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[Web] Analysis: x86 Vs PPCANN.lu
Posted on 09-Jul-2003 21:21 GMT by Hagge38 comments
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Analysis: x86 Vs PPC : Comment 34 of 38ANN.lu
Posted by Chain|Q on 11-Jul-2003 15:31 GMT
In reply to Comment 25 (Megol):
"The overhead is not that great in practice as (using Athlon as an example) the swap instruction is treated as a FNOP(==Floating point No OPeration)"

Yes, on Athlon it takes zero clocks to execute this in the ideal case. Just like on Pentium/PPro/PII/PIII. But it's not the case on older x86's, and other x86-clone CPU's like the K6 & co, and also not true for Intel Pentium 4!!! And i just think this is still a good example of the hack&patches made on the terrible ISA to be somewhat more effective...

"and the x86 can use memory operands to replace register accesses.
So your code above would translate to (if 'fp2's value is first on the stack):"

_IF_ it's there... In most cases it doesn't so you've to swap, which makes code less readable, and results in slowdowns. Also using memory operands generate more load on the bus -> reduces efficiency, since in most cases you'll do more operations on a single value... Also if the required value is not in the cache, you might got some nasty pipe stalls and like that. Simply too much limitations, it's a PITA as you said... :]

"Well the x86 FPUs still are among the most effective for microprocessors."

In fact, i'd rather call them fast, than effective. Since they're fast that's unquestionable, but not effective, because they waste more resources to archieve the same speed levels of other CPU's, just because the ugly architecture and brain-damaged design of the ISA... This is why they produce more heat, and stuff like that, already discussed in the quoted articles.
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Comment 35Joe "Floid" Kanowitz11-Jul-2003 18:05 GMT
Comment 36smp26612-Jul-2003 01:00 GMT
Comment 37Anonymous14-Jul-2003 18:17 GMT
Comment 38Anonymous14-Jul-2003 18:18 GMT
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