[OT] End-user uses for x86-64 (was: Why are still not at 64 bits)

[Bill McGonigle]

On Feb 16, 2007, at 13:44, Ben Scott wrote:

>  One is my understanding: Even if you're working with a 64-bit
> architecture, isn't most software still dealing with 32-bit values?
> Does throughput double without re-writing all the code to take
> advantage of that?

I recall reading somewhere [I'll never find the reference, I'm sure]  
that there were some compiler optimizations to take two 32-bit ops  
(say in a loop) and optimize them into a single 64-bit op.  These  
depend on conditions that have been predicted a priori, though, like  
loop optimization.   And you'd have to assume that loading four ops  
into, say, an SSE3  unit, wouldn't be a better way to spend time.

I'm not sure what kind of operations would benefit from doing 2 at a  
time rather than 4 at a time.  My first reaction would be IEEE  
floating point or something with hardware assist that can't be fed  
into an integer vector processor.  But I'm consciously avoiding  
thinking about the binary representation of this because that kind of  
thing usually just results in neuronal injury on a Friday evening.

-Bill
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