Intel® ISA Extensions
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micro operations

zhangxiuxia
Beginner
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Today I use iaca(a tool to analysis code), I find that the instruction "molvpd" and "movupd"
has difference numbers of uops .
the following is the instrucion I used in my assembly (AT&T style)

movlpd %mm1,(%rdx,%rcx,8)
movupd %mm1,(%rdx,%rcx,8)

movupd has 1 uops, while movlpd has 2 .
movlpd accupied port2(load port) and port 5(SIMD ALU).
I wonder why it occupied port 5?
I thinks the two instruction are almost the same .
but the result is they are not the same.
Why this could happend?


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Thomas_W_Intel
Employee
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One difference is that for movlpd, "the high quadword of the xmm register remains unchanged", i.e. partof the old register value is still needed. How this is implemented depends on the micro-architecture.

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