DOCSLIB.ORG

Tailoring Programs for Static Analysis Via Program Transformation

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Tailoring Programs for Static Analysis Via Program Transformation Tailoring Programs for Static Analysis via Program Transformation Rijnard van Tonder Claire Le Goues School of Computer Science School of Computer Science Carnegie Mellon University Carnegie Mellon University USA USA [email protected] [email protected] ABSTRACT analyses in practice. Analyses must approximate, both theoreti- Static analysis is a proven technique for catching bugs during soft- cally [22, 25] and in the interest of practicality [9, 11]. Developers ware development. However, analysis tooling must approximate, are sensitive to whether tools integrate seamlessly into their exist- both theoretically and in the interest of practicality. False positives ing workflows [21]; at minimum analyses must be fast, surface few are a pervading manifestation of such approximations—tool con- false positives, and provide mechanisms to suppress warnings [10]. figuration and customization is therefore crucial for usability and The problem is that the choices that tools make toward these ends directing analysis behavior. To suppress false positives, develop- are broadly generic, and the divergence between tool assumptions ers readily disable bug checks or insert comments that suppress and program reality (i.e., language features or quality concerns) spurious bug reports. Existing work shows that these mechanisms can lead to unhelpful, overwhelming, or incorrect output [20]. fall short of developer needs and present a significant pain point Tool configuration and customization is crucial for usability and for using or adopting analyses. We draw on the insight that an directing analysis behavior. The inability to easily and selectively analysis user always has one notable ability to influence analysis disable analysis checks and suppress warnings presents a significant behavior regardless of analyzer options and implementation: modi- pain point for analysis users [10]. Common existing mechanisms fying their program. We present a new technique for automated, include analysis options for turning off entire bug classes (gen- generic, and temporary code changes that tailor to suppress spuri- erally too coarse [21]) or adding comment-like annotations that ous analysis errors. We adopt a rule-based approach where simple, suppress spurious warnings at particular lines (a predominantly declarative templates describe general syntactic changes for code manual exercise that leads to code smells and is insufficiently gran- patterns that are known to be problematic for the analyzer. Our ular [10, 21]). It is notably the analysis author, not the user, who has technique promotes program transformation as a general primitive agency over the shape of these analysis knobs: which configuration for improving the fidelity of analysis reports (we treat any given options are available and how to suppress errors. It follows that it analyzer as a black box). We evaluate using five different static is infeasible for analysis writers to foresee and accommodate indi- analyzers supporting three different languages (C, Java, and PHP) vidual user preferences or analysis corner cases through a myriad on large, real world programs (up to 800KLOC). We show that our of configuration options or suppression mechanisms. approach is effective in sidestepping long-standing and complex An analysis user always has one notable ability to influence anal- issues in analysis implementations. ysis behavior and output: modifying their program. For example, developers may slightly modify existing code in a way that sup- ACM Reference Format: presses false positives or undesired warnings. A concrete example Rijnard van Tonder and Claire Le Goues. 2020. Tailoring Programs for Static 1 Analysis via Program Transformation. In 42nd International Conference on is the following change, which was made in rsyslog to suppress a Software Engineering (ICSE ’20), May 23–29, 2020, Seoul, Republic of Korea. Clang Static Analyzer warning: ACM, New York, NY, USA, 11 pages. https://doi.org/10.1145/3377811.3380343 - if(strcmp(rectype, "END")) { £+ // clang static analyzer work-around 1 INTRODUCTION + const char *const const_END = "END"; Writing and maintaining high-quality, bug-free software remains a + if(strcmp(rectype, const_END)) { largely manual and expensive process. Static analysis has proven indispensable in software quality assurance for automatically catch- The analyzer¢ warns that a potential out-of-bounds access¡ occurs ing bugs early in the development process [31]. A number of open when comparing two strings using strcmp. However, the warning challenges underlie successful adoption and integration of static only surfaces when complex macro expansions take place (in this case, macro expansion activates for strcmp because the second ar- Permission to make digital or hard copies of all or part of this work for personal or gument is a string literal). One contributor notes that under normal classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation circumstances these warnings are suppressed for macros, but can on the first page. Copyrights for components of this work owned by others than the surface if macro preprocessing is done manually.2 The workaround author(s) must be honored. Abstracting with credit is permitted. To copy otherwise, or in this case extracts the string literal out of the strcmp call so that republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from [email protected]. no macro expansion takes place. After the change, the analyzer ICSE ’20, May 23–29, 2020, Seoul, Republic of Korea sees strcmp as a C library function and no longer emits a warning. © 2020 Copyright held by the owner/author(s). Publication rights licensed to ACM. ACM ISBN 978-1-4503-7121-6/20/05...$15.00 1https://github.com/rsyslog/rsyslog/commit/ea7497 https://doi.org/10.1145/3377811.3380343 2https://bugs.llvm.org/show_bug.cgi?id=20144 ICSE ’20, May 23–29, 2020, Seoul, Republic of Korea Rijnard van Tonder and Claire Le Goues In practice, modifying programs to avoid analyzer issues are exer- 1 function test(): void{ cised as manual, one-off changes. Changes like the one above can 2 § if (($file= @fopen( 'file ', 'wb+ ')) === false){ ¤ 3 return ; have the undesirable side-effect of persisting in the code solely to 4} suppress unwanted analysis warnings. Despite these shortcomings, 5 modification of the analysis target (the program) does, however, al- 6// analyzer complains that $file may be false 7 if (\fputcsv($file, [1,2,3]) === false){ low a primitive for analysis users to draw on their particular domain 8\fclose($file); knowledge of their code to positively influence analysis behavior. 9 return ; 10} For example, a developer may recognize that a particular API call 11... is the cause of a false positive resource leak and modify or model 12\fclose($file); the call differently to suppress a false positive.3 Our technique in 13} particular affords agency to analysis users to change and suppress analysis behavior when no recourse is available in tool support (e.g., (a) Assigning¦ the result of fopen to $file in Line 2 confuses the ana-¥ when analysis maintainers delay fixing analysis issues, or limit tool lyzer. It doesn’t track the effect that $file is not false on Line 7, and configuration options). Our insight is that the same flavor ofone- emits a false positive warning that $file may be false when passed to $putcsv. off, manual code changes like the one above can apply generally and automatically to remedy analysis shortcomings. Additionally, 1 function test(): void{ 2 § $file= @fopen( 'file ', 'wb+ '); ¤ workaround changes need not have the undesirable trait of per- 3 if ($file === false){ sisting in production code, and are applied only temporarily while 4 return ; performing analysis. 5} 6... We propose a rule-based approach where simple, declarative 7} templates describe general syntactic changes for known problem- atic code patterns. Undesired warnings and false positives are thus (b) An¦ analysis user proposed this workaround: extract the assign-¥ removed during analysis by rewriting code fragments. Our ap- ment out of the conditional. This allows the analyzer to correctly proach can be seen as a preprocessing step that tailors programs track the assignment effect and does not emit a false positive. Unfor- for analysis using lightweight syntactic changes. It operates on tunately this approach is hard to blanket-apply automatically and the basis of temporary suppression (a desirable trait in configuring diverges from developer preferences who prefer the former style analyses [21]) and also enables catching false positives before they for readability. happen by rewriting problematic patterns. Since patterns can occur across projects, codifying transformations as reusable templates Figure 2: Variable assignment inside if-statements can cause amortizes developer effort for suppressing false positives. a false positive report in PHPStan. A workaround is to put the The notion that syntactic transformations abstract semantic assignment outside of the if conditional. transformations [13] underpins our intuition that manipulating syntax can achieve desirable changes in the analysis domain and implementation. Work on semantic properties of transformations • We show that our approach is effective in improving existing emphasize the potential for improving analysis precision [26, 28], static analyses and resolves
Load more

Recommended publications
  • Source-To-Source Translation and Software Engineering
    Journal of Software Engineering and Applications, 2013, 6, 30-40 http://dx.doi.org/10.4236/jsea.2013.64A005 Published Online April 2013 (http://www.scirp.org/journal/jsea) Source-to-Source Translation and Software Engineering David A. Plaisted Department of Computer Science, University of North Carolina at Chapel Hill, Chapel Hill, USA. Email: [email protected] Received February 5th, 2013; revised March 7th, 2013; accepted March 15th, 2013 Copyright © 2013 David A. Plaisted. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT Source-to-source translation of programs from one high level language to another has been shown to be an effective aid to programming in many cases. By the use of this approach, it is sometimes possible to produce software more cheaply and reliably. However, the full potential of this technique has not yet been realized. It is proposed to make source- to-source translation more effective by the use of abstract languages, which are imperative languages with a simple syntax and semantics that facilitate their translation into many different languages. By the use of such abstract lan- guages and by translating only often-used fragments of programs rather than whole programs, the need to avoid writing the same program or algorithm over and over again in different languages can be reduced. It is further proposed that programmers be encouraged to write often-used algorithms and program fragments in such abstract languages. Libraries of such abstract programs and program fragments can then be constructed, and programmers can be encouraged to make use of such libraries by translating their abstract programs into application languages and adding code to join things together when coding in various application languages.
    [Show full text]
  • APPLICATION of the DELTA DEBUGGING ALGORITHM to FINE-GRAINED AUTOMATED LOCALIZATION of REGRESSION FAULTS in JAVA PROGRAMS Master’S Thesis
    TALLINN UNIVERSITY OF TECHNOLOGY Faculty of Information Technology Marina Nekrassova 153070IAPM APPLICATION OF THE DELTA DEBUGGING ALGORITHM TO FINE-GRAINED AUTOMATED LOCALIZATION OF REGRESSION FAULTS IN JAVA PROGRAMS Master’s thesis Supervisor: Juhan Ernits PhD Tallinn 2018 TALLINNA TEHNIKAÜLIKOOL Infotehnoloogia teaduskond Marina Nekrassova 153070IAPM AUTOMATISEETITUD SILUMISE RAKENDAMINE VIGADE LOKALISEERIMISEKS JAVA RAKENDUSTES Magistritöö Juhendaja: Juhan Ernits PhD Tallinn 2018 Author’s declaration of originality I hereby certify that I am the sole author of this thesis. All the used materials, references to the literature and the work of others have been referred to. This thesis has not been presented for examination anywhere else. Author: Marina Nekrassova 08.01.2018 3 Abstract In software development, occasionally, in the course of software evolution, the functionality that previously worked as expected stops working. Such situation is typically denoted by the term regression. To detect regression faults as promptly as possible, many agile development teams rely nowadays on automated test suites and the practice of continuous integration (CI). Shortly after the faulty change is committed to the shared mainline, the CI build fails indicating the fact of code degradation. Once the regression fault is discovered, it needs to be localized and fixed in a timely manner. Fault localization remains mostly a manual process, but there have been attempts to automate it. One well-known technique for this purpose is delta debugging algorithm. It accepts as input a set of all changes between two program versions and a regression test that captures the fault, and outputs a minimized set containing only those changes that directly contribute to the fault (in other words, are failure-inducing).
    [Show full text]
  • Repairnator Patches Programs Automatically
    Repairnator patches programs automatically Ubiquity Volume 2019, Number July (2019), Pages 1-12 Martin Monperrus, Simon Urli, Thomas Durieux, Matias Martinez, Benoit Baudry, Lionel Seinturier DOI: 10.1145/3349589 Repairnator is a bot. It constantly monitors software bugs discovered during continuous integration of open-source software and tries to fix them automatically. If it succeeds in synthesizing a valid patch, Repairnator proposes the patch to the human developers, disguised under a fake human identity. To date, Repairnator has been able to produce patches that were accepted by the human developers and permanently merged into the code base. This is a milestone for human-competitiveness in software engineering research on automatic program repair. Programmers have always been unhappy that mistakes are so easy, and they need to devote much of their work to finding and repairing defects. Consequently, there has been considerable research on detecting bugs, preventing bugs, or even proving their absence under specific assumptions. Yet, regardless of how bugs are found, this vast research has assumed that a human developer would fix the bugs. A decade ago, a group of researchers took an alternative path: regardless of how a bug is detected, they envisioned that an algorithm would analyze it to synthesize a patch. The corresponding research field is called "automated program repair." This paradigm shift has triggered a research thrust with significant achievements [1]: Some past bugs in software repositories would have been amenable to automatic correction. In this following example, a patch fixes an if- statement with incorrect condition (a patch inserts, deletes, or modifies source code): - if (x < 10) + if (x ≤ 10) foo(); Armed with the novel mindset of repairing instead of detecting, and with opulent and cheap computing power, it is possible today to automatically explore large search spaces of possible patches.
    [Show full text]
  • Extending Fortran with Meta-Programming
    OpenFortran: Extending Fortran with Meta-programming Songqing Yue and Jeff Gray Department of Computer Science University of Alabama Tuscaloosa, AL, USA {syue, gray}@cs.ua.edu Abstract—Meta-programming has shown much promise for manipulated [1]. MOPs add the ability of meta-programming improving the quality of software by offering programming to programming languages by providing users with standard language techniques to address issues of modularity, reusability, interfaces to modify the internal implementation of the maintainability, and extensibility. A system that supports meta- program. Through the interface, programmers can programming is able to generate or manipulate other programs incrementally change the implementation and the behavior of a to extend their behavior. This paper describes OpenFortran, a program to better suit their needs. Furthermore, a metaprogram Meta-Object Protocol (MOP) that is able to bring the power of can capture the needs of a commonly needed feature and be meta-programming to Fortran, one of the most widely used applied to several different base programs. languages in the area of High Performance Computing (HPC). OpenFortran provides a framework that allows library A MOP may perform the underling adaptation of the base developers to build arbitrary source-to-source program program at either run-time or compile-time. Run-time MOPs transformation libraries for Fortran programs. To relieve the function while a program is executing and can be used to burden of learning the details about how the underlying perform real-time adaptation, for example the Common Lisp transformations are performed, a domain-specific language Object System (CLOS) [13] that allows the mechanisms of named SPOT has been created that allows developers to specify inheritance, method dispatching, and class instantiation to be direct manipulation of programs.
    [Show full text]
  • ROSE Tutorial: a Tool for Building Source-To-Source Translators Draft Tutorial (Version 0.9.11.115)
    ROSE Tutorial: A Tool for Building Source-to-Source Translators Draft Tutorial (version 0.9.11.115) Daniel Quinlan, Markus Schordan, Richard Vuduc, Qing Yi Thomas Panas, Chunhua Liao, and Jeremiah J. Willcock Lawrence Livermore National Laboratory Livermore, CA 94550 925-423-2668 (office) 925-422-6278 (fax) fdquinlan,panas2,[email protected] [email protected] [email protected] [email protected] [email protected] Project Web Page: www.rosecompiler.org UCRL Number for ROSE User Manual: UCRL-SM-210137-DRAFT UCRL Number for ROSE Tutorial: UCRL-SM-210032-DRAFT UCRL Number for ROSE Source Code: UCRL-CODE-155962 ROSE User Manual (pdf) ROSE Tutorial (pdf) ROSE HTML Reference (html only) September 12, 2019 ii September 12, 2019 Contents 1 Introduction 1 1.1 What is ROSE.....................................1 1.2 Why you should be interested in ROSE.......................2 1.3 Problems that ROSE can address...........................2 1.4 Examples in this ROSE Tutorial...........................3 1.5 ROSE Documentation and Where To Find It.................... 10 1.6 Using the Tutorial................................... 11 1.7 Required Makefile for Tutorial Examples....................... 11 I Working with the ROSE AST 13 2 Identity Translator 15 3 Simple AST Graph Generator 19 4 AST Whole Graph Generator 23 5 Advanced AST Graph Generation 29 6 AST PDF Generator 31 7 Introduction to AST Traversals 35 7.1 Input For Example Traversals............................. 35 7.2 Traversals of the AST Structure............................ 36 7.2.1 Classic Object-Oriented Visitor Pattern for the AST............ 37 7.2.2 Simple Traversal (no attributes)....................... 37 7.2.3 Simple Pre- and Postorder Traversal....................
    [Show full text]
  • Towards Large-Scale Refactoring for Ocaml
    Towards Large-scale Refactoring for OCaml REUBEN N. S. ROWE, University of Kent, UK SIMON J. THOMPSON, University of Kent, UK Refactoring is the process of changing the way a program works without changing its overall behaviour. The functional programming paradigm presents its own unique challenges to refactoring. For the OCaml language in particular, the expressiveness of its module system makes this a highly non-trivial task. The use of PPX preprocessors, other language extensions, and idiosyncratic build systems complicates matters further. We begin to address the question of how to refactor large OCaml programs by looking at a particular refactoring—value binding renaming—and implementing a prototype tool to carry it out. Our tool, Rotor, is developed in OCaml itself and combines several features to manage the complexities of refactoring OCaml code. Firstly it defines a rich, hierarchical way of identifying bindings which distinguishes between structures and functors and their associated module types, and is able to refer directly to functor parameters. Secondly it makes use of the recently developed visitors library to perform generic traversals of abstract syntax trees. Lastly it implements a notion of ‘dependency’ between renamings, allowing refactorings to be computed in a modular fashion. We evaluate Rotor using a snapshot of Jane Street’s core library and its dependencies, comprising some 900 source files across 80 libraries, and a test suite of around 3000 renamings. We propose that the notion of dependency is a general one for refactoring, distinct from a refactoring ‘precondition’. Dependencies may actually be mutual, in that all must be applied together for each one individually to be correct, and serve as declarative specifications of refactorings.
    [Show full text]
  • Combining Source and Target Level Cost Analyses for Ocaml Programs
    Combining Source and Target Level Cost Analyses for OCaml Programs Stefan K. Muller Jan Hoffmann Carnegie Mellon University Carnegie Mellon University Abstract bounding gas usage in smart contracts [24]. More generally, Deriving resource bounds for programs is a well-studied it is an appealing idea to provide programmers with imme- problem in the programming languages community. For com- diate feedback about the efficiency of their code at design piled languages, there is a tradeoff in deciding when during time. compilation to perform such a resource analysis. Analyses at When designing a resource analysis for a compiled higher- the level of machine code can precisely bound the wall-clock level language, there is a tension between working on the execution time of programs, but often require manual anno- source code, the target code, or an intermediate represen- tations describing loop bounds and memory access patterns. tation. Advantages of analyzing the source code include Analyses that run on source code can more effectively derive more effective interaction with the programmer and more such information from types and other source-level features, opportunities for automation since the control flow and type but produce abstract bounds that do not directly reflect the information are readily available. The advantage of analyz- execution time of the compiled machine code. ing the target code is that analysis results apply to the code This paper proposes and compares different techniques for that is eventually executed. Many of the tools developed combining source-level and target-level resource analyses in in the programming languages community operate on the the context of the functional programming language OCaml.
    [Show full text]
  • A Bundle of Program Transformation Tools System Description
    ¡ ¢ £ ¤ ¦ ¨ ¨ ! $ % & ! % $ ' ( * * ( + - . / 0 XT: a bundle of program transformation tools system description Merijn de Jonge 1 CWI, Department SEN, PO Box 94079, 1090 GB Amsterdam, The Netherlands Eelco Visser 2 Universiteit Utrecht, Institute of Information and Computing Sciences PO Box 80089, 3508 TB Utrecht, The Netherlands Joost Visser 3 CWI, Department SEN, PO Box 94079, 1090 GB Amsterdam, The Netherlands Abstract XT bundles existing and newly developed program transformation libraries and tools into an open framework that supports component-based development of program transforma- tions. We discuss the roles of XT’s constituents in the development process of program transformation tools, as well as some experiences with building program transformation systems with XT. 1 Introduction Program transformation encompasses a variety of different, but related, language processing scenarios, such as optimization, compilation, normalization, and reno- vation. Across these scenarios, many common, or similar subtasks can be distin- guished, which opens possibilities for software reuse. To support and demonstrate such reuse across program transformation project boundaries, we have developed XT. XT is a bundle of existing and newly developed libraries and tools useful in the 4 Email:[email protected] 5 Email:[email protected] 6 Email:[email protected] 8 : : ; < > @ BC E G H J @ L N BE H P CH R T V CH Y V H [ ] _ ] 7 c 79 a b d f g i b j g a m oq q b s j g a m oq q b s context of program transformation. It bundles its constituents into an open frame- work for component-based transformation tool development, which is flexible and extendible.
    [Show full text]
  • When Polyhedral Transformations Meet SIMD Code Generation
    When Polyhedral Transformations Meet SIMD Code Generation Martin Kong Richard Veras Kevin Stock Ohio State University Carnegie Mellon University Ohio State University [email protected] [email protected] [email protected] Franz Franchetti Louis-Noel¨ Pouchet P. Sadayappan Carnegie Mellon University University of California Los Angeles Ohio State University [email protected] [email protected] [email protected] Abstract While hand tuned library kernels such as GotoBLAS address all Data locality and parallelism are critical optimization objectives for the above factors to achieve over 95% of machine peak for spe- performance on modern multi-core machines. Both coarse-grain par- cific computations, no vectorizing compiler today comes anywhere allelism (e.g., multi-core) and fine-grain parallelism (e.g., vector SIMD) close. Recent advances in polyhedral compiler optimization [5, 11] must be effectively exploited, but despite decades of progress at both have resulted in effective approaches to tiling for cache locality, ends, current compiler optimization schemes that attempt to address even for imperfectly nested loops. However, while significant per- data locality and both kinds of parallelism often fail at one of the three formance improvement over untiled code has been demonstrated, objectives. the absolute achieved performance is still very far from machine We address this problem by proposing a 3-step framework, which peak. A significant challenge arises from the fact that polyhedral aims for integrated data locality, multi-core parallelism and SIMD exe- cution of programs. We define the concept of vectorizable codelets, with compiler transformations to produce tiled code generally require properties tailored to achieve effective SIMD code generation for the auxiliary transformations like loop skewing, causing much more codelets.
    [Show full text]
  • Formalizing the SSA-Based Compiler for Verified Advanced Program Transformations Jianzhou Zhao University of Pennsylvania, [email protected]
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by ScholarlyCommons@Penn University of Pennsylvania ScholarlyCommons Publicly Accessible Penn Dissertations 1-1-2013 Formalizing the SSA-based Compiler for Verified Advanced Program Transformations Jianzhou Zhao University of Pennsylvania, [email protected] Follow this and additional works at: http://repository.upenn.edu/edissertations Part of the Computer Sciences Commons Recommended Citation Zhao, Jianzhou, "Formalizing the SSA-based Compiler for Verified Advanced Program Transformations" (2013). Publicly Accessible Penn Dissertations. 825. http://repository.upenn.edu/edissertations/825 This paper is posted at ScholarlyCommons. http://repository.upenn.edu/edissertations/825 For more information, please contact [email protected]. Formalizing the SSA-based Compiler for Verified Advanced Program Transformations Abstract Compilers are not always correct due to the complexity of language semantics and transformation algorithms, the trade-offs between compilation speed and verifiability,etc.The bugs of compilers can undermine the source-level verification efforts (such as type systems, static analysis, and formal proofs) and produce target programs with different meaning from source programs. Researchers have used mechanized proof tools to implement verified compilers that are guaranteed to preserve program semantics and proved to be more robust than ad-hoc non-verified compilers. The og al of the dissertation is to make a step towards verifying an industrial strength modern compiler-- LLVM, which has a typed, SSA-based, and general-purpose intermediate representation, therefore allowing more advanced program transformations than existing approaches. The dissertation formally defines the sequential semantics of the LLVM intermediate representation with its type system, SSA properties, memory model, and operational semantics.
    [Show full text]
  • Compiler-Based Code-Improvement Techniques
    Compiler-Based Code-Improvement Techniques KEITH D. COOPER, KATHRYN S. MCKINLEY, and LINDA TORCZON Since the earliest days of compilation, code quality has been recognized as an important problem [18]. A rich literature has developed around the issue of improving code quality. This paper surveys one part of that literature: code transformations intended to improve the running time of programs on uniprocessor machines. This paper emphasizes transformations intended to improve code quality rather than analysis methods. We describe analytical techniques and specific data-flow problems to the extent that they are necessary to understand the transformations. Other papers provide excellent summaries of the various sub-fields of program analysis. The paper is structured around a simple taxonomy that classifies transformations based on how they change the code. The taxonomy is populated with example transformations drawn from the literature. Each transformation is described at a depth that facilitates broad understanding; detailed references are provided for deeper study of individual transformations. The taxonomy provides the reader with a framework for thinking about code-improving transformations. It also serves as an organizing principle for the paper. Copyright 1998, all rights reserved. You may copy this article for your personal use in Comp 512. Further reproduction or distribution requires written permission from the authors. 1INTRODUCTION This paper presents an overview of compiler-based methods for improving the run-time behavior of programs — often mislabeled code optimization. These techniques have a long history in the literature. For example, Backus makes it quite clear that code quality was a major concern to the implementors of the first Fortran compilers [18].
    [Show full text]
  • Design and Implementation of a PHP Compiler Front-End
    Design and Implementation of a PHP Compiler Front-end Edsko de Vries∗ and John Gilbert fdevriese, [email protected] Department of Computer Science School of Computer Science and Statistics Trinity College Dublin, Ireland September 21, 2007 Abstract This technical report describes the design and implementation of a front-end for phc, the open source PHP compiler. This front-end provides an excellent basis for developing tools which process PHP source code, and consists of a well-defined Abstract Syntax Tree (AST) specification for the PHP language, a lexical analyser and parser which construct the AST for a given script, and a visitor and transformation API for manipulating these ASTs. 1 Introduction PHP [1] is a dynamically typed general purpose scripting language which can be embedded in HTML pages. It was designed in 1995 for implementing dynamic web pages, its name initially standing for Personal Home Pages. PHP now stands for the recursive acronym PHP: Hypertext Preprocessor. While predominantly used for server-side scripting PHP can be used for writing command line scripts and client-side GUI applications. It may also be embedded into host applications to provide them with scripting functionality. The main implementation of PHP is free open source software. This provides the de facto definition of the syntax and semantics for the language since there is no formal specification. While the end user interface and extensions API for the PHP interpreter are well documented [2, 10], scant documentation exists for the internals of the parser and the Zend engine (which interprets scripts). The lexical analyser is defined using a Flex description of 2000 lines, and the parser a Bison specification of 900 lines.
    [Show full text]