Quadrupling code performance with a "useless" if
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Performance optimization trick with a 'useless' if, technically deep and actionable.
Summary
A 'useless' if statement that checks whether j equals next_j[i][j] can quadruple loop performance by enabling CPU branch prediction to break data dependencies. In a domain-specific compressor, the loop's single mov instruction was latency-bound due to pointer chasing; adding an unlikely branch allowed speculative execution, reducing runtime from 320µs to 80µs. The technique requires compiler hints like [[unlikely]] or volatile to prevent optimization removal.