On: “C is how the computer works” is a dangerous mindset for C programmers

[vardump]

Microcode on x86? Don't forget to also greet our friends such as RDTSCP, CPUID, RDMSR, POPCNT (on some models) etc. Also remember to check ENTER, BOUND, etc. out in the museum vitrine.

But yeah, microcoded instructions are relatively rarely executed.

[Jasper_ → vardump]

I can't find any evidence that RDTSCP is microcoded. That would defeat the whole purpose of a high-performance counter. Any source?

[PeCaN → Jasper_]

Agner Fog's instruction tables list it as issuing ~23 fused uops (a bit more or fewer depending on generation) and a throughput of 1 per ~32 cycles. That seems like it could be microcoded.

[vardump → Jasper_]

I can't find any primary source, but I'm pretty sure about it.