func doinit() {
	options = []option{
		{Name: "adx", Feature: &X86.HasADX},
		{Name: "aes", Feature: &X86.HasAES},
		{Name: "erms", Feature: &X86.HasERMS},
		{Name: "pclmulqdq", Feature: &X86.HasPCLMULQDQ},
		{Name: "rdtscp", Feature: &X86.HasRDTSCP},
		{Name: "sha", Feature: &X86.HasSHA},
	}
	level := getGOAMD64level()
	if level < 2 {
		// These options are required at level 2. At lower levels
		// they can be turned off.

		ICEBP, INSB, INSD, INSW, INT, INTO, INVD, IRET, IRETQ,
		LAHF, LEAVE, LRET, MONITOR, MWAIT, NOP, OUTSB, OUTSD, OUTSW,
		PAUSE, POPA, POPF, POPFQ, PUSHA, PUSHF, PUSHFQ,
		RDMSR, RDPMC, RDTSC, RDTSCP, RET, RSM,
		SAHF, STC, STD, STI, SYSENTER, SYSEXIT, SYSRET,
		UD2, WBINVD, WRMSR, XEND, XLATB, XTEST:

		if inst.Op == NOP && inst.Opcode>>24 != 0x90 {
			break
		}

	"RDFSBASEQ",
	"RDGSBASEL",
	"RDGSBASEQ",
	"RDMSR",
	"RDPID",
	"RDPKRU",
	"RDPMC",
	"RDRANDL",
	"RDRANDQ",
	"RDRANDW",
	"RDSEEDL",
	"RDSEEDQ",
	"RDSEEDW",
	"RDTSC",
	"RDTSCP",
	"REP",
	"REPN",
	"RETFL",
	"RETFQ",
	"RETFW",
	"ROLB",
	"ROLL",
	"ROLQ",
	"ROLW",
	"RORB",
	"RORL",
	"RORQ",
	"RORW",
	"RORXL",
	"RORXQ",
	"ROUNDPD",

	for _, key := range keys {
		m[key] = true
	}
	return m
}

var runtimeFeatures = setOf(
	"adx", "aes", "avx", "avx2", "bmi1", "bmi2", "erms", "fma",
	"pclmulqdq", "popcnt", "rdtscp", "sse3", "sse41", "sse42", "ssse3",
)

var featureToOpcodes = map[string][]string{
	// Note: we include *q, *l, and plain opcodes here.
	// go tool objdump doesn't include a [QL] on popcnt instructions, until CL 351889

	JMP	rdtsc  // no fence instructions available
#endif
	CMPB	internal∕cpu·X86+const_offsetX86HasRDTSCP(SB), $1
	JNE	fences
	// Instruction stream serializing RDTSCP is supported.
	// RDTSCP is supported by Intel Nehalem (2008) and
	// AMD K8 Rev. F (2006) and newer.
	RDTSCP
done:
	MOVL	AX, ret_lo+0(FP)
	MOVL	DX, ret_hi+4(FP)
	RET
fences:
	// MFENCE is instruction stream serializing and flushes the

TEXT runtime·cputicks(SB),NOSPLIT,$0-0
	CMPB	internal∕cpu·X86+const_offsetX86HasRDTSCP(SB), $1
	JNE	fences
	// Instruction stream serializing RDTSCP is supported.
	// RDTSCP is supported by Intel Nehalem (2008) and
	// AMD K8 Rev. F (2006) and newer.
	RDTSCP
done:
	SHLQ	$32, DX
	ADDQ	DX, AX
	MOVQ	AX, ret+0(FP)
	RET
fences:
	// MFENCE is instruction stream serializing and flushes the

	RCR:             "RCR",
	RDFSBASE:        "RDFSBASE",
	RDGSBASE:        "RDGSBASE",
	RDMSR:           "RDMSR",
	RDPMC:           "RDPMC",
	RDRAND:          "RDRAND",
	RDTSC:           "RDTSC",
	RDTSCP:          "RDTSCP",
	RET:             "RET",
	ROL:             "ROL",
	ROR:             "ROR",
	ROUNDPD:         "ROUNDPD",
	ROUNDPS:         "ROUNDPS",
	ROUNDSD:         "ROUNDSD",
	ROUNDSS:         "ROUNDSS",

	RDSEEDL R11                             // 410fc7fb
	RDSEEDQ DX                              // 480fc7fa
	RDSEEDQ R11                             // 490fc7fb
	RDTSC                                   // 0f31
	RDTSCP                                  // 0f01f9
	JCS 2(PC)
	//TODO: RETQ                            // c3
	JCS 2(PC)
	//TODO: RETQ $0xf123                    // c223f1
	JCS 2(PC)