Proposal: @cpuid builtin

[data-man]

Possible new builtin:

@cpuid(id: u32,    // == EAX
       subId: u32  // == ECX
       ) ?[4]u32

New module: cpuid.zig (I can take it)
Comptime: returns host's results
Runtime: returns target's results

Related: #215, #767, #1018

[tuket]

https://en.wikipedia.org/wiki/CPUID
I like the idea

[daurnimator]

Comptime: returns host's results

There's nothing in zig (apart from @embedFile I guess) that exposes information about the host. Why would you want/need this?

[pixelherodev]

I agree; there is no practical benefit to that functionality, so it would just increase the compiler's complexity without providing any real benefits.

[ElementW]

This proposal has a couple issues in my opinion:

• This signature is very x86-y:
  • inputs & outputs are 32-bit, but some targets have other lengths for their cpuid equivalent; e.g. RISC-V CSRs are of the core's native bit length (XLEN), and it's not just left-padding with zeroes
  • not all architectures have dynamically selectable feature registers; e.g. ARM's mrs instructions encode the selected register in its instruction directly
  • archs may have more or less than 2 parameter registers/inputs
• It doesn't need to be a builtin really. Since how to get the CPU info and what you get back is very arch-specific you need to wrap that around code to discriminate the features you want, you'll need to either:
  • use said wrapper (possibly this could end up in the standard lib)
  • or roll your own, in which case having to call the target architecture's cpuid instruction equivalent by yourself will not make the task any harder
• Returning the host/target's results depending on comptime is nothing short of a recipe for making mistakes; the difference of action is invisible to somebody reading the source without knowing of your proposal's idiosyncrasies. At best you'd need to split it into @hostCpuid and @targetCpuid.
• As @daurnimator said, there's no reason to expose info about the host anyway, as you're producing code to be ran on a target, not the host. If you want the code to run on the host, then the target is the host.