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Loop Inversion
In computer science, loop inversion is a compiler optimization and loop transformation in which a while loop is replaced by an if block containing a do..while loop. When used correctly, it may improve performance due to instruction pipelining or avoiding jump instructions to reduce branch mis-prediction. Example in Java void pre_inversion() is equivalent to: void post_inversion() No change in performance occurs for initial and non-final iterations through the loop, including when the loop is not entered because the condition is false. However, the final iteration has 2 fewer jump instructions when the loop is entered because the do-while loop does not need to jump to the start of the while loop to evaluate the loop condition. Example in C int i, a 00 i = 0; while (i = 100 goto L2 Let us assume that ''i'' had been initialized to some value less than 100. Now let us look at the instructions executed at the moment after ''i'' has been incremented to 99 in t ... [...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] |
Loop Transformation
In compiler theory, loop optimization is the process of increasing execution speed and reducing the overheads associated with loops. It plays an important role in improving cache performance and making effective use of parallel processing capabilities. Most execution time of a scientific program is spent on loops; as such, many compiler optimization techniques have been developed to make them faster. Representation of computation and transformations Since instructions inside loops can be executed repeatedly, it is frequently not possible to give a bound on the number of instruction executions that will be impacted by a loop optimization. This presents challenges when reasoning about the correctness and benefits of a loop optimization, specifically the representations of the computation being optimized and the optimization(s) being performed.In the book Reasoning About Program Transformations', Jean-Francois Collard discusses in depth the general question of representing exec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
While Loop
In most computer programming languages, a while loop is a control flow Statement (computer science), statement that allows code to be executed repeatedly based on a given Boolean data type, Boolean condition. The ''while'' loop can be thought of as a repeating Conditional (computer programming), if statement. Overview The ''while'' construct consists of a block of code and a condition/expression. The condition/expression is evaluated, and if the condition/expression is ''true'', the code within all of their following in the block is executed. This repeats until the condition/expression becomes False (logic), false. Because the ''while'' loop checks the condition/expression before the block is executed, the control structure is often also known as a pre-test loop. Compare this with the do while loop, ''do while'' loop, which tests the condition/expression ''after'' the loop has executed. For example, in the languages C (programming language), C, Java (programming language), Java ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
If Statement
In computer science, conditionals (that is, conditional statements, conditional expressions and conditional constructs) are programming language constructs that perform different computations or actions or return different values depending on the value of a Boolean expression, called a ''condition''. Conditionals are typically implemented by selectively executing instructions. Although dynamic dispatch is not usually classified as a conditional construct, it is another way to select between alternatives at runtime. Terminology Conditional statements are imperative constructs executed for side-effect, while conditional expressions return values. Many programming languages (such as C) have distinct conditional statements and conditional expressions. Although in pure functional programming, conditional expressions do not have side-effects, many languages with conditional expressions (such as Lisp) support conditional side-effects. If–then(–else) The if–then or if ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Do While Loop
In many computer programming Programming language, languages, a do while loop is a control flow Statement (computer science), statement that executes a block of code and then either repeats the block or exits the loop depending on a given Boolean data type, boolean condition. The ''do while'' construct consists of a process symbol and a condition. First the code within the block is executed. Then the condition is evaluated. If the condition is Truth, true the code within the block is executed again. This repeats until the condition becomes False (logic), false. Do while loops check the condition after the block of code is executed. This control structure can be known as a post-test loop. This means the do-while loop is an exit-condition loop. However a while loop will test the condition before the code within the block is executed. This means that the code is always executed first and then the expression or test condition is evaluated. This process is repeated as long as the ex ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Instruction Pipelining
In computer engineering, instruction pipelining is a technique for implementing instruction-level parallelism within a single processor. Pipelining attempts to keep every part of the processor busy with some instruction by dividing incoming instructions into a series of sequential steps (the eponymous "pipeline") performed by different processor units with different parts of instructions processed in parallel. Concept and motivation In a pipelined computer, instructions flow through the central processing unit (CPU) in stages. For example, it might have one stage for each step of the von Neumann cycle: Fetch the instruction, fetch the operands, do the instruction, write the results. A pipelined computer usually has "pipeline registers" after each stage. These store information from the instruction and calculations so that the logic gates of the next stage can do the next step. This arrangement lets the CPU complete an instruction on each clock cycle. It is common for even-nu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jump Instruction
A branch, jump or transfer is an instruction in a computer program that can cause a computer to begin executing a different instruction sequence and thus deviate from its default behavior of executing instructions in order. ''Branch'' (or ''branching'', ''branched'') may also refer to the act of switching execution to a different instruction sequence as a result of executing a branch instruction. Branch instructions are used to implement control flow in program loops and conditionals (i.e., executing a particular sequence of instructions only if certain conditions are satisfied). A branch instruction can be either an ''unconditional branch'', which always results in branching, or a ''conditional branch'', which may or may not cause branching depending on some condition. Also, depending on how it specifies the address of the new instruction sequence (the "target" address), a branch instruction is generally classified as ''direct'', ''indirect'' or ''relative'', meaning that the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Branch Predictor
In computer architecture, a branch predictor is a digital circuit that tries to guess which way a branch (e.g., an if–then–else structure) will go before this is known definitively. The purpose of the branch predictor is to improve the flow in the instruction pipeline. Branch predictors play a critical role in achieving high performance in many modern pipelined microprocessor architectures. Two-way branching is usually implemented with a conditional jump instruction. A conditional jump can either be "taken" and jump to a different place in program memory, or it can be "not taken" and continue execution immediately after the conditional jump. It is not known for certain whether a conditional jump will be taken or not taken until the condition has been calculated and the conditional jump has passed the execution stage in the instruction pipeline (see fig. 1). Without branch prediction, the processor would have to wait until the conditional jump instruction has passed the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Central Processing Unit
A central processing unit (CPU), also called a central processor, main processor, or just processor, is the primary Processor (computing), processor in a given computer. Its electronic circuitry executes Instruction (computing), instructions of a computer program, such as arithmetic, logic, controlling, and input/output (I/O) operations. This role contrasts with that of external components, such as main memory and I/O circuitry, and specialized coprocessors such as graphics processing units (GPUs). The form, CPU design, design, and implementation of CPUs have changed over time, but their fundamental operation remains almost unchanged. Principal components of a CPU include the arithmetic–logic unit (ALU) that performs arithmetic operation, arithmetic and Bitwise operation, logic operations, processor registers that supply operands to the ALU and store the results of ALU operations, and a control unit that orchestrates the #Fetch, fetching (from memory), #Decode, decoding and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Instruction Pipeline
In computer engineering, instruction pipelining is a technique for implementing instruction-level parallelism within a single processor. Pipelining attempts to keep every part of the processor busy with some instruction by dividing incoming Machine code, instructions into a series of sequential steps (the eponymous "Pipeline (computing), pipeline") performed by different Central processing unit#Structure and implementation, processor units with different parts of instructions processed in parallel. Concept and motivation In a pipelined computer, instructions flow through the central processing unit (CPU) in stages. For example, it might have one stage for each step of the von Neumann architecture, von Neumann cycle: Fetch the instruction, fetch the operands, do the instruction, write the results. A pipelined computer usually has "pipeline registers" after each stage. These store information from the instruction and calculations so that the logic gates of the next stage can do th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pipeline Stall
In the design of instruction pipeline, pipelined computer processors, a pipeline stall is a delay in execution of an instruction set, instruction in order to resolve a hazard (computer architecture), hazard. Details In a standard classic RISC pipeline#The classic five stage RISC pipeline, five-stage pipeline, during the classic RISC pipeline#Instruction decode, decoding stage, the control unit will determine whether the decoded instruction reads from a register to which the currently executed instruction writes. If this condition holds, the control unit will stall the instruction by one clock cycle. It also stalls the instruction in the fetch stage, to prevent the instruction in that stage from being overwritten by the next instruction in the program. In a Von Neumann architecture which uses the program counter (PC) register to determine the current instruction being fetched in the pipeline, to prevent new instructions from being fetched when an instruction in the decoding stage ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
