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Data-flow Analysis
Data-flow analysis is a technique for gathering information about the possible set of values calculated at various points in a computer program. It forms the foundation for a wide variety of compiler optimizations and program verification techniques. A program's control-flow graph (CFG) is used to determine those parts of a program to which a particular value assigned to a variable might propagate. The information gathered is often used by compilers when optimizing compiler, optimizing a program. A canonical example of a data-flow analysis is reaching definitions. Other commonly used data-flow analyses include live variable analysis, available expressions, constant propagation, and very busy expressions, each serving a distinct purpose in compiler optimization passes. A simple way to perform data-flow analysis of programs is to set up data-flow equations for each node (computer science), node of the control-flow graph and solve them by repeatedly calculating the output from the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Live Variable Analysis
In compilers, live variable analysis (or simply liveness analysis) is a classic data-flow analysis to calculate the variables that are ''live'' at each point in the program. A variable is ''live'' at some point if it holds a value that may be needed in the future, or equivalently if its value may be read before the next time the variable is written to. Example Consider the following program: b = 3 c = 5 a = f(b * c) The set of live variables between lines 2 and 3 is because both are used in the multiplication on line 3. But the set of live variables after line 1 is only , since variable c is updated later, on line 2. The value of variable a is not used in this code. Note that the assignment to a may be eliminated as a is not used later, but there is insufficient information to justify removing all of line 3 as f may have side effects (printing b * c, perhaps). Expression in terms of dataflow equations Liveness analysis is a "backwards may" analysis. The analysis is done ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Computer Program
A computer program is a sequence or set of instructions in a programming language for a computer to Execution (computing), execute. It is one component of software, which also includes software documentation, documentation and other intangible components. A ''computer program'' in its human-readable form is called source code. Source code needs another computer program to Execution (computing), execute because computers can only execute their native machine instructions. Therefore, source code may be Translator (computing), translated to machine instructions using a compiler written for the language. (Assembly language programs are translated using an Assembler (computing), assembler.) The resulting file is called an executable. Alternatively, source code may execute within an interpreter (computing), interpreter written for the language. If the executable is requested for execution, then the operating system Loader (computing), loads it into Random-access memory, memory and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Tree (graph Theory)
In graph theory, a tree is an undirected graph in which any two vertices are connected by path, or equivalently a connected acyclic undirected graph. A forest is an undirected graph in which any two vertices are connected by path, or equivalently an acyclic undirected graph, or equivalently a disjoint union of trees. A directed tree, oriented tree,See .See . polytree,See . or singly connected networkSee . is a directed acyclic graph (DAG) whose underlying undirected graph is a tree. A polyforest (or directed forest or oriented forest) is a directed acyclic graph whose underlying undirected graph is a forest. The various kinds of data structures referred to as trees in computer science have underlying graphs that are trees in graph theory, although such data structures are generally rooted trees. A rooted tree may be directed, called a directed rooted tree, either making all its edges point away from the root—in which case it is called an arborescence or out-tree� ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Available Expression
In the field of compiler optimizations, available expressions is an analysis algorithm that determines for each point in the program the set of expressions that need not be recomputed. Those expressions are said to be ''available'' at such a point. To be available on a program point, the operands of the expression should not be modified on any path from the occurrence of that expression to the program point. The analysis is an example of a forward data flow analysis problem. A set of available expressions is maintained. Each statement is analysed to see whether it changes the operands of one or more available expressions. This yields sets of available expressions at the end of each basic block In compiler construction, a basic block is a straight-line code sequence with no branches in except to the entry and no branches out except at the exit. This restricted form makes a basic block highly amenable to analysis. Compilers usually decom ..., known as the outset in data flow anal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Bit Array
A bit array (also known as bitmask, bit map, bit set, bit string, or bit vector) is an array data structure that compactly stores bits. It can be used to implement a simple set data structure. A bit array is effective at exploiting bit-level parallelism in hardware to perform operations quickly. A typical bit array stores ''kw'' bits, where ''w'' is the number of bits in the unit of storage, such as a byte or Word (computer architecture), word, and ''k'' is some nonnegative integer. If ''w'' does not divide the number of bits to be stored, some space is wasted due to Fragmentation (computing), internal fragmentation. Definition A bit array is a mapping from some domain (almost always a range of integers) to values in the set . The values can be interpreted as dark/light, absent/present, locked/unlocked, valid/invalid, et cetera. The point is that there are only two possible values, so they can be stored in one bit. As with other arrays, the access to a single bit can be managed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Use Case
In both software and systems engineering, a use case is a structured description of a system’s behavior as it responds to requests from external actors, aiming to achieve a specific goal. It is used to define and validate functional requirements A use case is a list of actions or event steps typically defining the interactions between a role (known in the Unified Modeling Language (UML) as an ''actor'') and a system to achieve a goal. The actor can be a human or another external system. In systems engineering, use cases are used at a higher level than within software engineering, often representing missions or stakeholder goals. The detailed requirements may then be captured in the Systems Modeling Language (SysML) or as contractual statements. Differences between Systems and Software Engineering Use Cases In software engineering, the use case defines potential scenarios of the software in response to an external request (such as user input). In systems engineering, a use c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Requirement
In engineering, a requirement is a condition that must be satisfied for the output of a work effort to be acceptable. It is an explicit, objective, clear and often quantitative description of a condition to be satisfied by a material, design, product, or service. A specification or spec is a set of requirements that is typically used by developers in the design stage of new product development, product development and by testers in their verification process. With iterative and incremental development such as agile software development, requirements are developed in parallel with design and implementation. With the waterfall model, requirements are completed before design or implementation start. Requirements are used in many engineering fields including engineering design, system engineering, software engineering, enterprise engineering, New product development, product development, and process optimization. Requirement is a relatively broad concept that can describe any nec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Software Feature
A feature is "a prominent or distinctive user-visible aspect, quality, or characteristic of a software system or systems", as defined by Kang et al. At the implementation level, "it is a structure that extends and modifies the structure of a given software in order to satisfy a stakeholder’s requirement, to implement and encapsulate a design decision, and to offer a configuration option", as defined by Apel et al. Context The term feature means the same for software as it does for any kind of system. For example, the British Royal Navy's HMS Dreadnought (1906) was considered an important milestone in naval technology because of its advanced features that did not exist in pre-dreadnought battleships. Feature also applies to computer hardware. In the early history of computers, devices such as Digital Equipment Corporation's PDP-7 minicomputer (created in 1964) was noted for having a wealth of features, such as being the first version of the PDP minicomputer series to us ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Control Flow Analysis
In computer science, control-flow analysis (CFA) is a static-code-analysis technique for determining the control flow of a program. The control flow is expressed as a control-flow graph (CFG). For both functional programming languages and object-oriented programming languages, the term CFA, and elaborations such as ''k''-CFA, refer to specific algorithms that compute control flow. For many imperative programming languages, the control flow of a program is explicit in a program's source code. As a result, interprocedural control-flow analysis implicitly usually refers to a static analysis technique for determining the receivers of function or method calls in computer programs written in a higher-order programming language. For example, in a programming language with higher-order functions like Scheme, the target of a function call may not be explicit: in the isolated expression (lambda (f) (f x)) it is unclear to which procedure f may refer. A control-flow analysis must ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Abstract Interpretation
In computer science, abstract interpretation is a theory of sound approximation of the semantics of computer programs, based on monotonic functions over ordered sets, especially lattices. It can be viewed as a partial execution of a computer program which gains information about its semantics (e.g., control-flow analysis, control-flow, data-flow analysis, data-flow) without performing all the calculations. Its main concrete application is formal static code analysis, static analysis, the automatic information extraction, extraction of information about the possible executions of computer programs; such analyses have two main usages: * inside compilers, to analyse programs to decide whether certain Optimization (computer science), optimizations or Program transformation, transformations are applicable; * for debugging or even the certification of programs against classes of bugs. Abstract interpretation was formalized by the French computer scientist working couple Patrick Cousot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Static Single-assignment Form
In compiler design, static single assignment form (often abbreviated as SSA form or simply SSA) is a type of intermediate representation (IR) where each variable is assigned exactly once. SSA is used in most high-quality optimizing compilers for imperative languages, including LLVM, the GNU Compiler Collection, and many commercial compilers. There are efficient algorithms for converting programs into SSA form. To convert to SSA, existing variables in the original IR are split into versions, new variables typically indicated by the original name with a subscript, so that every definition gets its own version. Additional statements that assign to new versions of variables may also need to be introduced at the join point of two control flow paths. Converting from SSA form to machine code is also efficient. SSA makes numerous analyses needed for optimizations easier to perform, such as determining use-define chains, because when looking at a use of a variable there is only one place ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Dead Code Elimination
In compiler theory, dead-code elimination (DCE, dead-code removal, dead-code stripping, or dead-code strip) is a compiler optimization to remove dead code (code that does not affect the program results). Removing such code has several benefits: it shrinks executable, program size, an important consideration in some contexts, it reduces resource usage such as the number of bytes to be transferredMalavolta, Ivano et al. “JavaScript Dead Code Identification, Elimination, and Empirical Assessment.” IEEE transactions on software engineering 49.7 (2023): 3692–3714. Web. and it allows the running program to avoid executing irrelevant CPU instruction, operations, which reduces its execution (computing), running time. It can also enable further optimizations by simplifying program structure. Dead code includes code that can never be executed (unreachable code), and code that only affects dead variables (written to, but never read again), that is, irrelevant to the program. Examples C ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |