|
Enabling Transformation
In computer science, an enabling transformation is a compiler optimization that increases the effectiveness of other compiler optimizations. Such an optimization may or may not improve program performance by itself, but it also alters the structure of the program in such a way that other optimizations may produce superior results. Typical enabling transformations include: * Inline expansion: By inserting the body of a function in place of its call site, a large collection of intraprocedural optimizations such as dead code elimination, loop-invariant code motion, and induction variable elimination can take advantage of information from both the caller and callee. * Loop skewing: By "skewing" the logical shape of an array, this loop optimization can (when combined with loop interchange) eliminate loop-carried dependencies, allowing an inner loop to be parallelized. * Loop unswitching moves loop invariant In computer science, a loop invariant is a property of a program loop tha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Science
Computer science is the study of computation, information, and automation. Computer science spans Theoretical computer science, theoretical disciplines (such as algorithms, theory of computation, and information theory) to Applied science, applied disciplines (including the design and implementation of Computer architecture, hardware and Software engineering, software). Algorithms and data structures are central to computer science. The theory of computation concerns abstract models of computation and general classes of computational problem, problems that can be solved using them. The fields of cryptography and computer security involve studying the means for secure communication and preventing security vulnerabilities. Computer graphics (computer science), Computer graphics and computational geometry address the generation of images. Programming language theory considers different ways to describe computational processes, and database theory concerns the management of re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Compiler Optimization
An optimizing compiler is a compiler designed to generate code that is optimized in aspects such as minimizing program execution time, memory usage, storage size, and power consumption. Optimization is generally implemented as a sequence of optimizing transformations, a.k.a. compiler optimizations algorithms that transform code to produce semantically equivalent code optimized for some aspect. Optimization is limited by a number of factors. Theoretical analysis indicates that some optimization problems are NP-complete, or even undecidable. Also, producing perfectly ''optimal'' code is not possible since optimizing for one aspect often degrades performance for another. Optimization is a collection of heuristic methods for improving resource usage in typical programs. Categorization Local vs. global scope Scope describes how much of the input code is considered to apply optimizations. Local scope optimizations use information local to a basic block. Since basic blocks cont ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inline Expansion
In computing, inline expansion, or inlining, is a manual or compiler optimization that replaces a function call site with the body of the called function. Inline expansion is similar to macro expansion, but occurs during compiling, without changing the source code (the text), while macro expansion occurs before compiling, and results in different text that is then processed by the compiler. Inlining is an important optimization, but has complex effects on performance. As a rule of thumb, some inlining will improve speed at very minor cost of space, but excess inlining will hurt speed, due to inlined code consuming too much of the instruction cache, and also cost significant space. A survey of the modest academic literature on inlining from the 1980s and 1990s is given in Peyton Jones & Marlow 1999. Overview Inline expansion is similar to macro expansion as the compiler places a new copy of the function in each place it is called. Inlined functions run a little faster than the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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] |
Loop-invariant Code Motion
In computer programming, loop-invariant code consists of statements or expressions (in an imperative programming, imperative programming language) that can be moved outside the body of a loop without affecting the semantics of the program. Loop-invariant code motion (also called hoisting or scalar promotion) is a compiler optimization that performs this movement automatically. Example In the following code sample, two optimizations can be applied. int i = 0; while (i < n) Although the calculation x = y + z and x * x is loop-invariant, precautions must be taken before moving the code outside the loop. It is possible that the loop condition is false (for example, if n holds a negative value), and in such case, the loop body should not be executed at all. One way of guaranteeing correct behaviour is using a conditional branch outside of the loop. Evaluating the loop condition can have Side effect (computer sci ...
[...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Induction Variable Elimination
In computer science, an induction variable is a variable that gets increased or decreased by a fixed amount on every iteration of a loop or is a linear function of another induction variable. For example, in the following loop, i and j are induction variables: for (i = 0; i < 10; ++i) Application to strength reduction A common is to recognize the existence of induction variables and replace them with simpler computations; for example, the code above could be rewritten by the compiler as follows, on the assumption that the addition of a constant will be cheaper than a multiplication. |
Loop Skewing
The polyhedral model (also called the polytope method) is a mathematical framework for programs that perform large numbers of operations -- too large to be explicitly enumerated -- thereby requiring a ''compact'' representation. Nested loop programs are the typical, but not the only example, and the most common use of the model is for loop nest optimization in program optimization. The polyhedral method treats each loop iteration within nested loops as lattice points inside mathematical objects called polytope, polyhedra, performs affine transformations or more general non-affine transformations such as Loop tiling, tiling on the polytopes, and then converts the transformed polytopes into equivalent, but optimized (depending on targeted optimization goal), loop nests through polyhedra scanning. Simple example Consider the following example written in C (programming language), C: const int n = 100; int i, j; int a[n][n] = ; for (i = 1; i < n; i++) for (i = 0; i < n; i++) [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Loop Interchange
Loop or LOOP may refer to: Brands and enterprises * Loop (mobile), a Bulgarian virtual network operator and co-founder of Loop Live * Loop, clothing, a company founded by Carlos Vasquez in the 1990s and worn by Digable Planets * Loop Mobile, an Indian mobile phone operator * Loop Internet, an internet service provider in Pennsylvania, United States * Loop, a reusable container program announced in 2019 by TerraCycle Geography * Loop, Germany, a municipality in Schleswig-Holstein * Loop (Texarkana), a roadway loop around Texarkana, Arkansas, United States * Loop, Blair County, Pennsylvania, United States * Loop, Indiana County, Pennsylvania, United States * Loop, West Virginia, United States * Loop 101, a semi-beltway of the Phoenix Metropolitan Area * Loop 202, a semi-beltway of the Phoenix Metropolitan Area * Loop 303, a semi-beltway of the Phoenix Metropolitan Area * Chicago Loop, the downtown neighborhood of Chicago bounded by the elevated railway The Loop ** L ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Loop Dependence Analysis
In computer science, loop dependence analysis is a process which can be used to find dependencies within iterations of a loop with the goal of determining different relationships between statements. These dependent relationships are tied to the order in which different statements access memory locations. Using the analysis of these relationships, execution of the loop can be organized to allow multiple processors to work on different portions of the loop in parallel. This is known as parallel processing. In general, loops can consume a lot of processing time when executed as serial code. Through parallel processing, it is possible to reduce the total execution time of a program through sharing the processing load among multiple processors. The process of organizing statements to allow multiple processors to work on different portions of a loop is often referred to as parallelization. In order to see how we can exploit parallelization, we have to first analyze the dependencies wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Loop Unswitching
Loop unswitching is a compiler optimization. It moves a conditional inside a loop outside of it by duplicating the loop's body, and placing a version of it inside each of the if and else clauses of the conditional. This can improve the parallelization of the loop. Since modern processors can operate quickly on vectors, this improvement increases the speed of the program. Here is a simple example. Suppose we want to add the two arrays ''x'' and ''y'' and also do something depending on the variable ''w''. We have the following C code: int i, w, x000 y000 for (i = 0; i < 1000; i++) The conditional inside this loop makes it difficult to safely parallelize this loop. When we unswitch the loop, this becomes: |
Loop Invariant
In computer science, a loop invariant is a property of a program loop that is true before (and after) each iteration. It is a logical assertion, sometimes checked with a code assertion. Knowing its invariant(s) is essential in understanding the effect of a loop. In formal program verification, particularly the Floyd-Hoare approach, loop invariants are expressed by formal predicate logic and used to prove properties of loops and by extension algorithms that employ loops (usually correctness properties). The loop invariants will be true on entry into a loop and following each iteration, so that on exit from the loop both the loop invariants and the loop termination condition can be guaranteed. From a programming methodology viewpoint, the loop invariant can be viewed as a more abstract specification of the loop, which characterizes the deeper purpose of the loop beyond the details of this implementation. A survey article covers fundamental algorithms from many areas of compu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
