Eliminating Go bounds checks with unsafe

7 days ago

Unsafe pointer arithmetic can be used in Go to eliminate bound checks that the compiler cannot remove, provided the programmer can prove they are unnecessary.
Bound checks elimination (BCE) reduces instructions and branches, improving performance by lowering cache misses, register pressure, and wasted cycles.
Go's compiler adds bound checks to prevent out-of-range slice accesses, which can be identified using the -gcflags='-d=ssa/check_bce/debug=1' flag.
Conventional BCE methods include hinting the compiler by accessing bounds first, but unsafe techniques are needed when the compiler cannot infer safety.
An unsafe alternative to binary.LittleEndian.Uint32, using unsafe.SliceData and unsafe.Add, eliminates all bound checks and significantly boosts performance in benchmarks.

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