Precision-guided context sensitivity for pointer analysis

Context sensitivity is an essential technique for ensuring high precision in Java pointer analyses. It has been observed that applying context sensitivity partially, only on a select subset of the methods, can improve the balance between analysis precision and speed. However, existing techniques are based on heuristics that do not provide much insight into what characterizes this method subset. In this work, we present a more principled approach for identifying precision-critical methods, based on general patterns of value flows that explain where most of the imprecision arises in context-insensitive pointer analysis. Accordingly, we provide an efficient algorithm to recognize these flow patterns in a given program and exploit them to yield good tradeoffs between analysis precision and speed. Our experimental results on standard benchmark and real-world programs show that a pointer analysis that applies context sensitivity partially, only on the identified precision-critical methods, preserves effectively all (98.8%) of the precision of a highly-precise conventional context-sensitive pointer analysis (2-object-sensitive with a context-sensitive heap), with a substantial speedup (on average 3.4X, and up to 9.2X)

Scalability-First Pointer Analysis with Self-Tuning Context-Sensitivity

Context-sensitivity is important in pointer analysis to ensure high precision, but existing techniques suffer from unpredictable scala- bility. Many variants of context-sensitivity exist, and it is difficult to choose one that leads to reasonable analysis time and obtains high precision, without running the analysis multiple times. We present the Scaler framework that addresses this problem. Scaler efficiently estimates the amount of points-to information that would be needed to analyze each method with different variants of context-sensitivity. It then selects an appropriate variant for each method so that the total amount of points-to information is bounded, while utilizing the available space to maximize precision. Our experimental results demonstrate that Scaler achieves pre- dictable scalability for all the evaluated programs (e.g., speedups can reach 10x for 2-object-sensitivity), while providing a precision that matches or even exceeds that of the best alternative techniques

Subheap-Augmented Garbage Collection

Automated memory management avoids the tedium and danger of manual techniques. However, as no programmer input is required, no widely available interface exists to permit principled control over sometimes unacceptable performance costs. This dissertation explores the idea that performance-oriented languages should give programmers greater control over where and when the garbage collector (GC) expends effort. We describe an interface and implementation to expose heap partitioning and collection decisions without compromising type safety. We show that our interface allows the programmer to encode a form of reference counting using Hayes\u27 notion of key objects. Preliminary experimental data suggests that our proposed mechanism can avoid high overheads suffered by tracing collectors in some scenarios, especially with tight heaps. However, for other applications, the costs of applying subheaps---in human effort and runtime overheads---remain daunting

Study of optimal design of 3D mechanical metamaterials

This thesis aims to develop and extend numerical methods for solving the elastic problem in 2D to a 3D solution. The primary objective is to investigate and identify the modifications and extensions necessary to adapt existing techniques used in 2D to a 3D framework. The focus is on developing a robust and efficient numerical method that accurately models the behavior of elastic materials in three dimensions. The study encompasses several objectives to achieve a comprehensive understanding of 3D material design and topology optimization in the context of mechanical metamaterials. Firstly, an introduction to topology optimization is provided, including the formulation and regularization of the problem, and an explanation of density-based and the Level Set method. The thesis further investigates the SWAN repository’s code, an object-oriented Matlab software, assessing its applicability for conducting simulations. The thesis explores the optimization of both normal materials and metamaterials microstructures. For normal materials, a comparison is made between different optimization approaches, specifically the MMA optimizer utilizing a densitybased method and the Null Space optimizer employing a level set-based method. Additionally, the impact of varying final volume fractions on the optimization outcomes is studied. This investigation provides valuable insights into the influence of different parameter variations on the resulting microstructures and optimization performance. Furthermore, the study focuses on metamaterials microstructures and explores their optimization using the Null Space optimizer, and different α and β values are employed to examine their effects on the final design. The optimization process is also conducted for different final volume fractions to evaluate the influence of volume fraction on metamaterial performance. This study on material design and topology optimization has yielded several important conclusions: the simulations showcased the relationship between dimensionality and convergence speed, with 2D simulations demonstrating faster convergence compared to 3D simulations; analysis of parameters such as the cost function and the number of iterations has been conducted comparing different optimizers, it has been highlighted the challenges and unique considerations involved in optimizing metamaterials; and, overall, the research has contributed to the understanding of optimization processes and the generation of innovative material configurations

Text Summarization Across High and Low-Resource Settings

Natural language processing aims to build automated systems that can both understand and generate natural language textual data. As the amount of textual data available online has increased exponentially, so has the need for intelligence systems to comprehend and present it to the world. As a result, automatic text summarization, the process by which a text\u27s salient content is automatically distilled into a concise form, has become a necessary tool. Automatic text summarization approaches and applications vary based on the input summarized, which may constitute single or multiple documents of different genres. Furthermore, the desired output style may consist of a sentence or sub-sentential units chosen directly from the input in extractive summarization or a fusion and paraphrase of the input document in abstractive summarization. Despite differences in the above use-cases, specific themes, such as the role of large-scale data for training these models, the application of summarization models in real-world scenarios, and the need for adequately evaluating and comparing summaries, are common across these settings. This dissertation presents novel data and modeling techniques for deep neural network-based summarization models trained across high-resource (thousands of supervised training examples) and low-resource (zero to hundreds of supervised training examples) data settings and a comprehensive evaluation of the model and metric progress in the field. We examine both Recurrent Neural Network (RNN)-based and Transformer-based models to extract and generate summaries from the input. To facilitate the training of large-scale networks, we introduce datasets applicable for multi-document summarization (MDS) for pedagogical applications and for news summarization. While the high-resource settings allow models to advance state-of-the-art performance, the failure of such models to adapt to settings outside of that in which it was initially trained requires smarter use of labeled data and motivates work in low-resource summarization. To this end, we propose unsupervised learning techniques for both extractive summarization in question answering, abstractive summarization on distantly-supervised data for summarization of community question answering forums, and abstractive zero and few-shot summarization across several domains. To measure the progress made along these axes, we revisit the evaluation of current summarization models. In particular, this dissertation addresses the following research objectives: 1) High-resource Summarization. We introduce datasets for multi-document summarization, focusing on pedagogical applications for NLP, news summarization, and Wikipedia topic summarization. Large-scale datasets allow models to achieve state-of-the-art performance on these tasks compared to prior modeling techniques, and we introduce a novel model to reduce redundancy. However, we also examine how models trained on these large-scale datasets fare when applied to new settings, showing the need for more generalizable models. 2) Low-resource Summarization. While high-resource summarization improves model performance, for practical applications, data-efficient models are necessary. We propose a pipeline for creating synthetic training data for training extractive question-answering models, a form of query-based extractive summarization with short-phrase summaries. In other work, we propose an automatic pipeline for training a multi-document summarizer in answer summarization on community question-answering forums without labeled data. Finally, we push the boundaries of abstractive summarization model performance when little or no training data is available across several domains. 3) Automatic Summarization Evaluation. To understand the extent of progress made across recent modeling techniques and better understand the current evaluation protocols, we examine the current metrics used to compare summarization output quality across 12 metrics across 23 deep neural network models and propose better-motivated summarization evaluation guidelines as well as point to open problems in summarization evaluation

Service Abstractions for Scalable Deep Learning Inference at the Edge

Deep learning driven intelligent edge has already become a reality, where millions of mobile, wearable, and IoT devices analyze real-time data and transform those into actionable insights on-device. Typical approaches for optimizing deep learning inference mostly focus on accelerating the execution of individual inference tasks, without considering the contextual correlation unique to edge environments and the statistical nature of learning-based computation. Specifically, they treat inference workloads as individual black boxes and apply canonical system optimization techniques, developed over the last few decades, to handle them as yet another type of computation-intensive applications. As a result, deep learning inference on edge devices still face the ever increasing challenges of customization to edge device heterogeneity, fuzzy computation redundancy between inference tasks, and end-to-end deployment at scale. In this thesis, we propose the first framework that automates and scales the end-to-end process of deploying efficient deep learning inference from the cloud to heterogeneous edge devices. The framework consists of a series of service abstractions that handle DNN model tailoring, model indexing and query, and computation reuse for runtime inference respectively. Together, these services bridge the gap between deep learning training and inference, eliminate computation redundancy during inference execution, and further lower the barrier for deep learning algorithm and system co-optimization. To build efficient and scalable services, we take a unique algorithmic approach of harnessing the semantic correlation between the learning-based computation. Rather than viewing individual tasks as isolated black boxes, we optimize them collectively in a white box approach, proposing primitives to formulate the semantics of the deep learning workloads, algorithms to assess their hidden correlation (in terms of the input data, the neural network models, and the deployment trials) and merge common processing steps to minimize redundancy

Scalable Logic Defined Static Analysis

Logic languages such as Datalog have been proposed as a method for specifying flexible and customisable static analysers. Using Datalog, various classes of static analyses can be expressed precisely and succinctly, requiring fewer lines of code than hand-crafted analysers. In this paradigm, a static analysis specification is encoded by a set of declarative logic rules and an o -the-shelf solver is used to compute the result of the static analysis. Unfortunately, when large-scale analyses are employed, Datalog-based tools currently fail to scale in comparison to hand-crafted static analysers. As a result, Datalog-based analysers have largely remained an academic curiosity, rather than industrially respectful tools. This thesis outlines our e orts in understanding the sources of performance limitations in Datalog-based tools. We propose a novel evaluation technique that is predicated on the fact that in the case of static analysis, the logical specification is a design time artefact and hence does not change during evaluation. Thus, instead of directly evaluating Datalog rules, our approach leverages partial evaluation to synthesise a specialised static analyser from these rules. This approach enables a novel indexing optimisations that automatically selects an optimal set of indexes to speedup and minimise memory usage in the Datalog computation. Lastly, we explore the case of more expressive logics, namely, constrained Horn clause and their use in proving the correctness of programs. We identify a bottleneck in various symbolic evaluation algorithms that centre around Craig interpolation. We propose a method of improving these evaluation algorithms by a proposing a method of guiding theorem provers to discover relevant interpolants with respect to the input logic specification. The culmination of our work is implemented in a general-purpose and highperformance tool called Souffl´e. We describe Souffl´e and evaluate its performance experimentally, showing significant improvement over alternative techniques and its scalability in real-world industrial use cases

Computational automation for efficient design of acoustic metamaterials

Acoustic metamaterials (AMMs) are an exciting technology because they are capable of responding to vibrations in ways that are impossible to achieve with conventional materials. However, realization of AMMs requires engineering design to provide a connection between first-principles research and production of parts that perform as expected. Designing AMMs is a challenging endeavor because evaluating designs is costly and manufacturing metamaterials requires precise techniques with small minimum resolutions. To address these challenges, new computational tools are necessary to aid design. This work proposes three tasks that improve the capabilities of design for AMM while being extensible to other engineering design automation tasks. The first task is to develop a design exploration tool that improves the computational efficiency of identifying sets of high-performing designs in a design space that is sparse and comprises mixed discrete/continuous data. The second task is to develop a process for designers to evaluate manufacturability of difficult-to-manufacture parts and drive co-development of manufacturing methods and AMM. In the final task, a machine learning based method is developed to efficiently model AMM with heterogeneous arrangements of their microstructures such that strict homogenization is infeasible. The outcomes from completing these tasks will provide a significant and novel improvement over existing methods of designing AMMs.Mechanical Engineerin

End-to-end deep reinforcement learning in computer systems

Abstract The growing complexity of data processing systems has long led systems designers to imagine systems (e.g. databases, schedulers) which can self-configure and adapt based on environmental cues. In this context, reinforcement learning (RL) methods have since their inception appealed to systems developers. They promise to acquire complex decision policies from raw feedback signals. Despite their conceptual popularity, RL methods are scarcely found in real-world data processing systems. Recently, RL has seen explosive growth in interest due to high profile successes when utilising large neural networks (deep reinforcement learning). Newly emerging machine learning frameworks and powerful hardware accelerators have given rise to a plethora of new potential applications. In this dissertation, I first argue that in order to design and execute deep RL algorithms efficiently, novel software abstractions are required which can accommodate the distinct computational patterns of communication-intensive and fast-evolving algorithms. I propose an architecture which decouples logical algorithm construction from local and distributed execution semantics. I further present RLgraph, my proof-of-concept implementation of this architecture. In RLgraph, algorithm developers can explore novel designs by constructing a high-level data flow graph through combination of logical components. This dataflow graph is independent of specific backend frameworks or notions of execution, and is only later mapped to execution semantics via a staged build process. RLgraph enables high-performing algorithm implementations while maintaining flexibility for rapid prototyping. Second, I investigate reasons for the scarcity of RL applications in systems themselves. I argue that progress in applied RL is hindered by a lack of tools for task model design which bridge the gap between systems and algorithms, and also by missing shared standards for evaluation of model capabilities. I introduce Wield, a first-of-its-kind tool for incremental model design in applied RL. Wield provides a small set of primitives which decouple systems interfaces and deployment-specific configuration from representation. Core to Wield is a novel instructive experiment protocol called progressive randomisation which helps practitioners to incrementally evaluate different dimensions of non-determinism. I demonstrate how Wield and progressive randomisation can be used to reproduce and assess prior work, and to guide implementation of novel RL applications

Quantum Many-Body Dynamics of Atomic Systems for Quantum Simulation and Metrology

Understanding the physics of quantum many-body systems poses a significant challenge in quantum science. These systems, when precisely controlled, have the potential to enable a new generation of quantum technology, encompassing powerful computing devices, simulators for studying complex models in condensed matter physics, and advanced sensors for probing new physical regimes with unprecedented precision. However, despite rapid progress in the development of atomic platforms for these applications, we are now venturing into a realm where we can access physics beyond our current computational capabilities. This presents a challenge to further unraveling and characterizing the intricate physics realizable within these systems, and designing improved control techniques to exploit their full potential. The demands to bridge this gap between cutting-edge experiments and our theoretical understanding are steep. Such systems often involve hundreds to thousands of particles, with varying numbers of internal and external degrees of freedom, as well as features including environmental couplings, disorder, or long-ranged interactions. In this thesis, we develop and apply a range of computational tools, including exact methods, tensor networks, and phase space approaches to model these systems. On their own, each of these methods has its own limitations, but a resourceful combination of them offers a promising computational approach to modeling various nonequilibrium phenomena and to building a cohesive picture of the involved physics. We employ this hybrid approach to explore the dynamical creation of quantum correlations in a range of many-body models relevant to current atomic platforms such as trapped ions, as well as neutral atoms trapped in either optical lattices or arrays of optical tweezers. Additionally, in some instances, we supplement our theoretical and computational investigations with experimental data, further enriching our understanding of both the underlying physics and the applicability of the tools we employ. We commence by reviewing recent progress into the development of controllable atomic platforms and the various numerical techniques employed throughout the thesis. We then consider three broad classes of physical models: Fermi-Hubbard systems, realizable with fermionic atoms trapped in optical lattices; spin-boson models, such as the Dicke model, achievable in trapped ion or cavity experiments; and quantum spin models with varying dependence on the inter-atomic distance, accessible in trapped ions, arrays of Rydberg atoms, and magnetic dipoles. For each model, we develop schemes both to generate useful entanglement that can be utilized by current state-of the-art atomic clocks and sensors as well as to investigate fundamental aspects of the many-body dynamics. Finally, we consider separate protocols to access information about the quantum wavefunction beyond the conventional paradigm of simple one- or two-body observables. This includes experimental results for tomography of a single trapped atom, and a theoretical proposal to access multi-particle coherences for examining equilibrium quantum phase transitions. In each of our studies, we bring elements of our computational toolbox to bear, in addition to a diverse of range of theoretical analyses and, in some instances, experimental results. Our ultimate goal is to validate the inherent physics of these platforms, develop new insights into dynamical quantum many-body phenomena, and create noise-robust protocols for future quantum sensors, which may one day enable investigations of fundamental physics beyond the current Standard Model.</p