Petros Maniatis
Petros Maniatis is a Senior Staff Research Scientist at Google DeepMind, in the Learning for Code Team. Prior to that, he was a Senior Research Scientist at Intel Labs, working in Intel's Berkeley Research Lab and then at the Intel Science and Technology Center on Secure Computing at UC Berkeley. He received his MSc and Ph.D. from the Computer Science Department at Stanford University. Before Stanford, he obtained his BSc with honors at the Department of Informatics of the University of Athens in Greece. His current research interests lie primarily in the confluence of machine learning and software engineering.
Authored Publications
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CodeQueries: A Dataset of Semantic Queries over Code
Surya Prakash Sahu
Madhurima Mandal
Shikhar Bharadwaj
Aditya Kanade
Shirish Shevade
Innovations in Software Engineering (ISEC), ACM, Bangalore, India(2024)
Preview abstract
Developers often have questions about semantic aspects of code
they are working on, e.g., “Is there a class whose parent classes
declare a conflicting attribute?”. Answering them requires understanding code semantics such as attributes and inheritance relation
of classes. An answer to such a question should identify code spans
constituting the answer (e.g., the declaration of the subclass) as well
as supporting facts (e.g., the definitions of the conflicting attributes).
The existing work on question-answering over code has considered
yes/no questions or method-level context. We contribute a labeled
dataset, called CodeQueries, of semantic queries over Python code.
Compared to the existing datasets, in CodeQueries, the queries
are about code semantics, the context is file level and the answers
are code spans. We curate the dataset based on queries supported
by a widely-used static analysis tool, CodeQL, and include both
positive and negative examples, and queries requiring single-hop
and multi-hop reasoning.
To assess the value of our dataset, we evaluate baseline neural
approaches. We study a large language model (GPT3.5-Turbo) in
zero-shot and few-shot settings on a subset of CodeQueries. We
also evaluate a BERT style model (CuBERT) with fine-tuning. We
find that these models achieve limited success on CodeQueries.
CodeQueries is thus a challenging dataset to test the ability of
neural models, to understand code semantics, in the extractive
question-answering setting
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Resolving Code Review Comments with Machine Learning
Alexander Frömmgen
Peter Choy
Elena Khrapko
Pierre-Antoine Manzagol
Marcus Revaj
2024 IEEE/ACM 46th International Conference on Software Engineering: Software Engineering in Practice (ICSE-SEIP) (to appear)
Preview abstract
Code reviews are a critical part of the software development process, taking a significant amount of the code authors’ and the code reviewers’ time. As part of this process, the reviewer inspects the proposed code and asks the author for code changes through comments written in natural language. At Google, we see millions of reviewer comments per year, and authors require an average of ∼60 minutes active shepherding time between sending changes for review and finally submitting the change. In our measurements, the required active work time that the code author must devote to address reviewer comments grows almost linearly with the number of comments. However, with machine learning (ML), we have an opportunity to automate and streamline the code-review process, e.g., by proposing code changes based on a comment’s text.
We describe our application of recent advances in large sequence models in a real-world setting to automatically resolve code-review comments in the day-to-day development workflow at Google. We present the evolution of this feature from an asynchronous generation of suggested edits after the reviewer sends feedback, to an interactive experience that suggests code edits to the reviewer at review time. In deployment, code-change authors at Google address 7.5% of all reviewer comments by applying an ML-suggested edit. The impact of this will be to reduce the time spent on code reviews by hundreds of thousands of engineer hours annually at Google scale. Unsolicited, very positive feedback highlights that the impact of ML-suggested code edits increases Googlers’ productivity and allows them to focus on more creative and complex tasks.
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Snowcat: Efficient Kernel Concurrency Testing using a Learned Coverage Predictor
Sishuai Gong
Dinglan Peng
Pedro Fonseca
Symposium on Operating Systems Principles (SOSP)(2023)
Preview abstract
Random-based approaches and heuristics are commonly
used in kernel concurrency testing due to the massive scale
of modern kernels and corresponding interleaving space.
The lack of accurate and scalable approaches to analyze concurrent
kernel executions makes existing testing approaches
heavily rely on expensive dynamic executions to measure
the effectiveness of a new test. Unfortunately, the high cost
incurred by dynamic executions limits the breadth of the
exploration and puts latency pressure on finding effective
concurrent test inputs and schedules, hindering the overall
testing effectiveness.
This paper proposes Snowcat, a kernel concurrency testing
framework that generates effective test inputs and schedules
using a learned kernel block-coverage predictor. Using a
graph neural network, the coverage predictor takes a concurrent
test input and scheduling hints and outputs a prediction
on whether certain important code blocks will be executed.
Using this predictor, Snowcat can skip concurrent tests that
are likely to be fruitless and prioritize the promising ones
for actual dynamic execution.
After testing the Linux kernel for over a week, Snowcat
finds ∼17% more potential data races, by prioritizing tests of
more fruitful schedules than existing work would have chosen.
Snowcat can also find effective test inputs that expose
new concurrency bugs with higher probability (1.4×∼2.6×),
or reproduce known bugs more quickly (15×) than state-ofart
testing tools. More importantly, Snowcat is shown to be
more efficient at reaching a desirable level of race coverage
in the continuous setting, as the Linux kernel evolves from
version to version. In total, Snowcat discovered 17 new concurrency
bugs in Linux kernel 6.1, of which 13 are confirmed
and 6 are fixed.
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Predicting Dynamic Properties of Heap Allocations Using Neural Networks Trained on Static Code
Christian Navasca
Martin Maas
Guoqing Harry Xu
2023 ACM SIGPLAN International Symposium on Memory Management (ISMM 2023)
Preview abstract
Memory allocators and runtime systems can leverage dynamic properties of heap allocations – such as object lifetimes, hotness or access correlations – to improve performance and resource consumption. A significant amount of work has focused on approaches that collect this information in performance profiles and then use it in new memory allocator or runtime designs, both offline (in ahead-of-time compilers) and online (in JIT compilers). This is a special instance of profile-guided optimization.
This approach has significant disadvantages: 1) The profiling oftentimes introduces substantial overheads, which are prohibitive in many production scenarios, 2) Creating a representative profiling run adds significant engineering complexity and reduces deployment velocity, and 3) Profiles gathered ahead of time or during the warm-up phase of a server are often not representative of all workload behavior and may miss important corner cases.
In this paper, we investigate a fundamentally different approach. Instead of deriving heap allocation properties from profiles, we explore the ability of neural network models to predict them from the statically available code. As an intellectual abstract, we do not offer a conclusive answer but describe the trade-off space of this approach, investigate promising directions, motivate these directions with data analysis and experiments, and highlight challenges that future work needs to overcome.
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Learning to Answer Semantic Queries over Code
Surya Prakash Sahu
Madhurima Mandal
Shikhar Bharadwaj
Aditya Kanade
Shirish Shevade
Google Research(2022)
Preview abstract
During software development, developers need answers to queries about semantic
aspects of code. Even though extractive question-answering using neural approaches has been studied widely in natural languages, the problem of answering
semantic queries over code using neural networks has not yet been explored. This
is mainly because there is no existing dataset with extractive question and answer pairs over code involving complex concepts and long chains of reasoning.
We bridge this gap by building a new, curated dataset called CodeQueries, and
proposing a neural question-answering methodology over code.
We build upon state-of-the-art pre-trained models of code to predict answer and
supporting-fact spans. Given a query and code, only some of the code may be
relevant to answer the query. We first experiment under an ideal setting where
only the relevant code is given to the model and show that our models do well. We
then experiment under three pragmatic considerations: (1) scaling to large-size
code, (2) learning from a limited number of examples and (3) robustness to minor
syntax errors in code. Our results show that while a neural model can be resilient
to minor syntax errors in code, increasing size of code, presence of code that is not
relevant to the query, and reduced number of training examples limit the model
performance. We are releasing our data and models
to facilitate future work on
the proposed problem of answering semantic queries over code.
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Graph Representations of Python Programs via Source-level Static Analysis
Vincent Josua Hellendoorn
Arxiv(2022)
Preview abstract
Graph representations of programs are commonly a central element of machine learning for code research. We introduce an open source Python library python_graphs that applies static analysis to construct graph representations of Python programs suitable for training machine learning models. Our library admits the construction of control-flow graphs, data-flow graphs, and composite "program graphs" that combine control-flow, data-flow, syntactic, and lexical information about a program. We present the capabilities and limitations of the library, perform a case-study applying the library to millions of competitive programming submissions, and showcase the library's utility for machine learning research.
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Preview abstract
Designing a suitable representation for code-reasoning tasks is challenging in
aspects such as the kinds of program information to model, how to combine them,
and how much context to consider. We propose CodeTrek, a deep learning approach
that addresses these challenges by representing codebases as databases that conform
to rich relational schemas. The relational representation not only allows CodeTrek
to uniformly represent diverse kinds of program information, but also to leverage
program-analysis queries to derive new semantic relations, which can be readily
incorporated without further architectural engineering. CodeTrek embeds this
relational representation using a set of walks that can traverse different relations
in an unconstrained fashion, and incorporates all relevant attributes along the way.
We evaluate CodeTrek on four diverse and challenging Python tasks: variable
misuse, exception prediction, unused definition, and variable shadowing. CodeTrek
achieves an accuracy of 91%, 63%, 98%, and 94% on these tasks respectively, and
outperforms state-of-the-art neural models by 2--19% points.
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Learning to Walk over Relational Graphs of Source Code
Pardis Pashakhanloo
Aaditya Naik
Hanjun Dai
Mayur Naik
Deep Learning for Code (DL4C) Workshop @ ICLR 2022(2022)
Preview abstract
Information-rich relational graphs have shown great potential in designing effective representations of code for program-understanding tasks. However, the
wealth of structural and semantic information in such graphs can overwhelm models, because of their limited input size. A promising approach for overcoming this
challenge is to gather presumed-relevant but smaller context from a larger graph,
and random walks over graphs was one of the first such approaches discovered.
We propose a deep-learning approach that improves upon random walks by learning task-specific walk policies that guide the traversal of the graph towards the
most relevant context. In the setting of relational graphs representing programs
and their semantic properties, we observe that models that employ learned policies for guiding walks are 6--36% points more accurate than models that employ
uniform random walks, and 0.2--3.5% points more accurate than models that employ expert knowledge for guiding the walks.
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Snowboard: Finding Kernel Concurrency Bugs through Systematic Inter-thread Communication Analysis
Sishuai Gong
Pedro Fonseca
Proceedings of the 28th ACM Symposium on Operating Systems Principles(2021) (to appear)
Preview abstract
Kernel concurrency bugs are challenging to find because they depend on very specific thread interleavings and test inputs. While separately exploring kernel thread interleavings or test inputs has been closely examined, jointly exploring interleavings and test inputs has received little attention, in part due to the resulting vast search space. Using precious, limited testing resources to explore this search space and execute just the right concurrent tests in the proper order is critical.
This paper proposes Snowboard a testing framework that generates and executes concurrent tests by intelligently exploring thread interleavings and test inputs jointly. The design of Snowboard is based on a concept called potential memory communication (PMC), a guess about pairs of tests that, when executed concurrently, are likely to perform memory accesses to shared addresses, which in turn may trigger concurrency bugs. To identify PMCs, Snowboard runs tests sequentially from a fixed initial kernel state, collecting their memory accesses. It then pairs up tests that write and read the same region into candidate concurrent tests. It executes those tests using the associated PMC as a scheduling hint to focus interleaving search only on those schedules that directly affect the relevant memory accesses. By clustering candidate tests on various features of their PMCs, Snowboard avoids testing similar behaviors, which would be inefficient. Finally, by executing tests from small clusters first, it prioritizes uncommon suspicious behaviors that may have received less scrutiny.
Snowboard discovered 14 new concurrency bugs in Linux kernels 5.3.10 and 5.12-rc3, of which 12 have been confirmed by developers. Six of these bugs cause kernel panics and filesystem errors, and at least two have existed in the kernel for many years, showing that this approach can uncover hard-to-find, critical bugs. Furthermore, we show that covering as many distinct pairs of uncommon read/write instructions as possible is the test-prioritization strategy with the highest bug yield for a given test-time budget.
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SpreadsheetCoder: Formula Prediction from Semi-structured Context
Xinyun Chen
Rishabh Singh
Hanjun Dai
Max Lin
Proceedings of the 38th International Conference on Machine Learning (ICML)(2021)
Preview abstract
Spreadsheet formula prediction has been an important
program synthesis problem with many
real-world applications. Previous works typically
utilize input-output examples as the specification
for spreadsheet formula synthesis, where each
input-output pair simulates a separate row in the
spreadsheet. However, this formulation does not
fully capture the rich context in real-world spreadsheets.
First, spreadsheet data entries are organized
as tables, thus rows and columns are not necessarily
independent from each other. In addition,
many spreadsheet tables include headers, which
provide high-level descriptions of the cell data.
However, previous synthesis approaches do not
consider headers as part of the specification. In
this work, we present the first approach for synthesizing
spreadsheet formulas from tabular context,
which includes both headers and semi-structured
tabular data. In particular, we propose SpreadsheetCoder,
a BERT-based model architecture
to represent the tabular context in both row-based
and column-based formats. We train our model on
a large dataset of spreadsheets, and demonstrate
that SpreadsheetCoder achieves top-1 prediction
accuracy of 42:51%, which is a considerable
improvement over baselines that do not employ
rich tabular context. Compared to a rule-based
system, SpreadsheetCoder assists 82% more
users in composing formulas on Google Sheets.
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