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macro-fusion

Joining two neighbouring instructions, typically a compare and the conditional branch after it, into one micro-op inside the processor.

Macro-fusion decodes an adjacent instruction pair (on x86-64 cmp/test/add/sub/and followed by a jcc; on some ARM64 cores cmp+b.cond and others) into a single micro-op, saving decode, rename and retire bandwidth.

Examples

  • On recent Intel and AMD cores, cmp rax, rbx followed by jne can decode as a single micro-op.

See also

micro-op retirement conditional branch compare instruction
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