Intel says that:
> Micro-fusion fuses multiple micro-ops from the same instruction into a single complex micro-op.
And that:
> Macro-fusion merges two instructions to a single micro-op.
The point is that the three instruction format and the single instruction format you would think would decode both to three micro-ops (or something like that), but instead the single instruction format can use a single fused micro op. That's why it's better to write as a single instruction.
And your reference backs this up - it talks about single instructions in this section on micro-op fusion.
You may be confusing it with macro-fusion, which is about fusing multiple logical instructions, which is discussed in the next section in that Agner document, but isn't discussed in this blog.
> This article is instead about whether a particular operation is better written as a single-instruction
Yes - it's better to write as a single-instruction, because then micro-op fusion applies. Macro-op fusion isn't as strong, as doesn't apply to the three logical instructions.
> Micro-fusion fuses multiple micro-ops from the same instruction into a single complex micro-op.
And that:
> Macro-fusion merges two instructions to a single micro-op.
The point is that the three instruction format and the single instruction format you would think would decode both to three micro-ops (or something like that), but instead the single instruction format can use a single fused micro op. That's why it's better to write as a single instruction.
And your reference backs this up - it talks about single instructions in this section on micro-op fusion.
You may be confusing it with macro-fusion, which is about fusing multiple logical instructions, which is discussed in the next section in that Agner document, but isn't discussed in this blog.
> This article is instead about whether a particular operation is better written as a single-instruction
Yes - it's better to write as a single-instruction, because then micro-op fusion applies. Macro-op fusion isn't as strong, as doesn't apply to the three logical instructions.