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Reference.org
Instruction scheduling
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<p>In <a href="/facts/Computer_science/lN3pEyPz">computer science</a>, instruction scheduling is a <a href="/facts/Compiler_optimization/JXnv4LUd">compiler optimization</a> used to improve <a href="/facts/Instruction-level_parallelism/2W8qvN8K">instruction-level parallelism</a>, which improves performance on machines with <a href="/facts/Instruction_pipeline/3zy6CcX1">instruction pipelines</a>. Put more simply, it tries to do the following without changing the meaning of the code: </p> <ul><li>Avoid <a href="/facts/Pipeline_stall/e3Ee0yJg">pipeline stalls</a> by rearranging the order of instructions.</li> <li>Avoid illegal or semantically ambiguous operations (typically involving subtle instruction pipeline timing issues or non-interlocked resources).</li></ul> <p>The pipeline stalls can be caused by structural hazards (processor resource limit), data hazards (output of one instruction needed by another instruction) and control hazards (branching). </p>