[runtime/metrics](/pkg/runtime/metrics/) counter
named `/godebug/non-default-behavior/<name>:events`
that counts the number of times a particular program's
behavior has changed based on a non-default value
for that setting.
For example, when `GODEBUG=http2client=0` is set,
`/godebug/non-default-behavior/http2client:events`
counts the number of HTTP transports that the program
has configured without HTTP/2 support.

The set of pseudo-registers is the same for all architectures:
</p>

<ul>

<li>
<code>FP</code>: Frame pointer: arguments and locals.
</li>

<li>
<code>PC</code>: Program counter:
jumps and branches.
</li>

<li>
<code>SB</code>: Static base pointer: global symbols.
</li>

<li>
<code>SP</code>: Stack pointer: the highest address within the local stack frame.
</li>

// Repeat returns a new byte slice consisting of count copies of b.
//
// It panics if count is negative or if the result of (len(b) * count)
// overflows.
func Repeat(b []byte, count int) []byte {
	if count == 0 {
		return []byte{}
	}

	// Since we cannot return an error on overflow,
	// we should panic if the repeat will generate an overflow.
	// See golang.org/issue/16237.
	if count < 0 {

	for argNum := 0; ; argNum++ {
		tokens, tok := in.collectArgument(macro)
		args = append(args, tokens)
		if tok == ')' {
			break
		}
	}
	// Zero-argument macros are tricky.
	if len(macro.args) == 0 && len(args) == 1 && args[0] == nil {
		args = nil
	} else if len(args) != len(macro.args) {
		in.Error("wrong arg count for macro", macro.name)
	}

		if p.arch.Family == sys.ARM64 {
			if x >= 64 {
				p.errorf("register shift count too large: %s", str)
			}
			count = int16((x & 63) << 10)
		} else {
			if x >= 32 {
				p.errorf("register shift count too large: %s", str)
			}
			count = int16((x & 31) << 7)
		}
	default:
		p.errorf("unexpected %s in register shift", tok.String())
	}
	if p.arch.Family == sys.ARM64 {

	var rp *repeatedByte
	if len(r.buf) > 0 {
		rp = &r.buf[len(r.buf)-1]
		// Fast path, if p is entirely the same byte repeated.
		if lastByte := rp.b; len(p) > 0 && p[0] == lastByte {
			if bytes.Count(p, []byte{lastByte}) == len(p) {
				rp.n += int64(len(p))
				return len(p), nil
			}
		}
	}

	for _, b := range p {
		if rp == nil || rp.b != b {

	AMOMAXUD	X5, (X6), X7			// af3353e6
	AMOMINW		X5, (X6), X7			// af235386
	AMOMIND		X5, (X6), X7			// af335386
	AMOMINUW	X5, (X6), X7			// af2353c6
	AMOMINUD	X5, (X6), X7			// af3353c6

	// 10.1: Base Counters and Timers
	RDCYCLE		X5				// f32200c0
	RDTIME		X5				// f32210c0
	RDINSTRET	X5				// f32220c0

	// 11.5: Single-Precision Load and Store Instructions
	FLW	(X5), F0				// 07a00200
	FLW	4(X5), F0				// 07a04200