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In computer science, instruction scheduling is a compiler optimization used to improve instruction-level parallelism, which improves performance on machines with instruction pipelines. Put more simply, it tries to do the following without changing the meaning of the code:
The first machine to use out-of-order execution was the CDC 6600 (1964), designed by James E. Thornton, which uses a scoreboard to avoid conflicts. It permits an instruction to execute if its source operand (read) registers aren't to be written to by any unexecuted earlier instruction (true dependency) and the destination (write) register not be a register used by any unexecuted earlier ...
In computer science, instruction selection is the stage of a compiler backend that transforms its middle-level intermediate representation (IR) into a low-level IR. In a typical compiler, instruction selection precedes both instruction scheduling and register allocation; hence its output IR has an infinite set of pseudo-registers (often known as temporaries) and may still be – and typically ...
Execution in computer and software engineering is the process by which a computer or virtual machine interprets and acts on the instructions of a computer program.Each instruction of a program is a description of a particular action which must be carried out, in order for a specific problem to be solved.
The instruction window has a finite size, and new instructions can enter the window (usually called dispatch or allocate) only when other instructions leave the window (usually called retire or commit). Instructions enter and leave the instruction window in program order, and an instruction can only leave the window when it is the oldest ...
The average of Cycles Per Instruction in a given process (CPI) is defined by the following weighted average: := () = () Where is the number of instructions for a given instruction type , is the clock-cycles for that instruction type and = is the total instruction count.
Generating position-independent code is often the default behavior for compilers, but they may place restrictions on the use of some language features, such as disallowing use of absolute addresses (position-independent code has to use relative addressing). Instructions that refer directly to specific memory addresses sometimes execute faster ...
Instruction-level parallelism (ILP) is the parallel or simultaneous execution of a sequence of instructions in a computer program. More specifically, ILP refers to the average number of instructions run per step of this parallel execution.