(discussed below).

When preparing any change that is permitted by Go 1 compatibility
but may nonetheless break some existing programs,
we first engineer the change to keep as many existing programs working as possible.
For the remaining programs,
we define a new GODEBUG setting that
allows individual programs to opt back in to the old behavior.
A GODEBUG setting may not be added if doing so is infeasible,

					return -1
				}
				i += o + 1
			}
			if s[i+1] == c1 && Equal(s[i:i+n], sep) {
				return i
			}
			fails++
			i++
			// Switch to bytealg.Index when IndexByte produces too many false positives.
			if fails > bytealg.Cutover(i) {
				r := bytealg.Index(s[i:], sep)
				if r >= 0 {
					return r + i
				}
				return -1
			}
		}
		return -1
	}
	c0 := sep[0]

		args = append([]interface{}{p.lex.File(), p.lineNum}, args...)
	}
	fmt.Fprintf(p.errorWriter, format, args...)
	p.errorCount++
	if p.errorCount > 10 && !*flags.AllErrors {
		log.Fatal("too many errors")
	}
}

func (p *Parser) pos() src.XPos {
	return p.ctxt.PosTable.XPos(src.MakePos(p.lex.Base(), uint(p.lineNum), 0))
}

func (p *Parser) Parse() (*obj.Prog, bool) {

// or any other common encoding).
func detectUTF8(s string) (valid, require bool) {
	for i := 0; i < len(s); {
		r, size := utf8.DecodeRuneInString(s[i:])
		i += size
		// Officially, ZIP uses CP-437, but many readers use the system's
		// local character encoding. Most encoding are compatible with a large
		// subset of CP-437, which itself is ASCII-like.
		//
		// Forbid 0x7e and 0x5c since EUC-KR and Shift-JIS replace those

func NewReader(r io.Reader) *Reader {
	return &Reader{r: r, curr: &regFileReader{r, 0}}
}

// Next advances to the next entry in the tar archive.
// The Header.Size determines how many bytes can be read for the next file.
// Any remaining data in the current file is automatically discarded.
// At the end of the archive, Next returns the error io.EOF.
//

// to avoid misleading negative results.
// This makes all the references to os.FileInfo in go1.txt
// be read as if they said fs.FileInfo, since os.FileInfo is now an alias.
// If there are many of these, we could do a more general solution,
// but for now the replacer is fine.
var aliasReplacer = strings.NewReplacer(
	"os.FileInfo", "fs.FileInfo",
	"os.FileMode", "fs.FileMode",
	"os.PathError", "fs.PathError",

<pre>
i := *p
if i &lt; 0 || i &gt;= len(funcs) {
	panic("invalid function index")
}
... complex code ...
// compiler must NOT reload i = *p here
funcs[i]()
</pre>

<p>
If the complex code needs many registers, a compiler for single-threaded programs
could discard <code>i</code> without saving a copy and then reload
<code>i = *p</code> just before
<code>funcs[i]()</code>.