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From: BGB <cr88192@gmail.com>
Newsgroups: comp.arch
Subject: Re: Oops (Concertina II Going Around in Circles)
Date: Fri, 10 May 2024 16:16:28 -0500
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On 5/10/2024 2:51 PM, John Dallman wrote:
> In article <be3r3jhr1kf9n1cdsbik5ejsuso7c3pmmk@4ax.com>,
> quadibloc@servername.invalid (John Savard) wrote:
> 
>> On Fri, 10 May 2024 00:19 +0100 (BST), jgd@cix.co.uk (John Dallman)
>> wrote:
>>
>>> Not that justified the costs of implementing such a huge
>>> instruction set.
>>
>> Well, having a huge instruction set defined and implementing all of
>> it are two different things.
>>
>> Look at x86, how MMX got replaced by SSE which got replaced by AVX.
>>
>> So if one is going to include instructions that will later become
>> obsolete, and be replaced by other instructions, not re-using the
>> same opcodes helps with upwards compatibility.
> 
> Intel did not re-use the opcodes. MMX, SSE, SSE2 and so on are all still
> implemented and usable. Once a hardware feature has been used in software,
> getting rid of it is hard. I'm still building x86-32 software for SSE2
> because AVX[2] doesn't do anything useful for it.
> 

In my experience, SSE2 is still preferable as enabling AVX tends to come 
with a fairly obvious performance hit (particularly with MSVC's fairly 
aggressive use of auto vectorization).


> John