Parallelizing Flow-Sensitive Demand-Driven Points-to Analysis

Inclusion-based set constraint solving is the most popular technique for whole-program points-to analysis whereby an analysis is typically formulated as repeatedly resolving constraints between points-to sets of program variables. The set union operation is central to this process. The number of points-to sets can grow as analyses become more precise and input programs become larger, resulting in more time spent performing unions and more space used storing these points-to sets. Most existing approaches focus on improving scalability of precise points-to analyses from an algorithmic perspective and there has been less research into improving the data structures behind the analyses. Bit-vectors as one of the more popular data structures have been used in several mainstream analysis frameworks to represent points-to sets. To store memory objects in bit-vectors, objects need to mapped to integral identifiers. We observe that this object-to-identifier mapping is critical for a compact points-to set representation and the set union operation. If objects in the same points-to sets (co-pointees) are not given numerically close identifiers, points-to resolution can cost significantly more space and time. Without data on the unpredictable points-to relations which would be discovered by the analysis, an ideal mapping is extremely challenging. In this paper, we present a new approach to inclusion-based analysis by compacting points-to sets through object clustering. Inspired by recent staged analysis where an auxiliary analysis produces results approximating a more precise main analysis, we formulate points-to set compaction as an optimisation problem solved by integer programming using constraints generated from the auxiliary analysis’s results in order to produce an effective mapping. We then develop a more approximate mapping, yet much more efficiently, using hierarchical clustering to compact bit-vectors. We also develop an improved representation of bit-vectors (called core bit-vectors) to fully take advantage of the newly produced mapping. Our approach requires no algorithmic change to the points-to analysis. We evaluate our object clustering on flow sensitive points-to analysis using 8 open-source programs (>3.1 million lines of LLVM instructions) and our results show that our approach can successfully improve the analysis with an up to 1.83× speed up and an up to 4.05× reduction in memory usage.

Probabilistic points-to analysis is an analysis technique for defining the probabilities on the points-to relations in programs. It provides the compiler with some optimization chances such as speculative dead store elimination, speculative redundancy elimination, and speculative code scheduling. Although several static probabilistic points-to analysis techniques have been developed for C language, they cannot be applied directly to Java because they do not handle the classes, objects, inheritances and invocations of virtual methods. In this paper, we propose a context-insensitive and flow-sensitive probabilistic points-to analysis for Java (JPPA) for statically predicting the probability of points-to relations at all program points (i.e., points before or after statements) of a Java program. JPPA first constructs an interprocedural control flow graph (ICFG) for a Java program, whose edges are labeled with the probabilities calculated by an algorithm based on a static branch prediction approach, and then calculates the probabilistic points-to relations of the program based upon the ICFG. We have also developed a tool called Lukewarm to support JPPA and conducted an experiment to compare JPPA with a traditional context-insensitive and flow-sensitive points-to analysis approach. The experimental results show that JPPA is a precise and effective probabilistic points-to analysis technique for Java.Keywordspoints-to analysisprobabilityJava

Points-to analysis is a static program analysis aiming at analyzing the reference structure of dynamically allocated objects at compile-time. It constitutes the basis for many analyses and optimizations in software engineering and compiler construction. Sparse program representations, such as Whole Program Points-to Graph (WPP2G) and Points-to SSA (P2SSA), represent only dataflow that is directly relevant for points-to analysis. They have proved to be practical in terms of analysis precision and efficiency. However, intra-procedural control flow information is removed from these representations, which sacrifices analysis precision to improve analysis performance. We show an approach for keeping control flow related information even in sparse program representations by representing control flow effects as operations on the data transferred, i.e., as dataflow information. These operations affect distinct paths of the program differently, thus yielding a certain degree of path-sensitivity. Our approach works with both WPP2G and P2SSA representations. We apply the approach to P2SSA-based and flow-sensitive points-to analysis and evaluate a context-insensitive and a context-sensitive variant. We assess our approach using abstract precision metrics. Moreover, we investigate the precision improvements and performance penalties when used as an input to three source-code-level analyses: dead code, cast safety, and null pointer analysis.

Developing scalable and precise points-to analyses is increasingly important for analysing and optimising object-oriented programs where pointers are used pervasively. An incremental analysis for a program updates the existing analysis information after program changes to avoid reanalysing it from scratch. This can be efficiently deployed in software development environments where code changes are often small and frequent. This paper presents an incremental approach for demand-driven context-sensitive points-to analyses based on Context-Free Language (CFL) reachability. By tracing the CFL-reachable paths traversed in computing points-to sets, we can precisely identify and recompute on demand only the points-to sets affected by the program changes made. Combined with a flexible policy for controlling the granularity of traces, our analysis achieves significant speedups with little space overhead over reanalysis from scratch when evaluated with a null dereferencing client using 14 Java benchmarks.

Many program analyses benefit, both in precision and performance, from precise pointer analysis. An important dimension of pointer analysis precision is flow-sensitivity, which has been shown to be useful for applications such as program verification and static analysis of binary code, among many others. However, flow-sensitive pointer analysis has historically been unable to scale to programs with millions of lines of code. We present a new flow-sensitive pointer analysis algorithm that is an order of magnitude faster than the existing state of the art, enabling for the first time flow-sensitive pointer analysis for programs with millions of lines of code. Our flow-sensitive algorithm is based on a sparse representation of program code created by a staged, flow-insensitive pointer analysis. We explain how this new algorithm is a member of a new family of pointer analysis algorithms that deserves further study.

By respecting program control-flow, flow-sensitive pointer analysis promises more precise results than its flow-insensitive counterpart. However, existing heap abstractions for C and C++ flow-sensitive pointer analyses model the heap by creating a single abstract heap object for each memory allocation. Two runtime heap objects which originate from the same allocation site are imprecisely modelled using one abstract object, which makes them share the same imprecise points-to sets and thus reduces the benefit of analysing heap objects flow-sensitively. On the other hand, equipping flow-sensitive analysis with context-sensitivity, whereby an abstract heap object would be created (cloned) per calling context, can yield a more precise heap model, but at the cost of uncontrollable analysis overhead when analysing larger programs. This paper presents TypeClone, a new type-based heap model for flow-sensitive analysis. Our key insight is to differentiate concrete heap objects lazily using type information at use sites within the program control-flow (e.g., when accessed via pointer dereferencing) for programs which conform to the strict aliasing rules set out by the C and C++ standards. The novelty of TypeClone lies in its lazy heap cloning: an untyped abstract heap object created at an allocation site is killed and replaced with a new object (i.e. a clone), uniquely identified by the type information at its use site, for flow-sensitive points-to propagation. Thus, heap cloning can be performed within a flow-sensitive analysis without the need for context-sensitivity. Moreover, TypeClone supports new kinds of strong updates for flow-sensitive analysis where heap objects are filtered out from imprecise points-to relations at object use sites according to the strict aliasing rules. Our method is neither strictly superior nor inferior to context-sensitive heap cloning, but rather, represents a new dimension that achieves a sweet spot between precision and efficiency. We evaluate our analysis by comparing TypeClone with state-of-the-art sparse flow-sensitive points-to analysis using the 12 largest programs in GNU Coreutils. Our experimental results also confirm that TypeClone is more precise than flow-sensitive pointer analysis and is able to, on average, answer over 15% more alias queries with a no-alias result.

Doing a flow-sensitive points-to analysis benefits many program analyses which need precise results, however, many prefer to do a flow-insensitive analysis to gain speed and overcome the memory limitations of a flow-sensitive points-to analysis. We are able to overcome these limitations by representing and manipulating points-to sets more efficiently. Binary Decision Diagrams (BDDs) have been shown to be a very efficient representation of points-to sets. A reasonable formulation of the solution is of great importance to achieve this efficiency. In this work, we formulate and employ BDDs to represent points-to sets in flow-sensitive points-to analysis for Java programs. Our method was compared with default points-to set in Soot program analysis framework (hybrid points-to set). The results are very promising and show the effectiveness of our method for sufficiently large programs.

Object sensitivity is widely used as a context abstraction for computing the points-to information context-sensitively for object-oriented programming languages such as Java. Due to the combinatorial explosion of contexts in large object-oriented programs, k -object-sensitive pointer analysis (under k -limiting), denoted k -obj , is often inefficient even when it is scalable for small values of k , where k ⩽ 2 holds typically. A recent popular approach for accelerating k -obj trades precision for efficiency by instructing k -obj to analyze only some methods in a program context-sensitively, determined heuristically by a pre-analysis. In this article, we investigate how to develop a fundamentally different approach, Eagle , for designing a pre-analysis that can make k -obj run significantly faster while maintaining its precision. The novelty of Eagle is to enable k -obj to analyze a method with partial context sensitivity (i.e., context-sensitively for only some of its selected variables/allocation sites) by solving a context-free-language (CFL) reachability problem based on a new CFL-reachability formulation of k -obj . By regularizing one CFL for specifying field accesses and using another CFL for specifying method calls, we have formulated Eagle as a fully context-sensitive taint analysis (without k -limiting) that is both effective (by selecting the variables/allocation sites to be analyzed by k -obj context-insensitively so as to reduce the number of context-sensitive facts inferred by k -obj in the program) and efficient (by running linearly in terms of the number of pointer assignment edges in the program). As Eagle represents the first precision-preserving pre-analysis, our evaluation focuses on demonstrating its significant performance benefits in accelerating k -obj for a set of popular Java benchmarks and applications, with call graph construction, may-fail-casting, and polymorphic call detection as three important client analyses.

We present a practical and scalable method for flow- and context-sensitive (FSCS) pointer analysis for C programs. Our method analyzes the pointers in a program level by level in terms of their points-to levels, allowing the points-to relations of the pointers at a particular level to be discovered based on the points-to relations of the pointers at this level and higher levels. This level-by-level strategy can enhance the scalability of the FSCS pointer analysis in two fundamental ways, by enabling (1) fast and accurate flow-sensitive analysis on full sparse SSA form using a flow-insensitive algorithm and (2) fast and accurate context-sensitive analysis using a full transfer function and a meet function for each procedure.

An Ahead-of-time Yet Context-Sensitive Points-to Analysis for Java

Database-backed applications form the backbone of modern software, yet their complexity poses significant challenges for static analysis. These applications involve intricate interactions among application code, diverse database frameworks such as JDBC, Hibernate, and Spring Data JPA, and languages like Java and SQL. In this paper, we introduce DBridge, the first pointer analysis specifically designed for Java database-backed applications, capable of statically constructing comprehensive Java-to-database value flows. DBridge unifies application code analysis, database access specification modeling, SQL analysis, and database abstraction within a single pointer analysis framework, capturing interactions across a wide range of database access APIs and frameworks. Additionally, we present DB-Micro, a new micro-benchmark suite with 824 test cases crafted to systematically evaluate static analysis for database-backed applications. Experiments on DB-Micro and large, complex, real-world applications demonstrate DBridge's effectiveness, achieving high recall and precision in building Java-to-database value flows efficiently and outperforming state-of-the-art tools in SQL statement identification. To further validate DBridge's utility, we develop three client analyses for security and program understanding. Evaluation on these real-world applications reveals 30 Stored XSS attack vulnerabilities and 3 horizontal broken access control vulnerabilities, all previously undiscovered and real, as well as a high detection rate in impact analysis for schema changes. By open-sourcing DBridge (14K LoC) and DB-Micro (22K LoC), we seek to help advance static analysis for modern database-backed applications in the future.

Many graph analysis problems can be formulated as formal language-constrained path querying problems where the formal languages are used as constraints for navigational path queries. Recently, the context-free language (CFL) reachability formulation has become very popular and can be used in many areas, for example, querying graph databases, Resource Description Framework (RDF) analysis. However, the generative capacity of context-free grammars (CFGs) is too weak to generate some complex queries, for example, from natural languages, and the various extensions of CFGs have been proposed. Multiple context-free grammar (MCFG) is one of such extensions of CFGs. Despite the fact that, to the best of our knowledge, there is no algorithm for MCFL-reachability, this problem is known to be decidable. This paper is devoted to developing the first such algorithm for the MCFL-reachability problem. The essence of the proposed algorithm is to use a set of Boolean matrices and operations on them to find paths in a graph that satisfy the given constraints. The main operation here is Boolean matrix multiplication. As a result, the algorithm returns a set of matrices containing all information needed to solve the MCFL-reachability problem. The presented algorithm is implemented in Python using GraphBLAS API. An analysis of real RDF data and synthetic graphs for some MCFLs is performed. The study showed that using a sparse format for matrix storage and parallel computing for graphs with tens of thousands of edges the analysis time can be 10–20 minutes. The result of the analysis provides tens of millions of reachable vertex pairs. The proposed algorithm can be applied in problems of static code analysis, bioinformatics, network analysis, as well as in graph databases when a path query cannot be expressed using context-free grammars. The provided algorithm is linear algebra-based, hence, it allows one to use high-performance libraries and utilize modern parallel hardware.

We introduce a new region-based SELective Flow-Sensitive (Selfs) approach to inter-procedural pointer analysis for C that operates on the regions partitioned from a program. Flow-sensitivity is maintained between the regions but not inside, making traditional flow-insensitive and flow-sensitive as well as recent sparse flow-sensitive analyses all special instances of our Selfs framework. By separating region partitioning as an independent concern from the rest of the pointer analysis, Selfs facilitates the development of flow-sensitive variations with desired efficiency and precision tradeoffs by reusing existing pointer resolution algorithms. We also introduce a new unification-based approach for region partitioning to demonstrate the generality and flexibility of our Selfs framework, as evaluated using SPEC2000/2006 benchmarks in LLVM.

Programs which manipulate pointers are hard to debug. Pointer analysis algorithms (originally aimed at optimizing compilers) may provide some remedy by identifying potential errors such as dereferencing NULL pointers by statically analyzing the behavior of programs on all their input data.Our goal is to identify the "core program analysis techniques" that can be used when developing realistic tools which detect memory errors at compile time without, generating too many false alarms. Our preliminary experience indicates that the following techniques are necessary: (i) finding aliases between pointers, (ii) flow sensitive techniques that account, for the program control flow constructs. (iii) partial interpretation of conditional statements, (iv) analysis of the relationships between pointers, and sometimes (v) analysis of the underlying data structures manipulated by the C program.We show that a combination of these techniques can yield better results than those achieved by state of the art tools. Yet it is not clear to us whether our ideas are applicable to large programs.

Communicating Reactive Processes (CRP) paradigm unifies asynchronous and synchronous mechanisms of concurrent programming languages. As an example, CRP unifies Esterel and Hoare's Communicating Sequential Processes (CSP). It has been earlier shown that such a unification and in particular CRP can be used for the specification of hybrid systems and dynamic real-time systems. In this paper, we extend the CRP to support hierarchical refinement and describe a compositional semantics. Further, we show how verification can be done using the verification techniques and tools used for the verification of Esterel programs. We illustrate how a careful separation of Esterel and CSP mechanisms in CRP has enabled the use of the technique of verification by reductions for verification and illustrate the use of tools such as Auto/Autograph for the verification of CRP programs through the banker-teller example.