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1. An Interactive Debugger for Rust Trait Errors

   https://doi.org/10.1145/3729302  

   Gray, Gavin; Crichton, Will; Krishnamurthi, Shriram (June 2025, Proceedings of the ACM on Programming Languages)

   Compiler diagnostics for type inference failures are notoriously bad, and type classes only make the problem worse. By introducing a complex search process during inference, type classes can lead to wholly inscrutable or useless errors. We describe a system, Argus, for interactively visualizing type class inferences to help programmers debug inference failures, applied specifically to Rust’s trait system. The core insight of Argus is to avoid the traditional model of compiler diagnostics as one-size-fits-all, instead providing the programmer with different views on the search tree corresponding to different debugging goals. Argus carefully uses defaults to improve debugging productivity, including interface design (e.g., not showing full paths of types by default) and heuristics (e.g., sorting obligations based on the expected complexity of fixing them). We evaluated Argus in a user study whereN= 25 participants debugged type inference failures in realistic Rust programs, finding that participants using Argus correctly localized 2.2× as many faults and localized 3.3× faster compared to not using Argus. 

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2. Static Program Reduction via Type-Directed Slicing

   https://doi.org/10.1145/3728968  

   Nguyen, Loi Ngo_Duc; Islam, Tahiatul; Wang, Theron; Lenz, Sam; Kellogg, Martin (June 2025, Proceedings of the ACM on Software Engineering)

   A traditional program slicer constructs a smaller variant of a target program that computes the same result with respect to some target variable—that is, program slicing preserves the original program’srun-time semantics. We proposetype-directed slicing, which constructs a smaller program that guarantees that a typechecker will produce the same result on the sliced program when considering only a target program location—that is, a type-directed slicer preserves the target program’scompile-time semantics, from the view of a specific typechecker, with respect to some location. Type-directed slicing is a useful debugging aid for designers and maintainers of typecheckers. When a typechecker produces an unexpected result (a crash, a false positive warning, a missed warning, etc.) on a large codebase, the user typically reports a bug to the maintainers of the typechecker without an accompanying test case. State-of-the-art approaches to thisprogram reduction problemare dynamic: they require repeatedly running the typechecker to validate minimizations. A type-directed slicer solves this problem statically, without rerunning the typechecker, by exploiting the modularity inherent in a typechecker’s type rules. Our prototype type-directed slicer for Java is fully automatic, can operate on incomplete programs, and is fast. It produces a small test case that preserves typechecker misbehavior for 25 of 28 (89%) historical bugs from the issue trackers of three widely-used typecheckers: the Java compiler itself, NullAway, and the Checker Framework; in each of these 25 cases, it preserved the typechecker’s behavior even without the classpath of the target program. And, it runs in under a minute on each benchmark, whose size ranges up to millions of lines of code, on a free-tier CI runner. 

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3. Holistic Optimization Framework for FPGA Accelerators

   https://doi.org/10.1145/3769307  

   Pouget, Stéphane; Lo, Michael; Pouchet, Louis-Noël; Cong, Jason (November 2025, ACM Transactions on Design Automation of Electronic Systems)

   Customized accelerators have revolutionized modern computing by delivering substantial gains in energy efficiency and performance through hardware specialization. Field-Programmable Gate Arrays (FPGAs) play a crucial role in this paradigm, offering unparalleled flexibility and high-performance potential. High-Level Synthesis (HLS) and source-to-source compilers have simplified FPGA development by translating high-level programming languages into hardware descriptions enriched with directives. However, achieving high Quality of Results (QoR) remains a significant challenge, requiring intricate code transformations, strategic directive placement, and optimized data communication. This article presentsPrometheus, a holistic optimization framework that integrates key optimizations - includingtask fusion, tiling, loop permutation, computation-communication overlap, and concurrent task execution-into a unified design space. By leveragingNon-Linear Programming (NLP) methodologies, Prometheus explores the optimization space under strict resource constraints, enabling automatic bitstream generation. Unlike existing frameworks, Prometheus considers interdependent transformations and dynamically balances computation and memory access. We evaluate Prometheus across multiple benchmarks, demonstrating its ability to maximize parallelism, minimize execution stalls, and optimize data movement. The results showcase its superior performance compared to state-of-the-art FPGA optimization frameworks, highlighting its effectiveness in delivering high QoR while reducing manual tuning efforts. 

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4. Debugging and Detecting Numerical Errors in Computation with Posits

   https://doi.org/10.1145/3385412.3386004  

   Chowdhary, Sangeeta; Lim, Jay P; Nagarakatte, Santosh (July 2020, 2020 ACM SIGPLAN Conference on Programming Language Design and Implementation (PLDI-2020))

   Posit is a recently proposed alternative to the floating point representation (FP). It provides tapered accuracy. Given a fixed number of bits, the posit representation can provide better precision for some numbers compared to FP, which has generated significant interest in numerous domains. Being a representation with tapered accuracy, it can introduce high rounding errors for numbers outside the above golden zone. Programmers currently lack tools to detect and debug errors while programming with posits. This paper presents PositDebug, a compile-time instrumentation that performs shadow execution with high pre- cision values to detect various errors in computation using posits. To assist the programmer in debugging the reported error, PositDebug also provides directed acyclic graphs of instructions, which are likely responsible for the error. A contribution of this paper is the design of the metadata per memory location for shadow execution that enables productive debugging of errors with long-running programs. We have used PositDebug to detect and debug errors in various numerical applications written using posits. To demonstrate that these ideas are applicable even for FP programs, we have built a shadow execution framework for FP programs that is an order of magnitude faster than Herbgrind. 

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5. Global phylogeography and microdiversity of the marine diazotrophic photoautotrophs Trichodesmium and UCYN-A

   https://doi.org/10.1128/msphere.00245-25  

   Nguyen, Angie; Ustick, Lucas J; Larkin, Alyse A; Martiny, Adam C (July 2025, mSphere)

   Campbell, Barbara J (Ed.)

   ABSTRACT Photoautotrophic diazotrophs, specifically the generaTrichodesmiumand UCYN-A, play a pivotal role in marine nitrogen cycling through their capacity for nitrogen fixation. Despite their global distribution, the microdiversity and environmental drivers of these diazotrophs remain underexplored. This study provides a comprehensive analysis of the global diversity and distribution ofTrichodesmiumand UCYN-A using the nitrogenase gene (nifH) as a genetic marker. We sequenced 954 samples from the Pacific, Atlantic, and Indian Oceans as part of the Bio-GO-SHIP project. Our results reveal significant phylogenetic and biogeographic differences between and within the two genera.Trichodesmiumexhibited greater microdiversity compared to UCYN-A, with clades showing region-specific distribution.Trichodesmiumclades were primarily influenced by temperature and nutrient availability. They were particularly frequent in regions of phosphorus stress. In contrast, UCYN-A was most frequently observed in regions experiencing iron stress. UCYN-A clades demonstrated more homogeneous distributions, with a single sequence variant within the UCYN-A1 clade dominating across varied environments. The biogeographic patterns and environmental correlations ofTrichodesmiumand UCYN-A highlight the role of microdiversity in their ecological adaptation and reflect their different ecological strategies. These findings underscore the importance of characterizing the global patterns of fine-scale genetic diversity to better understand the functional roles and distribution of marine nitrogen-fixing photoautotrophs.IMPORTANCEThis study provides insights into the global diversity and distribution of nitrogen-fixing photoautotrophs, specificallyTrichodesmiumand UCYN-A. We sequenced 954 oceanic samples of thenifHnitrogenase gene and uncovered significant differences in microdiversity and environmental associations between these genera.Trichodesmiumshowed high levels of sequence diversity and region-specific clades influenced by temperature and nutrient availability. In contrast, UCYN-A exhibited a more uniform distribution, thriving in iron-stressed regions. Quantifying these fine-scale genetic variations enhances our knowledge of their ecological roles and adaptations, emphasizing the need to characterize the genetic diversity of marine nitrogen-fixing prokaryotes. 

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