Re: Oops (Concertina II Going Around in Circles)

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