi
Shaz Qadeer

abstract: Multithreaded programs are difficult to get right because of unexpected interaction between concurrently executing threads. Traditional testing methods are inadequate for catching subtle concurrency errors which manifest themselves late in the development cycle and post-deployment. Model checking or systematic exploration of program behavior is a promising alternative to traditional testing methods. However, it is difficult to perform systematic search on large programs as the number of possible program behaviors grows exponentially with the program size. Confronted with this state-explosion problem, traditional model checkers perform iterative depth-bounded search. Although effective for message-passing software, iterative depth-bounding is inadequate for multithreaded software.


title: Automatically classifying benign and harmful data racesallusing replay analysis

authors:
Satish Narayanasamy
Zhenghao Wang
Jordan Tigani
Andrew Edwards
Brad Calder

abstract: Many concurrency bugs in multi-threaded programs are due to dataraces. There have been many efforts to develop static and dynamic mechanisms to automatically find the data races. Most of the prior work has focused on finding the data races and eliminating the false positives.


title: Valgrind: a framework for heavyweight dynamic binary instrumentation

authors:
Nicholas Nethercote
Julian Seward

abstract: Dynamic binary instrumentation (DBI) frameworks make it easy to build dynamic binary analysis (DBA) tools such as checkers and profilers. Much of the focus on DBI frameworks has been on performance; little attention has been paid to their capabilities. As a result, we believe the potential of DBI has not been fully exploited.

awards: Most Influential PLDI Paper (awarded 2017)


title: Exterminator: automatically correcting memory errors with high probability

authors:
Gene Novark
Emery D. Berger
Benjamin G. Zorn

abstract: Programs written in C and C++ are susceptible to memory errors, including buffer overflows and dangling pointers. These errors, whichcan lead to crashes, erroneous execution, and security vulnerabilities, are notoriously costly to repair. Tracking down their location in the source code is difficult, even when the full memory state of the program is available. Once the errors are finally found, fixing them remains challenging: even for critical security-sensitive bugs, the average time between initial reports and the issuance of a patch is nearly one month.


title: Fault-tolerant typed assembly language

authors:
Frances Perry
Lester W. Mackey
George A. Reis
Jay Ligatti
David I. August
David Walker

abstract: A transient hardware fault occurs when an energetic particle strikes a transistor, causing it to change state. Although transient faults do not permanently damage the hardware, they may corrupt computations by altering stored values and signal transfers. In this paper, we propose a new scheme for provably safe and reliable computing in the presence of transient hardware faults. In our scheme, software computations are replicated to provide redundancy while special instructions compare the independently computed results to detect errors before writing critical data. In stark contrast to any previous efforts in this area, we have analyzed our fault tolerance scheme from a formal, theoretical perspective. To be specific, first, we provide an operational semantics for our assembly language, which includes a precise formal definition of our fault model. Second, we develop an assembly-level type system designed to detect reliability problems in compiled code. Third, we provide a formal specification for program fault tolerance under the given fault model and prove that all well-typed programs are indeed fault tolerant. In addition to the formal analysis, we evaluate our detection scheme and show that it only takes 34% longer to execute than the unreliable version.


title: Static specification inference using predicate mining

authors:
Murali Krishna Ramanathan
Ananth Grama
Suresh Jagannathan

abstract: The reliability and correctness of complex software systems can be significantly enhanced through well-defined specifications that dictate the use of various units of abstraction (e.g., modules, or procedures). Often times, however, specifications are either missing, imprecise, or simply too complex to encode within a signature, necessitating specification inference. The process of inferring specifications from complex software systems forms the focus of this paper. We describe a static inference mechanism for identifying the preconditions that must hold whenever a procedure is called. These preconditions may reflect both data flow properties (e.g., whenever p is called, variable x must be non-null) as well as control-flow properties (e.g., every call to p must bepreceded by a call to q). We derive these preconditions using a ninter-procedural path-sensitive dataflow analysis that gathers predicates at each program point. We apply mining techniques to these predicates to make specification inference robust to errors. This technique also allows us to derive higher-level specifications that abstract structural similarities among predicates (e.g., procedure p is called immediately after a conditional test that checks whether some variable v is non-null.) We describe an implementation of these techniques, and validate the effectiveness of the approach on a number of large open-source benchmarks. Experimental results confirm that our mining algorithms are efficient, and that the specifications derived are both precise and useful-the implementation discovers several critical, yet previously, undocumented preconditions for well-tested libraries.


title: Parameterized tiled loops for free

authors:
Lakshminarayanan Renganarayanan
DaeGon Kim
Sanjay V. Rajopadhye
Michelle Mills Strout

abstract: Parameterized tiled loops-where the tile sizes are not fixed at compile time, but remain symbolic parameters until later--are quite useful for iterative compilers and "auto-tuners" that produce highly optimized libraries and codes. Tile size parameterization could also enable optimizations such as register tiling to become dynamic optimizations. Although it is easy to generate such loops for (hyper) rectangular iteration spaces tiled with (hyper) rectangular tiles, many important computations do not fall into this restricted domain. Parameterized tile code generation for the general case of convex iteration spaces being tiled by (hyper) rectangular tiles has in the past been solved with bounding box approaches or symbolic Fourier Motzkin approaches. However, both approaches have less than ideal code generation efficiency and resulting code quality. We present the theoretical foundations, implementation, and experimental validation of a simple, unified technique for generating parameterized tiled code. Our code generation efficiency is comparable to all existing code generation techniques including those for fixed tile sizes, and the resulting code is as efficient as, if not more than, all previous techniques. Thus the technique provides parameterized tiled loops for free! Our "one-size-fits-all" solution, which is available as open source software can be adapted for use in production compilers.


title: Automatic inference of optimizer flow functions from semantic meanings

authors:
Erika Rice Scherpelz
Sorin Lerner
Craig Chambers

abstract: Previous work presented a language called Rhodium for writing program analyses and transformations, in the form of declarative flow functions that propagate instances of user-defined dataflow fact schemas. Each dataflow fact schema specifies a semantic meaning, which allows the Rhodium system to automatically verify the correctness of the user's flow functions. In this work, we have reversed the roles of the flow functions and semantic meanings: rather than checking the correctness of the user-written flow functions using the facts' semantic meanings, we automatically infer correct flow functions solely from the meanings of the dataflow fact schemas. We have implemented our algorithm for inferring flow functions from fact schemas in the context of the Whirlwind compiler, and have used this implementation to infer flow functions for a variety of fact schemas. The automatically generated flow functions cover most of the situations covered by an earlier suite of handwritten rules.


title: Online optimizations driven by hardware performance monitoring

authors:
Florian T. Schneider
Mathias Payer
Thomas R. Gross

abstract: Hardware performance monitors provide detailed direct feedback about application behavior and are an additional source of infor-mation that a compiler may use for optimization. A JIT compiler is in a good position to make use of such information because it is running on the same platform as the user applications. As hardware platforms become more and more complex, it becomes more and more difficult to model their behavior. Profile information that captures general program properties (like execution frequency of methods or basic blocks) may be useful, but does not capture sufficient information about the execution platform. Machine-level performance data obtained from a hardware performance monitor can not only direct the compiler to those parts of the program that deserve its attention but also determine if an optimization step actually improved the performance of the application.


title: DITTO: automatic incrementalization of data structure invariant checks (in Java)

authors:
Ajeet Shankar
Rastislav Bodík

abstract: We present DITTO, an automatic incrementalizer for dynamic, side-effect-free data structure invariant checks. Incrementalization speeds up the execution of a check by reusing its previous executions, checking the invariant anew only the changed parts of the data structure. DITTO exploits properties specific to the domain of invariant checks to automate and simplify the process without restricting what mutations the program can perform. Our incrementalizer works for modern imperative languages such as Java and C#. It can incrementalize,for example, verification of red-black tree properties and the consistency of the hash code in a hash table bucket. Our source-to-source implementation for Java is automatic, portable, and efficient. DITTO provides speedups on data structures with as few as 100 elements; on larger data structures, its speedups are characteristic of non-automatic incrementalizers: roughly 5-fold at 5,000 elements,and growing linearly with data structure size.


title: Enforcing isolation and ordering in STM

authors:
Tatiana Shpeisman
Vijay Menon
Ali-Reza Adl-Tabatabai
Steven Balensiefer
Dan Grossman
Richard L. Hudson
Katherine F. Moore
Bratin Saha

abstract: Transactional memory provides a new concurrency control mechanism that avoids many of the pitfalls of lock-based synchronization. High-performance software transactional memory (STM) implementations thus far provide weak atomicity: Accessing shared data both inside and outside a transaction can result in unexpected, implementation-dependent behavior. To guarantee isolation and consistent ordering in such a system, programmers are expected to enclose all shared-memory accesses inside transactions.


title: Sketching stencils

authors:
Armando Solar-Lezama
Gilad Arnold
Liviu Tancau
Rastislav Bodík
Vijay A. Saraswat
Sanjit A. Seshia

abstract: Performance of stencil computations can be significantly improved through smart implementations that improve memory locality, computation reuse, or parallelize the computation. Unfortunately, efficient implementations are hard to obtain because they often involve non-traditional transformations, which means that they cannot be produced by optimizing the reference stencil with a compiler. In fact, many stencils are produced by code generators that were tediously handcrafted.


title: Thin slicing

authors:
Manu Sridharan
Stephen J. Fink
Rastislav Bodík

abstract: Program slicing systematically identifies parts of a program relevant to a seed statement. Unfortunately, slices of modern programs often grow too large for human consumption. We argue that unwieldy slices arise primarily from an overly broad definition of relevance, rather than from analysis imprecision. While a traditional slice includes all statements that may affect a point of interest, not all such statements appear equally relevant to a human.


title: The ExoVM system for automatic VM and application reduction

authors:
Ben L. Titzer
Joshua S. Auerbach
David F. Bacon
Jens Palsberg

abstract: Embedded systems pose unique challenges to Java application developers and virtual machine designers. Chief among these challenges is the memory footprint of both the virtual machine and the applications that run within it. With the rapidly increasing set of features provided by the Java language, virtual machine designers are often forced to build custom implementations that make various tradeoffs between the footprint of the virtual machine and the subset of the Java language and class libraries that are supported. In this paper, we present the ExoVM, a system in which an application is initialized in a fully featured virtual machine, and then the code, data, and virtual machine features necessary to execute it are packaged into a binary image. Key to this process is feature analysis, a technique for computing the reachable code and data of a Java program and its implementation inside the VM simultaneously. The ExoVM reduces the need to develop customized embedded virtual machines by reusing a single VM infrastructure and automatically eliding the implementation of unused Java features on a per-program basis. We present a constraint-based instantiation of the analysis technique, an implementation in IBM's J9 Java VM, experiments evaluating our technique for the EEMBC benchmark suite, and some discussion of the individual costs of some of Java's features. Our evaluation shows that our system can reduce the non-heap memory allocation of the virtual machine by as much as 75%. We discuss VM and language design decisions that our work shows are important in targeting embedded systems, supporting the long-term goal of a common VM infrastructure spanning from motes to large servers.


title: CGCExplorer: a semi-automated search procedure for provably correct concurrent collectors

authors:
Martin T. Vechev
Eran Yahav
David F. Bacon
Noam Rinetzky

abstract: Concurrent garbage collectors are notoriously hard to design, implement, and verify. We present a framework for the automatic exploration of a space of concurrent mark-and-sweep collectors. In our framework, the designer specifies a set of "building blocks" from which algorithms can be constructed. These blocks reflect the designer's insights about the coordination between the collector and the mutator. Given a set of building blocks, our framework automatically explores a space of algorithms, using model checking with abstraction to verify algorithms in the space.


title: EXOCHI: architecture and programming environment for a heterogeneous multi-core multithreaded system

authors:
Perry H. Wang
Jamison D. Collins
Gautham N. Chinya
Hong Jiang
Xinmin Tian
Milind Girkar
Nick Y. Yang
Guei-Yuan Lueh
Hong Wang

abstract: Future mainstream microprocessors will likely integrate specialized accelerators, such as GPUs, onto a single die to achieve better performance and power efficiency. However, it remains a keen challenge to program such a heterogeneous multicore platform, since these specialized accelerators feature ISAs and functionality that are significantly different from the general purpose CPU cores. In this paper, we present EXOCHI: (1) Exoskeleton Sequencer(EXO), an architecture to represent heterogeneous acceleratorsas ISA-based MIMD architecture resources, and a shared virtual memory heterogeneous multithreaded program execution model that tightly couples specialized accelerator cores with generalpurpose CPU cores, and (2) C for Heterogeneous Integration(CHI), an integrated C/C++ programming environment that supports accelerator-specific inline assembly and domain-specific languages. The CHI compiler extends the OpenMP pragma for heterogeneous multithreading programming, and produces a single fat binary with code sections corresponding to different instruction sets. The runtime can judiciously spread parallel computation across the heterogeneous cores to optimize performance and power.


title: Sound and precise analysis of web applications for injection vulnerabilities

authors:
Gary Wassermann
Zhendong Su

abstract: Web applications are popular targets of security attacks. One common type of such attacks is SQL injection, where an attacker exploits faulty application code to execute maliciously crafted database queries. Bothstatic and dynamic approaches have been proposed to detect or prevent SQL injections; while dynamic approaches provide protection for deployed software, static approaches can detect potential vulnerabilities before software deployment. Previous static approaches are mostly based on tainted information flow tracking and have at least some of the following limitations: (1) they do not model the precise semantics of input sanitization routines; (2) they require manually written specifications, either for each query or for bug patterns; or (3) they are not fully automated and may require user intervention at various points in the analysis. In this paper, we address these limitations by proposing a precise, sound, and fully automated analysis technique for SQL injection. Our technique avoids the need for specifications by consideringas attacks those queries for which user input changes the intended syntactic structure of the generated query. It checks conformance to this policy byconservatively characterizing the values a string variable may assume with a context free grammar, tracking the nonterminals that represent user-modifiable data, and modeling string operations precisely as language transducers. We have implemented the proposed technique for PHP, the most widely-used web scripting language. Our tool successfully discovered previously unknown and sometimes subtle vulnerabilities in real-world programs, has a low false positive rate, and scales to large programs (with approx. 100K loc).


title: Towards locating execution omission errors

authors:
Xiangyu Zhang
Sriraman Tallam
Neelam Gupta
Rajiv Gupta

abstract: Execution omission errors are known to be difficult to locate using dynamic analysis. These errors lead to a failure at runtime because of the omission of execution of some statements that would have been executed if the program had no errors. Since dynamic analysis is typically designed to focus on dynamic information arising from executed statements, and statements whose execution is omitted do not produce dynamic information, detection of execution omission errors becomes a challenging task. For example, while dynamic slices are very effective in capturing faulty code for other types of errors, they fail to capture faulty code in presence of execution omission errors. To address this issue relevant slices have been defined to consider certain static dependences (called potential dependences) in addition to dynamic dependences. However, due to the conservative nature of static analysis, overly large slices are produced. In this paper, we propose a fully dynamic solution to locating execution omission errors using dynamic slices. We introduce the notion of implicit dependences which are dependences that are normally invisible to dynamic slicing due to the omission of execution of some statements. We design a dynamic method that forces the execution of the omitted code by switching outcomes of relevant predicates such that those implicit dependences are exposed and become available for dynamic slicing. Dynamic slices can be computed and effectively pruned to produce fault candidate sets containing the execution omission errors. We solve two main problems: verifying the existence of a single implicit dependence through predicate switching, and recovering the implicit dependences in a demand driven manner such that a small number of verifications are required before the root cause is captured. Our experiments show that the proposed technique is highly effective in capturing execution omission errors.


title: Automatic volume management for programmable microfluidics

authors:
Ahmed M. Amin
Mithuna Thottethodi
T. N. Vijaykumar
Steven Wereley
Stephen C. Jacobson

abstract: Microfluidics has enabled lab-on-a-chip technology to miniaturize and integrate biological and chemical analyses to a single chip comprising channels, valves, mixers, heaters, separators, and sensors. Recent papers have proposed programmable labs-on-a-chip as an alternative to traditional application-specific chips to reduce design effort, time, and cost. While these previous papers provide the basic support for programmability, this paper identifies and addresses a practical issue, namely, fluid volume management. Volume management addresses the problem that the use of a fluid depletes it and unless the given volume of a fluid is distributed carefully among all its uses, execution may run out of the fluid before all its uses are complete. Additionally, fluid volumes should not overflow (i.e., exceed hardware capacity) or underflow (i.e., fall below hardware resolution). We show that the problem can be formulated as a linear programming problem (LP). Because LP's complexity and slow execution times in practice may be a concern, we propose another approach, called DAGSolve, which over-constrains the problem to achieve linear complexity while maintaining good solution quality. We also propose two optimizations, called cascading and static replication, to handle cases involving extreme mix ratios and numerous fluid uses which may defeat both LP and DAGSolve. Using some real-world assays, we show that our techniques produce good solutions while being faster than LP.


title: SharC: checking data sharing strategies for multithreaded C

authors:
Zachary R. Anderson
David Gay
Robert Ennals
Eric A. Brewer

abstract: Unintended or unmediated data sharing is a frequent cause of insidious bugs in multithreaded programs. We present a tool called SharC (short for Sharing Checker) that allows a user to write lightweight annotations to declare how they believe objects are being shared between threads in their program. SharC uses a combination of static and dynamic analyses to check that the program conforms to this specification.


title: Immix: a mark-region garbage collector with space efficiency, fast collection, and mutator performance

authors:
Stephen M. Blackburn
Kathryn S. McKinley

abstract: Programmers are increasingly choosing managed languages for modern applications, which tend to allocate many short-to-medium lived small objects. The garbage collector therefore directly determines program performance by making a classic space-time tradeoff that seeks to provide space efficiency, fast reclamation, and mutator performance. The three canonical tracing garbage collectors: semi-space, mark-sweep, and mark-compact each sacrifice one objective. This paper describes a collector family, called mark-region , and introduces opportunistic defragmentation, which mixes copying and marking in a single pass. Combining both, we implement immix , a novel high performance garbage collector that achieves all three performance objectives. The key insight is to allocate and reclaim memory in contiguous regions, at a coarse block grain when possible and otherwise in groups of finer grain lines . We show that immix outperforms existing canonical algorithms, improving total application performance by 7 to 25% on average across 20 benchmarks. As the mature space in a generational collector, immix matches or beats a highly tuned generational collector, e.g. it improves jbb2000 by 5%. These innovations and the identification of a new family of collectors open new opportunities for garbage collector design.


title: Foundations of the C++ concurrency memory model

authors:
Hans-Juergen Boehm
Sarita V. Adve

abstract: Currently multi-threaded C or C++ programs combine a single-threaded programming language with a separate threads library. This is not entirely sound [7].


title: A practical automatic polyhedral parallelizer and locality optimizer

authors:
Uday Bondhugula
Albert Hartono
J. Ramanujam
P. Sadayappan

abstract: We present the design and implementation of an automatic polyhedral source-to-source transformation framework that can optimize regular programs (sequences of possibly imperfectly nested loops) for parallelism and locality simultaneously. Through this work, we show the practicality of analytical model-driven automatic transformation in the polyhedral model -- far beyond what is possible by current production compilers. Unlike previous works, our approach is an end-to-end fully automatic one driven by an integer linear optimization framework that takes an explicit view of finding good ways of tiling for parallelism and locality using affine transformations. The framework has been implemented into a tool to automatically generate OpenMP parallel code from C program sections. Experimental results from the tool show very high speedups for local and parallel execution on multi-cores over state-of-the-art compiler frameworks from the research community as well as the best native production compilers. The system also enables the easy use of powerful empirical/iterative optimization for general arbitrarily nested loop sequences.

awards: Most Influential PLDI Paper (awarded 2018)


title: Type-preserving compilation for large-scale optimizing object-oriented compilers

authors:
Juan Chen
Chris Hawblitzel
Frances Perry
Michael Emmi
Jeremy Condit
Derrick Coetzee
Polyvios Pratikakis

abstract: Type-preserving compilers translate well-typed source code, such as Java or C#, into verifiable target code, such as typed assembly language or proof-carrying code. This paper presents the implementation of type-preserving compilation in a complex, large-scale optimizing compiler. Compared to prior work, this implementation supports extensive optimizations, and it verifies a large portion of the interface between the compiler and the runtime system. This paper demonstrates the practicality of type-preserving compilation in complex optimizing compilers: the generated typed assembly language is only 2.3% slower than the base compiler's generated untyped assembly language, and the type-preserving compiler is 82.8% slower than the base compiler.


title: Inferring locks for atomic sections

authors:
Sigmund Cherem
Trishul M. Chilimbi
Sumit Gulwani

abstract: Atomic sections are a recent and popular idiom to support the development of concurrent programs. Updates performed within an atomic section should not be visible to other threads until the atomic section has been executed entirely. Traditionally, atomic sections are supported through the use of optimistic concurrency, either using a transactional memory hardware, or an equivalent software emulation (STM).


title: Dataflow analysis for concurrent programs using datarace detection

authors:
Ravi Chugh
Jan Wen Voung
Ranjit Jhala
Sorin Lerner

abstract: Dataflow analyses for concurrent programs differ from their single-threaded counterparts in that they must account for shared memory locations being overwritten by concurrent threads. Existing dataflow analysis techniques for concurrent programs typically fall at either end of a spectrum: at one end, the analysis conservatively kills facts about all data that might possibly be shared by multiple threads; at the other end, a precise thread-interleaving analysis determines which data may be shared, and thus which dataflow facts must be invalidated. The former approach can suffer from imprecision, whereas the latter does not scale.


title: Sound, complete and scalable path-sensitive analysis

authors:
Isil Dillig
Thomas Dillig
Alex Aiken

abstract: We present a new, precise technique for fully path- and context-sensitive program analysis. Our technique exploits two observations: First, using quantified, recursive formulas, path- and context-sensitive conditions for many program properties can be expressed exactly. To compute a closed form solution to such recursive constraints, we differentiate between observable and unobservable variables, the latter of which are existentially quantified in our approach. Using the insight that unobservable variables can be eliminated outside a certain scope, our technique computes satisfiability- and validity-preserving closed-form solutions to the original recursive constraints. We prove the solution is as precise as the original system for answering may and must queries as well as being small in practice, allowing our technique to scale to the entire Linux kernel, a program with over 6 million lines of code.


title: Explaining failures of program analyses

authors:
Daniel von Dincklage
Amer Diwan

abstract: With programs getting larger and often more complex with each new release, programmers need all the help they can get in understanding and transforming programs. Fortunately, modern development environments, such as Eclipse, incorporate tools for understanding, navigating, and transforming programs. These tools typically use program analyses to extract relevant properties of programs.


title: Certifying low-level programs with hardware interrupts and preemptive threads

authors:
Xinyu Feng
Zhong Shao
Yuan Dong
Yu Guo

abstract: Hardware interrupts are widely used in the world's critical software systems to support preemptive threads, device drivers, operating system kernels, and hypervisors. Handling interrupts properly is an essential component of low-level system programming. Unfortunately, interrupts are also extremely hard to reason about: they dramatically alter the program control flow and complicate the invariants in low-level concurrent code (e.g., implementation of synchronization primitives). Existing formal verification techniques---including Hoare logic, typed assembly language, concurrent separation logic, and the assume-guarantee method---have consistently ignored the issues of interrupts; this severely limits the applicability and power of today's program verification systems.


title: Velodrome: a sound and complete dynamic atomicity checker for multithreaded programs

authors:
Cormac Flanagan
Stephen N. Freund
Jaeheon Yi

abstract: Atomicity is a fundamental correctness property in multithreaded programs, both because atomic code blocks are amenable to sequential reasoning (which significantly simplifies correctness arguments), and because atomicity violations often reveal defects in a program's synchronization structure. Unfortunately, all atomicity analyses developed to date are incomplete in that they may yield false alarms on correctly synchronized programs, which limits their usefulness.


title: Grammar-based whitebox fuzzing

authors:
Patrice Godefroid
Adam Kiezun
Michael Y. Levin

abstract: Whitebox fuzzing is a form of automatic dynamic test generation, based on symbolic execution and constraint solving, designed for security testing of large applications. Unfortunately, the current effectiveness of whitebox fuzzing is limited when testing applications with highly-structured inputs, such as compilers and interpreters. These applications process their inputs in stages, such as lexing, parsing and evaluation. Due to the enormous number of control paths in early processing stages, whitebox fuzzing rarely reaches parts of the application beyond those first stages.


title: Model checking transactional memories

authors:
Rachid Guerraoui
Thomas A. Henzinger
Barbara Jobstmann
Vasu Singh

abstract: Model checking software transactional memories (STMs) is difficult because of the unbounded number, length, and delay of concurrent transactions and the unbounded size of the memory. We show that, under certain conditions, the verification problem can be reduced to a finite-state problem, and we illustrate the use of the method by proving the correctness of several STMs, including two-phase locking, DSTM, TL2, and optimistic concurrency control. The safety properties we consider include strict serializability and opacity; the liveness properties include obstruction freedom, livelock freedom, and wait freedom.


title: Program analysis as constraint solving

authors:
Sumit Gulwani
Saurabh Srivastava
Ramarathnam Venkatesan

abstract: A constraint-based approach to invariant generation in programs translates a program into constraints that are solved using off-the-shelf constraint solvers to yield desired program invariants.


title: Copy coalescing by graph recoloring

authors:
Sebastian Hack
Gerhard Goos

abstract: Register allocation is always a trade-off between live-range splitting and coalescing. Live-range splitting generally leads to less spilling at the cost of inserting shuffle code. Coalescing removes shuffle code while potentially raising the register demand and causing spilling.


title: Discovering properties about arrays in simple programs

authors:
Nicolas Halbwachs
Mathias Péron

abstract: Array bound checking and array dependency analysis (for parallelization) have been widely studied. However, there are much less results about analyzing properties of array contents. In this paper, we propose a way of using abstract interpretation for discovering properties about array contents in some restricted cases: one-dimensional arrays, traversed by simple "for" loops. The basic idea, borrowed from [GRS05], consists in partitioning arrays into symbolic intervals (e.g., [1,i -- 1], [i,i], [i + 1,n]), and in associating with each such interval I and each array A an abstract variable AI; the new idea is to consider relational abstract properties ψ(AI, BI, ...) about these abstract variables, and to interpret such a property pointwise on the interval I: ∀l ∈ I, ψ(A[l], B[l],...). The abstract semantics of our simple programs according to these abstract properties has been defined and implemented in a prototype tool. The method is able, for instance, to discover that the result of an insertion sort is a sorted array, or that, in an array traversal guarded by a "sentinel", the index stays within the bounds.


title: Expressive and safe static reflection with MorphJ

authors:
Shan Shan Huang
Yannis Smaragdakis

abstract: Recently, language extensions have been proposed for Java and C# to support pattern-based reflective declaration. These extensions introduce a disciplined form of meta-programming and aspect-oriented programming to mainstream languages: They allow members of a class (i.e., fields and methods) to be declared by statically iterating over and pattern-matching on members of other classes. Such techniques, however, have been unable to safely express simple, but common, idioms such as declaring getter and setter methods for fields.


title: Bootstrapping: a technique for scalable flow and context-sensitive pointer alias analysis

abstract: We propose a framework for improving both the scalability as well as the accuracy of pointer alias analysis, irrespective of its flow or context-sensitivities, by leveraging a three-pronged strategy that effectively combines divide and conquer, parallelization and function summarization. A key step in our approach is to first identify small subsets of pointers such that the problem of computing aliases of any pointer can be reduced to computing them in these small subsets instead of the entire program. In order to identify these subsets, we first apply a series of increasingly accurate but highly scalable (context and flow-insensitive) alias analyses in a cascaded fashion such that each analysis Ai works on the subsets generated by the previous one Ai-1. Restricting the application of Ai to subsets generated by Ai-1, instead of the entire program, improves it scalability, i.e., Ai is bootstrapped by Ai-1. Once these small subsets have been computed, in order to make our overall analysis accurate, we employ our new summarization-based flow and context-sensitive alias analysis. The small size of each subset offsets the higher computational complexity of the context-sensitive analysis. An important feature of our framework is that the analysis for each of the subsets can be carried out independently of others thereby allowing us to leverage parallelization further improving scalability.


title: Orchestrating the execution of stream programs on multicore platforms

authors:
Manjunath Kudlur
Scott A. Mahlke

abstract: While multicore hardware has become ubiquitous, explicitly parallel programming models and compiler techniques for exploiting parallelism on these systems have noticeably lagged behind. Stream programming is one model that has wide applicability in the multimedia, graphics, and signal processing domains. Streaming models execute as a set of independent actors that explicitly communicate data through channels. This paper presents a compiler technique for planning and orchestrating the execution of streaming applications on multicore platforms. An integrated unfolding and partitioning step based on integer linear programming is presented that unfolds data parallel actors as needed and maximally packs actors onto cores. Next, the actors are assigned to pipeline stages in such a way that all communication is maximally overlapped with computation on the cores. To facilitate experimentation, a generalized code generation template for mapping the software pipeline onto the Cell architecture is presented. For a range of streaming applications, a geometric mean speedup of 14.7x is achieved on a 16-core Cell platform compared to a single core.


title: Quantitative information flow as network flow capacity

authors:
Stephen McCamant
Michael D. Ernst

abstract: Abstract We present a new technique for determining how much informationabout a program's secret inputs is revealed by its public outputs. In


title: Fair stateless model checking

authors:
Madanlal Musuvathi
Shaz Qadeer

abstract: Stateless model checking is a useful state-space exploration technique for systematically testing complex real-world software. Existing stateless model checkers are limited to the verification of safety properties on terminating programs. However, realistic concurrent programs are nonterminating, a property that significantly reduces the efficacy of stateless model checking in testing them. Moreover, existing stateless model checkers are unable to verify that a nonterminating program satisfies the important liveness property of livelock-freedom, a property that requires the program to make continuous progress for any input.


title: Register allocation by puzzle solving

authors:
Fernando Magno Quintão Pereira
Jens Palsberg

abstract: We show that register allocation can be viewed as solving a collection of puzzles. We model the register file as a puzzle board and the program variables as puzzle pieces; pre-coloring and register aliasing fit in naturally. For architectures such as PowerPC, x86, and StrongARM, we can solve the puzzles in polynomial time, and we have augmented the puzzle solver with a simple heuristic for spilling. For SPEC CPU2000, the compilation time of our implementation is as fast as that of the extended version of linear scan used by LLVM, which is the JIT compiler in the openGL stack of Mac OS 10.5. Our implementation produces x86 code that is of similar quality to the code produced by the slower, state-of-the-art iterated register coalescing of George and Appel with the extensions proposed by Smith, Ramsey, and Holloway in 2004.


title: A study of concurrent real-time garbage collectors

authors:
Filip Pizlo
Erez Petrank
Bjarne Steensgaard

abstract: Concurrent garbage collection is highly attractive for real-time systems, because offloading the collection effort from the executing threads allows faster response, allowing for extremely short deadlines at the microseconds level. Concurrent collectors also offer much better scalability over incremental collectors. The main problem with concurrent real-time collectors is their complexity. The first concurrent real-time garbage collector that can support fine synchronization, STOPLESS, has recently been presented by Pizlo et al. In this paper, we propose two additional (and different) algorithms for concurrent real-time garbage collection: CLOVER and CHICKEN. Both collectors obtain reduced complexity over the first collector STOPLESS, but need to trade a benefit for it. We study the algorithmic strengths and weaknesses of CLOVER and CHICKEN and compare them to STOPLESS. Finally, we have implemented all three collectors on the Bartok compiler and runtime for C# and we present measurements to compare their efficiency and responsiveness.


title: Iterative optimization in the polyhedral model: part ii, multidimensional time

authors:
Louis-Noël Pouchet
Cédric Bastoul
Albert Cohen
John Cavazos

abstract: High-level loop optimizations are necessary to achieve good performance over a wide variety of processors. Their performance impact can be significant because they involve in-depth program transformations that aim to sustain a balanced workload over the computational, storage, and communication resources of the target architecture. Therefore, it is mandatory that the compiler accurately models the target architecture as well as the effects of complex code restructuring.


title: Liquid types

authors:
Patrick Maxim Rondon
Ming Kawaguchi
Ranjit Jhala

abstract: We present Logically Qualified Data Types, abbreviated to Liquid Types, a system that combines Hindley-Milner type inference with Predicate Abstraction to automatically infer dependent types precise enough to prove a variety of safety properties. Liquid types allow programmers to reap many of the benefits of dependent types, namely static verification of critical properties and the elimination of expensive run-time checks, without the heavy price of manual annotation. We have implemented liquid type inference in DSOLVE, which takes as input an OCAML program and a set of logical qualifiers and infers dependent types for the expressions in the OCAML program. To demonstrate the utility of our approach, we describe experiments using DSOLVE to statically verify the safety of array accesses on a set of OCAML benchmarks that were previously annotated with dependent types as part of the DML project. We show that when used in conjunction with a fixed set of array bounds checking qualifiers, DSOLVE reduces the amount of manual annotation required for proving safety from 31% of program text to under 1%.


title: Race directed random testing of concurrent programs

abstract: Bugs in multi-threaded programs often arise due to data races. Numerous static and dynamic program analysis techniques have been proposed to detect data races. We propose a novel randomized dynamic analysis technique that utilizes potential data race information obtained from an existing analysis tool to separate real races from false races without any need for manual inspection. Specifically, we use potential data race information obtained from an existing dynamic analysis technique to control a random scheduler of threads so that real race conditions get created with very high probability and those races get resolved randomly at runtime. Our approach has several advantages over existing dynamic analysis tools. First, we can create a real race condition and resolve the race randomly to see if an error can occur due to the race. Second, we can replay a race revealing execution efficiently by simply using the same seed for random number generation--we do not need to record the execution. Third, our approach has very low overhead compared to other precise dynamic race detection techniques because we only track all synchronization operations and a single pair of memory access statements that are reported to be in a potential race by an existing analysis. We have implemented the technique in a prototype tool for Java and have experimented on a number of large multi-threaded Java programs. We report a number of previously known and unknown bugs and real races in these Java programs.


title: Sketching concurrent data structures

authors:
Armando Solar-Lezama
Christopher Grant Jones
Rastislav Bodík

abstract: We describe PSketch, a program synthesizer that helps programmers implement concurrent data structures. The system is based on the concept of sketching, a form of synthesis that allows programmers to express their insight about an implementation as a partial program: a sketch. The synthesizer automatically completes the sketch to produce an implementation that matches a given correctness criteria.


title: Checking race freedom via linear programming

abstract: We present a new static analysis for race freedom and race detection. The analysis checks race freedom by reducing the problem to (rational) linear programming. Unlike conventional static analyses for race freedom or race detection, our analysis avoids explicit computation of locksets and lock linearity/must-aliasness. Our analysis can handle a variety of synchronization idioms that more conventional approaches often have difficulties with, such as thread joining, semaphores, and signals. We achieve efficiency by utilizing modern linear programming solvers that can quickly solve large linear programming instances. This paper reports on the formal properties of the analysis and the experience with applying an implementation to real world C programs.


title: Deriving linearizable fine-grained concurrent objects

authors:
Martin T. Vechev
Eran Yahav

abstract: Practical and efficient algorithms for concurrent data structures are difficult to construct and modify. Algorithms in the literature are often optimized for a specific setting, making it hard to separate the algorithmic insights from implementation details. The goal of this work is to systematically construct algorithms for a concurrent data structure starting from its sequential implementation. Towards that goal, we follow a construction process that combines manual steps corresponding to high-level insights with automatic exploration of implementation details. To assist us in this process, we built a new tool called Paraglider. The tool quickly explores large spaces of algorithms and uses bounded model checking to check linearizability of algorithms.


title: Conditional correlation analysis for safe region-based memory management

authors:
Xi Wang
Zhilei Xu
Xuezheng Liu
Zhenyu Guo
Xiaoge Wang
Zheng Zhang

abstract: Region-based memory management is a popular scheme in systems software for better organization and performance. In the scheme, a developer constructs a hierarchy of regions of different lifetimes and allocates objects in regions. When the developer deletes a region, the runtime will recursively delete all its subregions and simultaneously reclaim objects in the regions. The developer must construct a consistent placement of objects in regions; otherwise, if a region that contains pointers to other regions is not always deleted before pointees, an inconsistency will surface and cause dangling pointers, which may lead to either crashes or leaks.


title: XMem: type-safe, transparent, shared memory for cross-runtime communication and coordination

authors:
Michal Wegiel
Chandra Krintz

abstract: Developers commonly build contemporary enterprise applications using type-safe, component-based platforms, such as J2EE, and architect them to comprise multiple tiers, such as a web container, application server, and database engine. Administrators increasingly execute each tier in its own managed runtime environment (MRE) to improve reliability and to manage system complexity through the fault containment and modularity offered by isolated MRE instances. Such isolation, however, necessitates expensive cross-tier communication based on protocols such as object serialization and remote procedure calls. Administrators commonly co-locate communicating MREs on a single host to reduce communication overhead and to better exploit increasing numbers of available processing cores. However, state-of-the-art MREs offer no support for more efficient communication between co-located MREs, while fast inter-process communication mechanisms, such as shared memory, are widely available as a standard operating system service on most modern platforms.


title: Efficient program execution indexing

authors:
Bin Xin
William N. Sumner
Xiangyu Zhang

abstract: Execution indexing uniquely identifies a point in an execution. Desirable execution indices reveal correlations between points in an execution and establish correspondence between points across multiple executions. Therefore, execution indexing is essential for a wide variety of dynamic program analyses, for example, it can be used to organize program profiles; it can precisely identify the point in a re-execution that corresponds to a given point in an original execution and thus facilitate debugging or dynamic instrumentation. In this paper, we formally define the concept of execution index and propose an indexing scheme based on execution structure and program state. We present a highly optimized online implementation of the technique. We also perform a client study, which targets producing a failure inducing schedule for a data race by verifying the two alternative happens-before orderings of a racing pair. Indexing is used to precisely locate corresponding points across multiple executions in the presence of non-determinism so that no heavyweight tracing/replay system is needed.


title: Full functional verification of linked data structures

authors:
Karen Zee
Viktor Kuncak
Martin C. Rinard

abstract: We present the first verification of full functional correctness for a range of linked data structure implementations, including mutable lists, trees, graphs, and hash tables. Specifically, we present the use of the Jahob verification system to verify formal specifications, written in classical higher-order logic, that completely capture the desired behavior of the Java data structure implementations (with the exception of properties involving execution time and/or memory consumption). Given that the desired correctness properties include intractable constructs such as quantifiers, transitive closure, and lambda abstraction, it is a challenge to successfully prove the generated verification conditions.


title: GC assertions: using the garbage collector to check heap properties

authors:
Edward Aftandilian
Samuel Z. Guyer

abstract: This paper introduces GC assertions, a system interface that programmers can use to check for errors, such as data structure invariant violations, and to diagnose performance problems, such as memory leaks. GC assertions are checked by the garbage collector, which is in a unique position to gather information and answer questions about the lifetime and connectivity of objects in the heap. By piggybacking on existing garbage collector computations, our system is able to check heap properties with very low overhead -- around 3% of total execution time -- low enough for use in a deployed setting.


title: Lightweight annotations for controlling sharing in concurrent data structures

authors:
Zachary R. Anderson
David Gay
Mayur Naik

abstract: SharC is a recently developed system for checking data-sharing in multithreaded programs. Programmers specify sharing rules (read-only, protected by a lock, etc.) for individual objects, and the SharC compiler enforces these rules using static and dynamic checks. Violations of these rules indicate unintended data sharing, which is the underlying cause of harmful data-races. Additionally, SharC allows programmers to change the sharing rules for a specific object using a sharing cast, to capture the fact that sharing rules for an object often change during the object's lifetime. SharC was successfully applied to a number of multi-threaded C programs.


title: PetaBricks: a language and compiler for algorithmic choice

authors:
Jason Ansel
Cy P. Chan
Yee Lok Wong
Marek Olszewski
Qin Zhao
Alan Edelman
Saman P. Amarasinghe

abstract: It is often impossible to obtain a one-size-fits-all solution for high performance algorithms when considering different choices for data distributions, parallelism, transformations, and blocking. The best solution to these choices is often tightly coupled to different architectures, problem sizes, data, and available system resources. In some cases, completely different algorithms may provide the best performance. Current compiler and programming language techniques are able to change some of these parameters, but today there is no simple way for the programmer to express or the compiler to choose different algorithms to handle different parts of the data. Existing solutions normally can handle only coarse-grained, library level selections or hand coded cutoffs between base cases and recursive cases.


title: Snugglebug: a powerful approach to weakest preconditions

authors:
Satish Chandra
Stephen J. Fink
Manu Sridharan

abstract: Symbolic analysis shows promise as a foundation for bug-finding, specification inference, verification, and test generation. This paper addresses demand-driven symbolic analysis for object-oriented programs and frameworks. Many such codes comprise large, partial programs with highly dynamic behaviors--polymorphism, reflection, and so on--posing significant scalability challenges for any static analysis.


title: Staged information flow for javascript

authors:
Ravi Chugh
Jeffrey A. Meister
Ranjit Jhala
Sorin Lerner

abstract: Modern websites are powered by JavaScript, a flexible dynamic scripting language that executes in client browsers. A common paradigm in such websites is to include third-party JavaScript code in the form of libraries or advertisements. If this code were malicious, it could read sensitive information from the page or write to the location bar, thus redirecting the user to a malicious page, from which the entire machine could be compromised. We present an information-flow based approach for inferring the effects that a piece of JavaScript has on the website in order to ensure that key security properties are not violated. To handle dynamically loaded and generated JavaScript, we propose a framework for staging information flow properties. Our framework propagates information flow through the currently known code in order to compute a minimal set of syntactic residual checks that are performed on the remaining code when it is dynamically loaded. We have implemented a prototype framework for staging information flow. We describe our techniques for handling some difficult features of JavaScript and evaluate our system's performance on a variety of large real-world websites. Our experiments show that static information flow is feasible and efficient for JavaScript, and that our technique allows the enforcement of information-flow policies with almost no run-time overhead.


title: Stretching transactional memory

authors:
Aleksandar Dragojevic
Rachid Guerraoui
Michal Kapalka

abstract: Transactional memory (TM) is an appealing abstraction for programming multi-core systems. Potential target applications for TM, such as business software and video games, are likely to involve complex data structures and large transactions, requiring specific software solutions (STM). So far, however, STMs have been mainly evaluated and optimized for smaller scale benchmarks.


title: FastTrack: efficient and precise dynamic race detection

authors:
Cormac Flanagan
Stephen N. Freund

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awards: Most Influential PLDI Paper (awarded 2019)


title: Trace-based just-in-time type specialization for dynamic languages

authors:
Andreas Gal
Brendan Eich
Mike Shaver
David Anderson
David Mandelin
Mohammad R. Haghighat
Blake Kaplan
Graydon Hoare
Boris Zbarsky
Jason Orendorff
Jesse Ruderman
Edwin W. Smith
Rick Reitmaier
Michael Bebenita
Mason Chang
Michael Franz

abstract: Dynamic languages such as JavaScript are more difficult to compile than statically typed ones. Since no concrete type information is available, traditional compilers need to emit generic code that can handle all possible type combinations at runtime. We present an alternative compilation technique for dynamically-typed languages that identifies frequently executed loop traces at run-time and then generates machine code on the fly that is specialized for the actual dynamic types occurring on each path through the loop. Our method provides cheap inter-procedural type specialization, and an elegant and efficient way of incrementally compiling lazily discovered alternative paths through nested loops. We have implemented a dynamic compiler for JavaScript based on our technique and we have measured speedups of 10x and more for certain benchmark programs.


title: Control-flow refinement and progress invariants for bound analysis

authors:
Sumit Gulwani
Sagar Jain
Eric Koskinen

abstract: Symbolic complexity bounds help programmers understand the performance characteristics of their implementations. Existing work provides techniques for statically determining bounds of procedures with simple control-flow. However, procedures with nested loops or multiple paths through a single loop are challenging.


title: CEAL: a C-based language for self-adjusting computation

authors:
Matthew A. Hammer
Umut A. Acar
Yan Chen

abstract: Self-adjusting computation offers a language-centric approach to writing programs that can automatically respond to modifications to their data (e.g., inputs). Except for several domain-specific implementations, however, all previous implementations of self-adjusting computation assume mostly functional, higher-order languages such as Standard ML. Prior to this work, it was not known if self-adjusting computation can be made to work with low-level, imperative languages such as C without placing undue burden on the programmer.


title: Semantics-aware trace analysis

authors:
Kevin J. Hoffman
Patrick Eugster
Suresh Jagannathan

abstract: As computer systems continue to become more powerful and complex, so do programs. High-level abstractions introduced to deal with complexity in large programs, while simplifying human reasoning, can often obfuscate salient program properties gleaned from automated source-level analysis through subtle (often non-local) interactions. Consequently, understanding the effects of program changes and whether these changes violate intended protocols become difficult to infer. Refactorings, and feature additions, modifications, or removals can introduce hard-to-catch bugs that often go undetected until many revisions later.


title: A decision procedure for subset constraints over regular languages

authors:
Pieter Hooimeijer
Westley Weimer

abstract: Reasoning about string variables, in particular program inputs, is an important aspect of many program analyses and testing frameworks. Program inputs invariably arrive as strings, and are often manipulated using high-level string operations such as equality checks, regular expression matching, and string concatenation. It is difficult to reason about these operations because they are not well-integrated into current constraint solvers.


title: A study of memory management for web-based applications on multicore processors

authors:
Hiroshi Inoue
Hideaki Komatsu
Toshio Nakatani

abstract: More and more server workloads are becoming Web-based. In these Web-based workloads, most of the memory objects are used only during one transaction. We study the effect of the memory management approaches on the performance of such Web-based applications on two modern multicore processors. In particular, using six PHP applications, we compare a general-purpose allocator (the default allocator of the PHP runtime) and a region-based allocator, which can reduce the cost of memory management by not supporting per-object free. The region-based allocator achieves better performance for all workloads on one processor core due to its smaller memory management cost. However, when using eight cores, the region-based allocator suffers from hidden costs of increased bus traffics and the performance is reduced for many workloads by as much as 27.2% compared to the default allocator. This is because the memory bandwidth tends to become a bottleneck in systems with multicore processors.


title: A randomized dynamic program analysis technique for detecting real deadlocks

authors:
Pallavi Joshi
Chang-Seo Park
Koushik Sen
Mayur Naik

abstract: We present a novel dynamic analysis technique that finds real deadlocks in multi-threaded programs. Our technique runs in two stages. In the first stage, we use an imprecise dynamic analysis technique to find potential deadlocks in a multi-threaded program by observing an execution of the program. In the second stage, we control a random thread scheduler to create the potential deadlocks with high probability. Unlike other dynamic analysis techniques, our approach has the advantage that it does not give any false warnings. We have implemented the technique in a prototype tool for Java, and have experimented on a number of large multi-threaded Java programs. We report a number of previously known and unknown real deadlocks that were found in these benchmarks.


title: Type-based data structure verification

authors:
Ming Kawaguchi
Patrick Maxim Rondon
Ranjit Jhala

abstract: We present a refinement type-based approach for the static verification of complex data structure invariants. Our approach is based on the observation that complex data structures are typically fashioned from two elements: recursion (e.g., lists and trees), and maps (e.g., arrays and hash tables). We introduce two novel type-based mechanisms targeted towards these elements: recursive refinements and polymorphic refinements. These mechanisms automate the challenging work of generalizing and instantiating rich universal invariants by piggybacking simple refinement predicates on top of types, and carefully dividing the labor of analysis between the type system and an SMT solver. Further, the mechanisms permit the use of the abstract interpretation framework of liquid type inference to automatically synthesize complex invariants from simple logical qualifiers, thereby almost completely automating the verification. We have implemented our approach in dsolve, which uses liquid types to verify ocaml programs. We present experiments that show that our type-based approach reduces the manual annotation required to verify complex properties like sortedness, balancedness, binary-search-ordering, and acyclicity by more than an order of magnitude.


title: Proving optimizations correct using parameterized program equivalence

authors:
Sudipta Kundu
Zachary Tatlock
Sorin Lerner

abstract: Translation validation is a technique for checking that, after an optimization has run, the input and output of the optimization are equivalent. Traditionally, translation validation has been used to prove concrete, fully specified programs equivalent. In this paper we present Parameterized Equivalence Checking (PEC), a generalization of translation validation that can prove the equivalence of parameterized programs. A parameterized program is a partially specified program that can represent multiple concrete programs. For example, a parameterized program may contain a section of code whose only known property is that it does not modify certain variables. By proving parameterized programs equivalent, PEC can prove the correctness of transformation rules that represent complex optimizations once and for all, before they are ever run. We implemented our PEC technique in a tool that can establish the equivalence of two parameterized programs. To highlight the power of PEC, we designed a language for implementing complex optimizations using many-to-many rewrite rules, and used this language to implement a variety of optimizations including software pipelining, loop unrolling, loop unswitching, loop interchange, and loop fusion. Finally, to demonstrate the effectiveness of PEC, we used our PEC implementation to verify that all the optimizations we implemented in our language preserve program behavior.


title: Merlin: specification inference for explicit information flow problems

authors:
V. Benjamin Livshits
Aditya V. Nori
Sriram K. Rajamani
Anindya Banerjee

abstract: The last several years have seen a proliferation of static and runtime analysis tools for finding security violations that are caused by explicit information flow in programs. Much of this interest has been caused by the increase in the number of vulnerabilities such as cross-site scripting and SQL injection. In fact, these explicit information flow vulnerabilities commonly found in Web applications now outnumber vulnerabilities such as buffer overruns common in type-unsafe languages such as C and C++. Tools checking for these vulnerabilities require a specification to operate. In most cases the task of providing such a specification is delegated to the user. Moreover, the efficacy of these tools is only as good as the specification. Unfortunately, writing a comprehensive specification presents a major challenge: parts of the specification are easy to miss, leading to missed vulnerabilities; similarly, incorrect specifications may lead to false positives.


title: LiteRace: effective sampling for lightweight data-race detection

authors:
Daniel Marino
Madanlal Musuvathi
Satish Narayanasamy

abstract: Data races are one of the most common and subtle causes of pernicious concurrency bugs. Static techniques for preventing data races are overly conservative and do not scale well to large programs. Past research has produced several dynamic data race detectors that can be applied to large programs. They are precise in the sense that they only report actual data races. However, dynamic data race detectors incur a high performance overhead, slowing down a program's execution by an order of magnitude.


title: Parallelizing sequential applications on commodity hardware using a low-cost software transactional memory

authors:
Mojtaba Mehrara
Jeff Hao
Po-Chun Hsu
Scott A. Mahlke

abstract: Multicore designs have emerged as the mainstream design paradigm for the microprocessor industry. Unfortunately, providing multiple cores does not directly translate into performance for most applications. The industry has already fallen short of the decades-old performance trend of doubling performance every 18 months. An attractive approach for exploiting multiple cores is to rely on tools, both compilers and runtime optimizers, to automatically extract threads from sequential applications. However, despite decades of research on automatic parallelization, most techniques are only effective in the scientific and data parallel domains where array dominated codes can be precisely analyzed by the compiler. Thread-level speculation offers the opportunity to expand parallelization to general-purpose programs, but at the cost of expensive hardware support. In this paper, we focus on providing low-overhead software support for exploiting speculative parallelism. We propose STMlite, a light-weight software transactional memory model that is customized to facilitate profile-guided automatic loop parallelization. STMlite eliminates a considerable amount of checking and locking overhead in conventional software transactional memory models by decoupling the commit phase from main transaction execution. Further, strong atomicity requirements for generic transactional memories are unnecessary within a stylized automatic parallelization framework. STMlite enables sequential applications to extract meaningful performance gains on commodity multicore hardware.


title: SoftBound: highly compatible and complete spatial memory safety for c

authors:
Santosh Nagarakatte
Jianzhou Zhao
Milo M. K. Martin
Steve Zdancewic

abstract: The serious bugs and security vulnerabilities facilitated by C/C++'s lack of bounds checking are well known, yet C and C++ remain in widespread use. Unfortunately, C's arbitrary pointer arithmetic, conflation of pointers and arrays, and programmer-visible memory layout make retrofitting C/C++ with spatial safety guarantees extremely challenging. Existing approaches suffer from incompleteness, have high runtime overhead, or require non-trivial changes to the C source code. Thus far, these deficiencies have prevented widespread adoption of such techniques.


title: Safe and timely updates to multi-threaded programs

authors:
Iulian Neamtiu
Michael W. Hicks

abstract: Many dynamic updating systems have been developed that enable a program to be patched while it runs, to fix bugs or add new features. This paper explores techniques for supporting dynamic updates to multi-threaded programs, focusing on the problem of applying an update in a timely fashion while still producing correct behavior. Past work has shown that this tension of safety versus timeliness can be balanced for single-threaded programs. For multi-threaded programs, the task is more difficult because myriad thread interactions complicate understanding the possible program states to which a patch could be applied. Our approach allows the programmer to specify a few program points (e.g., one per thread) at which a patch may be applied, which simplifies reasoning about safety. To improve timeliness, a combination of static analysis and run-time support automatically expands these few points to many more that produce behavior equivalent to the originals. Experiments with thirteen realistic updates to three multi-threaded servers show that we can safely perform a dynamic update within milliseconds when more straightforward alternatives would delay some updates indefinitely.


title: Efficiently and precisely locating memory leaks and bloat

authors:
Gene Novark
Emery D. Berger
Benjamin G. Zorn

abstract: Inefficient use of memory, including leaks and bloat, remain a significant challenge for C and C++ developers. Applications with these problems become slower over time as their working set grows and can become unresponsive. At the same time, memory leaks and bloat remain notoriously difficult to debug, and comprise a large number of reported bugs in mature applications. Previous tools for diagnosing memory inefficiencies-based on garbage collection, binary rewriting, or code sampling-impose high overheads (up to 100X) or generate many false alarms.


title: Implementation of the memory-safe full ANSI-C compiler

abstract: This paper describes a completely memory-safe compiler for C language programs that is fully compatible with the ANSI C specification.


title: Progress guarantee for parallel programs via bounded lock-freedom

authors:
Erez Petrank
Madanlal Musuvathi
Bjarne Steensgaard

abstract: Parallel platforms are becoming ubiquitous with modern computing systems. Many parallel applications attempt to avoid locks in order to achieve high responsiveness, aid scalability, and avoid deadlocks and livelocks. However, avoiding the use of system locks does not guarantee that no locks are actually used, because progress inhibitors may occur in subtle ways through various program structures. Notions of progress guarantee such as lock-freedom, wait-freedom, and obstruction-freedom have been proposed in the literature to provide various levels of progress guarantees.


title: Sharing classes between families

authors:
Xin Qi
Andrew C. Myers

abstract: Class sharing is a new language mechanism for building extensible software systems. Recent work has separately explored two different kinds of extensibility: first, family inheritance, in which an entire family of related classes can be inherited, and second, adaptation, in which existing objects are extended in place with new behavior and state. Class sharing integrates these two kinds of extensibility mechanisms. With little programmer effort, objects of one family can be used as members of another, while preserving relationships among objects. Therefore, a family of classes can be adapted in place with new functionality spanning multiple classes. Object graphs can evolve from one family to another, adding or removing functionality even at run time.


title: Automatic generation of library bindings using static analysis

authors:
Tristan Ravitch
Steve Jackson
Eric Aderhold
Ben Liblit

abstract: High-level languages are growing in popularity. However, decades of C software development have produced large libraries of fast, time-tested, meritorious code that are impractical to recreate from scratch. Cross-language bindings can expose low-level C code to high-level languages. Unfortunately, writing bindings by hand is tedious and error-prone, while mainstream binding generators require extensive manual annotation or fail to offer the language features that users of modern languages have come to expect.


title: Typed self-representation

authors:
Tillmann Rendel
Klaus Ostermann
Christian Hofer

abstract: Self-representation -- the ability to represent programs in their own language -- has important applications in reflective languages and many other domains of programming language design. Although approaches to designing typed program representations for sublanguages of some base language have become quite popular recently, the question whether a fully metacircular typed self-representation is possible is still open. This paper makes a big step towards this aim by defining the Fω* calculus, an extension of the higher-order polymorphic lambda calculus Fω that allows typed self-representations. While the usability of these representations for metaprogramming is still limited, we believe that our approach makes a significant step towards a new generation of reflective languages that are both safe and efficient.


title: Laminar: practical fine-grained decentralized information flow control

authors:
Indrajit Roy
Donald E. Porter
Michael D. Bond
Kathryn S. McKinley
Emmett Witchel

abstract: Decentralized information flow control (DIFC) is a promising model for writing programs with powerful, end-to-end security guarantees. Current DIFC systems that run on commodity hardware can be broadly categorized into two types: language-level and operating system-level DIFC. Language level solutions provide no guarantees against security violations on system resources, like files and sockets. Operating system solutions can mediate accesses to system resources, but are inefficient at monitoring the flow of information through fine-grained program data structures.


title: Error propagation analysis for file systems

authors:
Cindy Rubio-González
Haryadi S. Gunawi
Ben Liblit
Remzi H. Arpaci-Dusseau
Andrea C. Arpaci-Dusseau

abstract: Unchecked errors are especially pernicious in operating system file management code. Transient or permanent hardware failures are inevitable, and error-management bugs at the file system layer can cause silent, unrecoverable data corruption. We propose an interprocedural static analysis that tracks errors as they propagate through file system code. Our implementation detects overwritten, out-of-scope, and unsaved unchecked errors. Analysis of four widely-used Linux file system implementations (CIFS, ext3, IBM JFS and ReiserFS), a relatively new file system implementation (ext4), and shared virtual file system (VFS) code uncovers 312 error propagation bugs. Our flow- and context-sensitive approach produces more precise results than related techniques while providing better diagnostic information, including possible execution paths that demonstrate each bug found.


title: Programming model for a heterogeneous x86 platform

authors:
Bratin Saha
Xiaocheng Zhou
Hu Chen
Ying Gao
Shoumeng Yan
Mohan Rajagopalan
Jesse Fang
Peinan Zhang
Ronny Ronen
Avi Mendelson

abstract: The client computing platform is moving towards a heterogeneous architecture consisting of a combination of cores focused on scalar performance, and a set of throughput-oriented cores. The throughput oriented cores (e.g. a GPU) may be connected over both coherent and non-coherent interconnects, and have different ISAs. This paper describes a programming model for such heterogeneous platforms. We discuss the language constructs, runtime implementation, and the memory model for such a programming environment. We implemented this programming environment in a x86 heterogeneous platform simulator. We ported a number of workloads to our programming environment, and present the performance of our programming environment on these workloads.


title: Verifiable composition of deterministic grammars

authors:
August Schwerdfeger
Eric Van Wyk

abstract: There is an increasing interest in extensible languages,


title: Chameleon: adaptive selection of collections

authors:
Ohad Shacham
Martin T. Vechev
Eran Yahav

abstract: Languages such as Java and C#, as well as scripting languages like Python, and Ruby, make extensive use of Collection classes. A collection implementation represents a fixed choice in the dimensions of operation time, space utilization, and synchronization. Using the collection in a manner not consistent with this fixed choice can cause significant performance degradation. In this paper, we present CHAMELEON, a low-overhead automatic tool that assists the programmer in choosing the appropriate collection implementation for her application. During program execution, CHAMELEON computes elaborate trace and heap-based metrics on collection behavior. These metrics are consumed on-thefly by a rules engine which outputs a list of suggested collection adaptation strategies. The tool can apply these corrective strategies automatically or present them to the programmer. We have implemented CHAMELEON on top of a IBM's J9 production JVM, and evaluated it over a small set of benchmarks. We show that for some applications, using CHAMELEON leads to a significant improvement of the memory footprint of the application.


title: Program verification using templates over predicate abstraction

authors:
Saurabh Srivastava
Sumit Gulwani

abstract: We address the problem of automatically generating invariants with quantified and boolean structure for proving the validity of given assertions or generating pre-conditions under which the assertions are valid. We present three novel algorithms, having different strengths, that combine template and predicate abstraction based formalisms to discover required sophisticated program invariants using SMT solvers.


title: Dynamic software updates: a VM-centric approach

authors:
Suriya Subramanian
Michael W. Hicks
Kathryn S. McKinley

abstract: Software evolves to fix bugs and add features. Stopping and restarting programs to apply changes is inconvenient and often costly. Dynamic software updating (DSU) addresses this problem by updating programs while they execute, but existing DSU systems for managed languages do not support many updates that occur in practice and are inefficient. This paper presents the design and implementation of Jvolve, a DSU-enhanced Java VM. Updated programs may add, delete, and replace fields and methods anywhere within the class hierarchy. Jvolve implements these updates by adding to and coordinating VM classloading, just-in-time compilation, scheduling, return barriers, on-stack replacement, and garbage collection. Jvolve, is safe: its use of bytecode verification and VM thread synchronization ensures that an update will always produce type-correct executions. Jvolve is flexible: it can support 20 of 22 updates to three open-source programs--Jetty web server, JavaEmailServer, and CrossFTP server--based on actual releases occurring over 1 to 2 years. Jvolve is efficient: performance experiments show that incurs no overhead during steady-state execution. These results demonstrate that this work is a significant step towards practical support for dynamic updates in virtual machines for managed languages.


title: Binary analysis for measurement and attribution of program performance

authors:
Nathan R. Tallent
John M. Mellor-Crummey
Michael W. Fagan

abstract: Modern programs frequently employ sophisticated modular designs. As a result, performance problems cannot be identified from costs attributed to routines in isolation; understanding code performance requires information about a routine's calling context. Existing performance tools fall short in this respect. Prior strategies for attributing context-sensitive performance at the source level either compromise measurement accuracy, remain too close to the binary, or require custom compilers. To understand the performance of fully optimized modular code, we developed two novel binary analysis techniques: 1) on-the-fly analysis of optimized machine code to enable minimally intrusive and accurate attribution of costs to dynamic calling contexts; and 2) post-mortem analysis of optimized machine code and its debugging sections to recover its program structure and reconstruct a mapping back to its source code. By combining the recovered static program structure with dynamic calling context information, we can accurately attribute performance metrics to calling contexts, procedures, loops, and inlined instances of procedures. We demonstrate that the fusion of this information provides unique insight into the performance of complex modular codes. This work is implemented in the HPCToolkit performance tools (http://hpctoolkit.org).


title: Analyzing recursive programs using a fixed-point calculus

authors:
Salvatore La Torre
Parthasarathy Madhusudan
Gennaro Parlato

abstract: We show that recursive programs where variables range over finite domains can be effectively and efficiently analyzed by describing the analysis algorithm using a formula in a fixed-point calculus. In contrast with programming in traditional languages, a fixed-point calculus serves as a high-level programming language to easily, correctly, and succinctly describe model-checking algorithms While there have been declarative high-level formalisms that have been proposed earlier for analysis problems (e.g., Datalog the fixed-point calculus we propose has the salient feature that it also allows algorithmic aspects to be specified.


title: Towards a holistic approach to auto-parallelization: integrating profile-driven parallelism detection and machine-learning based mapping

authors:
Georgios Tournavitis
Zheng Wang
Björn Franke
Michael F. P. O'Boyle

abstract: Compiler-based auto-parallelization is a much studied area, yet has still not found wide-spread application. This is largely due to the poor exploitation of application parallelism, subsequently resulting in performance levels far below those which a skilled expert programmer could achieve. We have identified two weaknesses in traditional parallelizing compilers and propose a novel, integrated approach, resulting in significant performance improvements of the generated parallel code. Using profile-driven parallelism detection we overcome the limitations of static analysis, enabling us to identify more application parallelism and only rely on the user for final approval. In addition, we replace the traditional target-specific and inflexible mapping heuristics with a machine-learning based prediction mechanism, resulting in better mapping decisions while providing more scope for adaptation to different target architectures. We have evaluated our parallelization strategy against the NAS and SPEC OMP benchmarks and two different multi-core platforms (dual quad-core Intel Xeon SMP and dual-socket QS20 Cell blade). We demonstrate that our approach not only yields significant improvements when compared with state-of-the-art parallelizing compilers, but comes close to and sometimes exceeds the performance of manually parallelized codes. On average, our methodology achieves 96% of the performance of the hand-tuned OpenMP NAS and SPEC parallel benchmarks on the Intel Xeon platform and gains a significant speedup for the IBM Cell platform, demonstrating the potential of profile-guided and machine-learning based parallelization for complex multi-core platforms.


title: TAJ: effective taint analysis of web applications

authors:
Omer Tripp
Marco Pistoia
Stephen J. Fink
Manu Sridharan
Omri Weisman

abstract: Taint analysis, a form of information-flow analysis, establishes whether values from untrusted methods and parameters may flow into security-sensitive operations. Taint analysis can detect many common vulnerabilities in Web applications, and so has attracted much attention from both the research community and industry. However, most static taint-analysis tools do not address critical requirements for an industrial-strength tool. Specifically, an industrial-strength tool must scale to large industrial Web applications, model essential Web-application code artifacts, and generate consumable reports for a wide range of attack vectors.


title: Verified validation of lazy code motion

authors:
Jean-Baptiste Tristan
Xavier Leroy

abstract: Translation validation establishes a posteriori the correctness of a run of a compilation pass or other program transformation. In this paper, we develop an efficient translation validation algorithm for the Lazy Code Motion (LCM) optimization. LCM is an interesting challenge for validation because it is a global optimization that moves code across loops. Consequently, care must be taken not to move computations that may fail before loops that may not terminate. Our validator includes a specific check for anticipability to rule out such incorrect moves. We present a mechanically-checked proof of correctness of the validation algorithm, using the Coq proof assistant. Combining our validator with an unverified implementation of LCM, we obtain a LCM pass that is provably semantics-preserving and was integrated in the CompCert formally verified compiler.


title: Go with the flow: profiling copies to find runtime bloat

authors:
Guoqing Xu
Matthew Arnold
Nick Mitchell
Atanas Rountev
Gary Sevitsky

abstract: Many large-scale Java applications suffer from runtime bloat. They execute large volumes of methods, and create many temporary objects, all to execute relatively simple operations. There are large opportunities for performance optimizations in these applications, but most are being missed by existing optimization and tooling technology. While JIT optimizations struggle for a few percent, performance experts analyze deployed applications and regularly find gains of 2x or more.


title: An integrated proof language for imperative programs

authors:
Karen Zee
Viktor Kuncak
Martin C. Rinard

abstract: We present an integrated proof language for guiding the actions of multiple reasoning systems as they work together to prove complex correctness properties of imperative programs. The language operates in the context of a program verification system that uses multiple reasoning systems to discharge generated proof obligations. It is designed to 1) enable developers to resolve key choice points in complex program correctness proofs, thereby enabling automated reasoning systems to successfully prove the desired correctness properties; 2) allow developers to identify key lemmas for the reasoning systems to prove, thereby guiding the reasoning systems to find an effective proof decomposition; 3) enable multiple reasoning systems to work together productively to prove a single correctness property by providing a mechanism that developers can use to divide the property into lemmas, each of which is suitable for a different reasoning system; and 4) enable developers to identify specific lemmas that the reasoning systems should use when attempting to prove other lemmas or correctness properties, thereby appropriately confining the search space so that the reasoning systems can find a proof in an acceptable amount of time.