for i := 0; i < 5<<10; i++ {
		b.Write(buf)
		b.Read(buf)
		if i == 0 {
			cap0 = b.Cap()
		}
	}
	cap1 := b.Cap()
	// (*Buffer).grow allows for 2x capacity slop before sliding,
	// so set our error threshold at 3x.
	if cap1 > cap0*3 {
		t.Errorf("buffer cap = %d; too big (grew from %d)", cap1, cap0)
	}
}

func BenchmarkWriteByte(b *testing.B) {
	const n = 4 << 10
	b.SetBytes(n)

	// ppc64x:-"MOVBZ\tR\\d+,\\sR\\d+"
	val64[0] = uint64(*u8)

	// ppc64x:-"MOVHZ\tR\\d+,\\sR\\d+"
	val64[1] = uint64(*u16)

	// ppc64x:-"MOVWZ\tR\\d+,\\sR\\d+"
	val64[2] = uint64(*u32)
}

func cmp16(u8 *uint8, x32 *int32, u32 *uint32, x64 *int64, u64 *uint64) bool {

	// ppc64x:-"MOVBZ\tR\\d+,\\sR\\d+"
	if uint16(*u8) == val16[0] {
		return true
	}

	// ppc64x:-"MOVHZ\tR\\d+,\\sR\\d+"

		{name: "CMPL", argLength: 2, reg: gp2flags, asm: "CMPL", typ: "Flags"},                    // arg0 compare to arg1
		{name: "CMPW", argLength: 2, reg: gp2flags, asm: "CMPW", typ: "Flags"},                    // arg0 compare to arg1
		{name: "CMPB", argLength: 2, reg: gp2flags, asm: "CMPB", typ: "Flags"},                    // arg0 compare to arg1

		for x := 0; x <= size-n; x = x*7 + 1 { // offset in src
			for y := 0; y <= size-n; y = y*9 + 1 { // offset in dst
				copy(dst[y:y+n], src[x:x+n])
				copyref(ref[y:y+n], src[x:x+n])
				p := cmpb(dst, ref)
				if p >= 0 {
					t.Fatalf("Copy failed, copying from src[%d:%d] to dst[%d:%d].\nOffset %d is different, %v != %v", x, x+n, y, y+n, p, dst[p], ref[p])
				}
			}
		}
	}
}

//go:build !purego

// func addMulVVW1024(z *uint, x *uint, y uint) (c uint)
// Requires: ADX, BMI2
TEXT ·addMulVVW1024(SB), $0-32
	CMPB ·supportADX+0(SB), $0x01
	JEQ  adx
	MOVQ z+0(FP), CX
	MOVQ x+8(FP), BX
	MOVQ y+16(FP), SI
	XORQ DI, DI

	// Iteration 0
	MOVQ (BX), AX
	MULQ SI
	ADDQ (CX), AX
	ADCQ $0x00, DX
	ADDQ DI, AX

	"jmp",
	"callq",
	"cmpb",
}

var i386GnuNeed = []string{
	"jmp",
	"call",
	"cmp",
}

var armNeed = []string{
	"B main.main(SB)",
	"BL main.Println(SB)",
	"RET",
}

var arm64Need = []string{
	"JMP main.main(SB)",
	"CALL main.Println(SB)",
	"RET",
}

var armGnuNeed = []string{ // for both ARM and AMR64
	"ldr",
	"bl",
	"cmp",
}

var ppcNeed = []string{

	MOVL	$1, 0(SP)
	CALL	runtime·exit(SB)
	CALL	runtime·abort(SB)

has_cpuid:
	MOVL	$0, AX
	CPUID
	MOVL	AX, SI
	CMPL	AX, $0
	JE	nocpuinfo

	CMPL	BX, $0x756E6547  // "Genu"
	JNE	notintel
	CMPL	DX, $0x49656E69  // "ineI"
	JNE	notintel
	CMPL	CX, $0x6C65746E  // "ntel"
	JNE	notintel
	MOVB	$1, runtime·isIntel(SB)
notintel:

	// Load EAX=1 cpuid flags
	MOVL	$1, AX
	CPUID

		// CMPx: compare arg0 to arg1.
		{name: "CMPQ", argLength: 2, reg: gp2flags, asm: "CMPQ", typ: "Flags"},
		{name: "CMPL", argLength: 2, reg: gp2flags, asm: "CMPL", typ: "Flags"},
		{name: "CMPW", argLength: 2, reg: gp2flags, asm: "CMPW", typ: "Flags"},
		{name: "CMPB", argLength: 2, reg: gp2flags, asm: "CMPB", typ: "Flags"},

		// CMPxconst: compare arg0 to auxint.

	v_2 := v.Args[2]
	v_1 := v.Args[1]
	v_0 := v.Args[0]
	b := v.Block
	typ := &b.Func.Config.Types
	// match: (CMPBload {sym} [off] ptr x mem)
	// result: (CMPB (MOVBload {sym} [off] ptr mem) x)
	for {
		off := auxIntToInt32(v.AuxInt)
		sym := auxToSym(v.Aux)
		ptr := v_0
		x := v_1
		mem := v_2
		v.reset(OpAMD64CMPB)

	v := reflect.ValueOf(x)
	return v.Len()
}

func len5(x chan int) int { // ERROR "x does not escape"
	v := reflect.ValueOf(x)
	return v.Len()
}

func cap1(x []int) int { // ERROR "x does not escape"
	v := reflect.ValueOf(x) // ERROR "x does not escape"
	return v.Cap()
}

func cap2(x [3]int) int {
	v := reflect.ValueOf(x) // ERROR "x does not escape"