osSupportsAVX := false
	osSupportsAVX512 := false
	// For XGETBV, OSXSAVE bit is required and sufficient.
	if X86.HasOSXSAVE {
		eax, _ := xgetbv()
		// Check if XMM and YMM registers have OS support.
		osSupportsAVX = isSet(eax, 1<<1) && isSet(eax, 1<<2)

		// AVX512 detection does not work on Darwin,
		// see https://github.com/golang/go/issues/49233
		//

	}
	if k := ft.OutSlice()[0].Kind_ & abi.KindMask; k == abi.Float32 || k == abi.Float64 {
		// In cdecl and stdcall, float results are returned in
		// ST(0). In fastcall, they're returned in XMM0.
		// Either way, it's not AX.
		panic("compileCallback: float results not supported")
	}
	if intArgRegs == 0 {
		// Make room for the uintptr-sized result.
		// If there are argument registers, the return value will

	Pq   = 0xff // both escapes: 66 0f
	Pb   = 0xfe // byte operands
	Pf2  = 0xf2 // xmm escape 1: f2 0f
	Pf3  = 0xf3 // xmm escape 2: f3 0f
	Pef3 = 0xf5 // xmm escape 2 with 16-bit prefix: 66 f3 0f
	Pq3  = 0x67 // xmm escape 3: 66 48 0f
	Pq4  = 0x68 // xmm escape 4: 66 0F 38
	Pq4w = 0x69 // Pq4 with Rex.w 66 0F 38
	Pq5  = 0x6a // xmm escape 5: F3 0F 38
	Pq5w = 0x6b // Pq5 with Rex.w F3 0F 38

#define V3_EXT_FEATURES_CX (V2_EXT_FEATURES_CX | 1 << 5)
                         // BMI1     AVX2     BMI2
#define V3_EXT_FEATURES_BX (1 << 3 | 1 << 5 | 1 << 8)
                       // XMM      YMM
#define V3_OS_SUPPORT_AX (1 << 1 | 1 << 2)

#define V4_FEATURES_CX V3_FEATURES_CX

#define V4_EXT_FEATURES_CX V3_EXT_FEATURES_CX