Why use `klauspost/cpuid` rather than `x/sys/cpu` for avx2 and sse4 detection?

[coolaj86]

I see that the github.com/klauspost/cpuid is being used for avx2 and sse4 detection here:

blake3/internal/consts/cpu.go

Lines 12 to 18 in 50f20c8

	HasAVX2 = cpuid.CPU.Has(cpuid.AVX2) &&
	os.Getenv("BLAKE3_DISABLE_AVX2") == "" &&
	os.Getenv("BLAKE3_PUREGO") == ""
	HasSSE41 = cpuid.CPU.Has(cpuid.SSE4) &&
	os.Getenv("BLAKE3_DISABLE_SSE41") == "" &&
	os.Getenv("BLAKE3_PUREGO") == ""

Is there any particular reason to not use the Go team's implementation?
https://pkg.go.dev/golang.org/x/sys/cpu

[zeebo]

I don't know. Why do you ask?

[coolaj86]

I was doing a supply chain audit of dependencies in one of the projects I'm working on and I thought it was odd that cpuid was being included.

I traced it back to blake3 and then found that it's being used somewhat "off-label" for generic CPU feature detection, and I figured that's the sort of thing that would be in Go's stdlib, which it turns out to be.