80386 Early Start Memory Access

Intel's 80386 processor used an "Early Start" technique to hide memory latency by beginning the next instruction's address calculation during the final cycle of the current instruction, contributing approximately 9% to overall performance. The z386 FPGA core implementation of the 386 microcode added this Early Start optimization along with other improvements, achieving ao486-class performance with Doom frame rates jumping 39% (from 16.6 to 23.0 FPS) at the same 85 MHz clock speed by reducing cycles per instruction. The optimization works by leveraging a forwarding network to detect register dependencies and overlap instruction execution stages, though Intel's original implementation had a corner-case bug in this forwarding logic that caused the famous POPAD bug.