// POPCNTx counts the number of set bits in the low-order (L=32,Q=64) bits of arg0.
		// POPCNTx instructions are only guaranteed to be available if GOAMD64>=v2.
		// For GOAMD64<v2, any use must be preceded by a successful runtime check of runtime.x86HasPOPCNT.
		{name: "POPCNTQ", argLength: 1, reg: gp11, asm: "POPCNTQ", clobberFlags: true},

// sets the feature build tags for all previous levels as well.
// For example, GOAMD64=v2 sets the amd64.v1 and amd64.v2 feature flags.
// This ensures that code making use of v2 features continues to compile
// when, say, GOAMD64=v4 is introduced.
// Code handling the absence of a particular feature level
// should use a negation:
//
//	//go:build !amd64.v2
//