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.

	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