Instruction-Level Parallelism (ILP)
TLDR: Instruction Level Parallelism (ILP) refers to the ability of a processor to execute multiple instructions simultaneously by exploiting the independence of operations within a single instruction stream. This is achieved through techniques like superscalar execution, out-of-order execution, and pipelining. ILP enhances the performance of sequential programs by increasing throughput without requiring changes to the program’s structure.
https://en.wikipedia.org/wiki/Instruction-level_parallelism
Modern processors implement ILP using advanced hardware features. Superscalar execution enables a CPU to dispatch multiple instructions to different functional units (e.g., ALU, FPU) in a single clock cycle. Out-of-order execution dynamically reorders instructions to maximize utilization of hardware resources while preserving program correctness. Branch prediction and speculative execution further optimize ILP by reducing pipeline stalls caused by control dependencies.
https://www.intel.com/content/www/us/en/architecture-and-technology/branch-prediction.html
While ILP significantly improves single-threaded performance, it is limited by factors like data dependencies and pipeline hazards. Techniques such as register renaming and loop unrolling help mitigate these bottlenecks, enabling more efficient parallel execution. However, as workloads become increasingly multi-threaded, ILP complements other forms of parallelism, such as thread-level parallelism (TLP), to deliver comprehensive performance gains in modern processors.