Loop fission
Loop fission is a code transformation technique that works by splitting a loop into multiple loops over the same index range, each one taking only a part of the original loop body. The goal is to isolate statements that can take advantage of compiler and hardware optimizations, separating them from other statements preventing those optimizations. It is worth exploring the application of loop fission in codes with the following features:
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Loop-carried dependencies between statements of the loop - e.g. when the data needed in the current iteration of the loop depends on the data from the previous iteration of the loop.
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Conditional statements in the loop body that depend on the data - e.g. when conditional statements in the loop body depend on input data, the execution path of the code cannot be anticipated and performance optimizations may be disabled at run-time.
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Non-sequential memory accesses in the loop - e.g. non-sequential memory accesses do not exhibit good locality of reference, thus the code does not take full advantage of the hardware cache memory and compiler optimizations may be disabled.
Loop fission enables more efficient code by taking advantage of memory efficiency, vectorization and offloading to accelerators.
Loop fission introduces overheads (e.g. loop control increment and branching), so in general it is necessary to run and benchmark the code to determine if loop fission brings performance gain.