[jeffbee]

This may surprise you but large CPU buyers go to Intel and ask for ISA extensions, and Intel implements them. This is how BMI came to exist. The fact that you do not see these instructions exploited by your vanilla Debian box says nothing about warehouse-scale datacenter operators.

[xoranth]

Your vanilla Debian box uses BMI2 whenever you do a string comparison, unless you are on a decade old CPU [^0].

The "strange" instructions are actually not that niche, it's just that usage tends to be "indirect" and therefore people don't notice.

[^0] E.g. https://xoranth.net/memcmp-avx2

[paulmd]

Yes. AVX-512 support is also implemented by SIMD-JSON. JSON string parsing, definitely not a thing anybody does. /s

Also super great for emulation, and anyone else who does a lot of bulk bit-twiddling.

The whole discourse has become super weird (up to and including Linux himself ;) because of Intel 10nm delays. With the only AVX-512 products being 14nm-based intel server chips for 5 years, and then only coming to laptop for another couple years, and then only a single terrible generation of desktop parts that nobody bought, and with AMD launching super competitive (usually leading) products in those segments, obviously there wasn't a whole lot of real consistent adoption in software. And what adoption there was, was complicated by the fact that the largest adopter (server market) had to drop clocks massively and even pause processing to allow voltage to swing up enough, because they were 14nm products on a feature that was really aimed at 10nm and beyond. And then Intel yanked it out of all the desktop and laptop chips and seems poised to just ignore it for another 5 years.

Everyone just decided that because it wasn't getting adopted that it was inherently useless, up to and including Linus himself. But it wasn't getting adopted because it was a complete mess on the Intel side and AMD didn't even support it, so why bother?

The AVX-512 story is inextricably bound up in the 10nm delays and the organizational problems that have plagued Intel ever since. It's such a great thing that AMD didn't buy into the naysaying.

[foobiekr]

Famously, popcount was a common request from intelligence agencies, at least as far back as the DEC Alpha.