// 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
//

	MOVQ	CX, g(BX)
	LEAQ	runtime·m0(SB), AX

	// save m->g0 = g0
	MOVQ	CX, m_g0(AX)
	// save m0 to g0->m
	MOVQ	AX, g_m(CX)

	CLD				// convention is D is always left cleared

	// Check GOAMD64 requirements
	// We need to do this after setting up TLS, so that
	// we can report an error if there is a failure. See issue 49586.
#ifdef NEED_FEATURES_CX
	MOVL	$0, AX
	CPUID
	CMPL	AX, $0
	JE	bad_cpu

	// value[0] is the variant-changing environment variable, and values[1:]
	// are the supported variants.
	archVariants = map[string][]string{
		"386":     {"GO386", "sse2", "softfloat"},
		"amd64":   {"GOAMD64", "v1", "v2", "v3", "v4"},
		"arm":     {"GOARM", "5", "6", "7", "7,softfloat"},
		"arm64":   {"GOARM64", "v8.0", "v8.1"},
		"loong64": {},
		"mips":    {"GOMIPS", "hardfloat", "softfloat"},

			if !s.config.UseFMA {
				s.vars[n] = s.callResult(n, callNormal) // types.Types[TFLOAT64]
				return s.variable(n, types.Types[types.TFLOAT64])
			}

			if buildcfg.GOAMD64 >= 3 {
				return s.newValue3(ssa.OpFMA, types.Types[types.TFLOAT64], args[0], args[1], args[2])
			}

			v := s.entryNewValue0A(ssa.OpHasCPUFeature, types.Types[types.TBOOL], ir.Syms.X86HasFMA)
			b := s.endBlock()