Barcelona optimization guide

By: anonymous (anonymous.delete@this.anonymous.com), May 12, 2007 6:47 am
Room: Moderated Discussions
Sometimes you need a unaligned load...
Barcelona is bottlenecked by it's decoders to 3 macro-ops per cicle, so if you take a good look at the manual you will notice it says to use load-exec instructions as much as possible to reduce the number of macro-ops.
Now, when you must use a unaligned load, you can use a single load-exec instruction, instead of a LDUDQ and a op instruction.

anonymous (no@spam.com) on 5/12/07 wrote:
---------------------------
>>It seems likely to me that this means most folks will ignore the unaligned SSE
>>LD capability in Barcelona as a result. Intel won't be adding that for a while...
>
>Considering that people have been "trained" to align SSE
>data, I wonder how critical misaligned SSE support really
>is. In other words: is it a side effect of K8L's widened
>load ports, or did lots of folks demand it? (I also noted
>that the K8L optimization guide still claims that aligned
>SSE data is faster than unaligned one.)
>
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