x86 opcodes can be 15 bytes long, that's how. At the expense of code density, and thus hurting PPA (Power, Performance and Area). Wildly variable opcode lengt

x86 opcodes can be 15 bytes long, that's how. At the expense of code density, and thus hurting PPA (Power, Performance and Area). Wildly variable opcode length does also complicate the decoder considerably, as it has to find where instructions start and end, an inherently serial operation, and yet decode enough of them to feed an n-wide pipeline.