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1052 Discussions

Are instruction ups of an instruction be issued at the same time ?

zhangxiuxia
Beginner
151 Views
some instruction are decocded into more than one uops , such as memory operand arithmetic ,
mulsd (%rsi,%rax,8), %xmm1
are decoded into one mov uop and one mul uop.

I wonder whether the two uop be issued at the same time ?
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3 Replies
Maxym_D_Intel
Employee
151 Views
have a look at Intel 64 and IA-32 Architectures Optimization Reference Manual
there are chapters that describe details of decode step, like "2.2.2.4 Instruction Decode",
for example, quote:
The microsequencer can provide up to 3 ops per cycle, and helps decode instructions larger than 4 ops

Max_L
Employee
151 Views

it depends on what you mean by "issued" - they cannot be executed at the same time,as mul needs data to be loaded first by the load uop,it is the scheduler, aka RS(Reservation Station), that receives uops after the decode and is responsible for triggering uops to go to execution onceuop's sources are (or expected to be) ready.

-Max

zhangxiuxia
Beginner
151 Views
I understand. Thank you, Max.
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