fmt.Fprintln(&buf)
	fmt.Fprintf(&buf, "import \"runtime\"\n")
	fmt.Fprintln(&buf)
	fmt.Fprintf(&buf, "const defaultGO386 = `%s`\n", go386)
	fmt.Fprintf(&buf, "const defaultGOAMD64 = `%s`\n", goamd64)
	fmt.Fprintf(&buf, "const defaultGOARM = `%s`\n", goarm)
	fmt.Fprintf(&buf, "const defaultGOARM64 = `%s`\n", goarm64)
	fmt.Fprintf(&buf, "const defaultGOMIPS = `%s`\n", gomips)

	b = os.Getenv("GOARM64")
	if b == "" {
		b = "v8.0"
	}
	goarm64 = b

	b = os.Getenv("GO386")
	if b == "" {
		b = "sse2"
	}
	go386 = b

	b = os.Getenv("GOAMD64")
	if b == "" {
		b = "v1"
	}
	goamd64 = b

	b = os.Getenv("GOMIPS")
	if b == "" {
		b = "hardfloat"
	}
	gomips = b

	b = os.Getenv("GOMIPS64")
	if b == "" {
		b = "hardfloat"
	}
	gomips64 = b

//   - CGO_CXXFLAGS:  the effective CGO_CXXFLAGS environment variable
//   - CGO_LDFLAGS: the effective CGO_LDFLAGS environment variable
//   - GOARCH: the architecture target
//   - GOAMD64/GOARM/GO386/etc: the architecture feature level for GOARCH
//   - GOOS: the operating system target
//   - vcs: the version control system for the source tree where the build ran

	// match: (Ctz16NonZero x)
	// cond: buildcfg.GOAMD64 >= 3
	// result: (TZCNTL x)
	for {
		x := v_0
		if !(buildcfg.GOAMD64 >= 3) {
			break
		}
		v.reset(OpAMD64TZCNTL)
		v.AddArg(x)
		return true
	}
	// match: (Ctz16NonZero x)
	// cond: buildcfg.GOAMD64 < 3
	// result: (BSFL x)
	for {
		x := v_0
		if !(buildcfg.GOAMD64 < 3) {
			break
		}

	if cfg.Goarch == "386" {
		// Define GO386_value from cfg.GO386.
		args = append(args, "-D", "GO386_"+cfg.GO386)
	}

	if cfg.Goarch == "amd64" {
		// Define GOAMD64_value from cfg.GOAMD64.
		args = append(args, "-D", "GOAMD64_"+cfg.GOAMD64)
	}

	if cfg.Goarch == "mips" || cfg.Goarch == "mipsle" {
		// Define GOMIPS_value from cfg.GOMIPS.
		args = append(args, "-D", "GOMIPS_"+cfg.GOMIPS)
	}

For GOARCH=amd64, arm, ppc64, ppc64le, and riscv64, a particular feature level
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

		// 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
//

	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"},