libgo, compiler: Upgrade libgo to Go 1.4, except for runtime.

This upgrades all of libgo other than the runtime package to
the Go 1.4 release.  In Go 1.4 much of the runtime was
rewritten into Go.  Merging that code will take more time and
will not change the API, so I'm putting it off for now.

There are a few runtime changes anyhow, to accomodate other
packages that rely on minor modifications to the runtime
support.

The compiler changes slightly to add a one-bit flag to each
type descriptor kind that is stored directly in an interface,
which for gccgo is currently only pointer types.  Another
one-bit flag (gcprog) is reserved because it is used by the gc
compiler, but gccgo does not currently use it.

There is another error check in the compiler since I ran
across it during testing.

gotools/:
	* Makefile.am (go_cmd_go_files): Sort entries.  Add generate.go.
	* Makefile.in: Rebuild.

From-SVN: r219627

5 files changed, 197 insertions, 97 deletions

diff --git a/libgo/go/strconv/atoi.go b/libgo/go/strconv/atoi.go
index cbf0380..9ecec5a 100644
--- a/libgo/go/strconv/atoi.go
+++ b/libgo/go/strconv/atoi.go
@@ -31,7 +31,7 @@ func rangeError(fn, str string) *NumError {
 	return &NumError{fn, str, ErrRange}
 }
 
-const intSize = 32 << uint(^uint(0)>>63)
+const intSize = 32 << (^uint(0) >> 63)
 
 // IntSize is the size in bits of an int or uint value.
 const IntSize = intSize
diff --git a/libgo/go/strconv/isprint.go b/libgo/go/strconv/isprint.go
index 91f1795..80738ed 100644
--- a/libgo/go/strconv/isprint.go
+++ b/libgo/go/strconv/isprint.go
@@ -3,20 +3,19 @@
 // license that can be found in the LICENSE file.
 
 // DO NOT EDIT.  GENERATED BY
-//     go run makeisprint.go >x && mv x isprint.go
+//     go run makeisprint.go -output isprint.go
 
 package strconv
 
-// (470+136+60)*2 + (218)*4 = 2204 bytes
+// (468+138+67)*2 + (326)*4 = 2650 bytes
 
 var isPrint16 = []uint16{
 	0x0020, 0x007e,
 	0x00a1, 0x0377,
-	0x037a, 0x037e,
-	0x0384, 0x0527,
-	0x0531, 0x0556,
+	0x037a, 0x037f,
+	0x0384, 0x0556,
 	0x0559, 0x058a,
-	0x058f, 0x05c7,
+	0x058d, 0x05c7,
 	0x05d0, 0x05ea,
 	0x05f0, 0x05f4,
 	0x0606, 0x061b,
@@ -27,7 +26,7 @@ var isPrint16 = []uint16{
 	0x0800, 0x082d,
 	0x0830, 0x085b,
 	0x085e, 0x085e,
-	0x08a0, 0x08ac,
+	0x08a0, 0x08b2,
 	0x08e4, 0x098c,
 	0x098f, 0x0990,
 	0x0993, 0x09b2,
@@ -72,18 +71,17 @@ var isPrint16 = []uint16{
 	0x0bd0, 0x0bd0,
 	0x0bd7, 0x0bd7,
 	0x0be6, 0x0bfa,
-	0x0c01, 0x0c39,
+	0x0c00, 0x0c39,
 	0x0c3d, 0x0c4d,
 	0x0c55, 0x0c59,
 	0x0c60, 0x0c63,
 	0x0c66, 0x0c6f,
-	0x0c78, 0x0c7f,
-	0x0c82, 0x0cb9,
+	0x0c78, 0x0cb9,
 	0x0cbc, 0x0ccd,
 	0x0cd5, 0x0cd6,
 	0x0cde, 0x0ce3,
 	0x0ce6, 0x0cf2,
-	0x0d02, 0x0d3a,
+	0x0d01, 0x0d3a,
 	0x0d3d, 0x0d4e,
 	0x0d57, 0x0d57,
 	0x0d60, 0x0d63,
@@ -94,6 +92,7 @@ var isPrint16 = []uint16{
 	0x0dc0, 0x0dc6,
 	0x0dca, 0x0dca,
 	0x0dcf, 0x0ddf,
+	0x0de6, 0x0def,
 	0x0df2, 0x0df4,
 	0x0e01, 0x0e3a,
 	0x0e3f, 0x0e5b,
@@ -120,7 +119,7 @@ var isPrint16 = []uint16{
 	0x1380, 0x1399,
 	0x13a0, 0x13f4,
 	0x1400, 0x169c,
-	0x16a0, 0x16f0,
+	0x16a0, 0x16f8,
 	0x1700, 0x1714,
 	0x1720, 0x1736,
 	0x1740, 0x1753,
@@ -133,8 +132,7 @@ var isPrint16 = []uint16{
 	0x1820, 0x1877,
 	0x1880, 0x18aa,
 	0x18b0, 0x18f5,
-	0x1900, 0x191c,
-	0x1920, 0x192b,
+	0x1900, 0x192b,
 	0x1930, 0x193b,
 	0x1940, 0x1940,
 	0x1944, 0x196d,
@@ -147,6 +145,7 @@ var isPrint16 = []uint16{
 	0x1a7f, 0x1a89,
 	0x1a90, 0x1a99,
 	0x1aa0, 0x1aad,
+	0x1ab0, 0x1abe,
 	0x1b00, 0x1b4b,
 	0x1b50, 0x1b7c,
 	0x1b80, 0x1bf3,
@@ -154,8 +153,8 @@ var isPrint16 = []uint16{
 	0x1c3b, 0x1c49,
 	0x1c4d, 0x1c7f,
 	0x1cc0, 0x1cc7,
-	0x1cd0, 0x1cf6,
-	0x1d00, 0x1de6,
+	0x1cd0, 0x1cf9,
+	0x1d00, 0x1df5,
 	0x1dfc, 0x1f15,
 	0x1f18, 0x1f1d,
 	0x1f20, 0x1f45,
@@ -168,21 +167,23 @@ var isPrint16 = []uint16{
 	0x2030, 0x205e,
 	0x2070, 0x2071,
 	0x2074, 0x209c,
-	0x20a0, 0x20ba,
+	0x20a0, 0x20bd,
 	0x20d0, 0x20f0,
 	0x2100, 0x2189,
-	0x2190, 0x23f3,
+	0x2190, 0x23fa,
 	0x2400, 0x2426,
 	0x2440, 0x244a,
-	0x2460, 0x2b4c,
-	0x2b50, 0x2b59,
+	0x2460, 0x2b73,
+	0x2b76, 0x2b95,
+	0x2b98, 0x2bb9,
+	0x2bbd, 0x2bd1,
 	0x2c00, 0x2cf3,
 	0x2cf9, 0x2d27,
 	0x2d2d, 0x2d2d,
 	0x2d30, 0x2d67,
 	0x2d6f, 0x2d70,
 	0x2d7f, 0x2d96,
-	0x2da0, 0x2e3b,
+	0x2da0, 0x2e42,
 	0x2e80, 0x2ef3,
 	0x2f00, 0x2fd5,
 	0x2ff0, 0x2ffb,
@@ -196,11 +197,10 @@ var isPrint16 = []uint16{
 	0xa000, 0xa48c,
 	0xa490, 0xa4c6,
 	0xa4d0, 0xa62b,
-	0xa640, 0xa697,
-	0xa69f, 0xa6f7,
-	0xa700, 0xa793,
-	0xa7a0, 0xa7aa,
-	0xa7f8, 0xa82b,
+	0xa640, 0xa6f7,
+	0xa700, 0xa7ad,
+	0xa7b0, 0xa7b1,
+	0xa7f7, 0xa82b,
 	0xa830, 0xa839,
 	0xa840, 0xa877,
 	0xa880, 0xa8c4,
@@ -209,17 +209,16 @@ var isPrint16 = []uint16{
 	0xa900, 0xa953,
 	0xa95f, 0xa97c,
 	0xa980, 0xa9d9,
-	0xa9de, 0xa9df,
-	0xaa00, 0xaa36,
+	0xa9de, 0xaa36,
 	0xaa40, 0xaa4d,
 	0xaa50, 0xaa59,
-	0xaa5c, 0xaa7b,
-	0xaa80, 0xaac2,
+	0xaa5c, 0xaac2,
 	0xaadb, 0xaaf6,
 	0xab01, 0xab06,
 	0xab09, 0xab0e,
 	0xab11, 0xab16,
-	0xab20, 0xab2e,
+	0xab20, 0xab5f,
+	0xab64, 0xab65,
 	0xabc0, 0xabed,
 	0xabf0, 0xabf9,
 	0xac00, 0xd7a3,
@@ -235,7 +234,7 @@ var isPrint16 = []uint16{
 	0xfd92, 0xfdc7,
 	0xfdf0, 0xfdfd,
 	0xfe00, 0xfe19,
-	0xfe20, 0xfe26,
+	0xfe20, 0xfe2d,
 	0xfe30, 0xfe6b,
 	0xfe70, 0xfefc,
 	0xff01, 0xffbe,
@@ -252,15 +251,12 @@ var isNotPrint16 = []uint16{
 	0x038b,
 	0x038d,
 	0x03a2,
+	0x0530,
 	0x0560,
 	0x0588,
 	0x0590,
 	0x06dd,
 	0x083f,
-	0x08a1,
-	0x08ff,
-	0x0978,
-	0x0980,
 	0x0984,
 	0x09a9,
 	0x09b1,
@@ -294,10 +290,10 @@ var isNotPrint16 = []uint16{
 	0x0c0d,
 	0x0c11,
 	0x0c29,
-	0x0c34,
 	0x0c45,
 	0x0c49,
 	0x0c57,
+	0x0c80,
 	0x0c84,
 	0x0c8d,
 	0x0c91,
@@ -345,7 +341,9 @@ var isNotPrint16 = []uint16{
 	0x170d,
 	0x176d,
 	0x1771,
+	0x191f,
 	0x1a5f,
+	0x1cf7,
 	0x1f58,
 	0x1f5a,
 	0x1f5c,
@@ -355,7 +353,7 @@ var isNotPrint16 = []uint16{
 	0x1fdc,
 	0x1ff5,
 	0x208f,
-	0x2700,
+	0x2bc9,
 	0x2c2f,
 	0x2c5f,
 	0x2d26,
@@ -372,9 +370,12 @@ var isNotPrint16 = []uint16{
 	0x318f,
 	0x321f,
 	0x32ff,
+	0xa69e,
 	0xa78f,
 	0xa9ce,
+	0xa9ff,
 	0xab27,
+	0xab2f,
 	0xfb37,
 	0xfb3d,
 	0xfb3f,
@@ -392,21 +393,31 @@ var isPrint32 = []uint32{
 	0x010080, 0x0100fa,
 	0x010100, 0x010102,
 	0x010107, 0x010133,
-	0x010137, 0x01018a,
+	0x010137, 0x01018c,
 	0x010190, 0x01019b,
+	0x0101a0, 0x0101a0,
 	0x0101d0, 0x0101fd,
 	0x010280, 0x01029c,
 	0x0102a0, 0x0102d0,
+	0x0102e0, 0x0102fb,
 	0x010300, 0x010323,
 	0x010330, 0x01034a,
+	0x010350, 0x01037a,
 	0x010380, 0x0103c3,
 	0x0103c8, 0x0103d5,
 	0x010400, 0x01049d,
 	0x0104a0, 0x0104a9,
+	0x010500, 0x010527,
+	0x010530, 0x010563,
+	0x01056f, 0x01056f,
+	0x010600, 0x010736,
+	0x010740, 0x010755,
+	0x010760, 0x010767,
 	0x010800, 0x010805,
 	0x010808, 0x010838,
 	0x01083c, 0x01083c,
-	0x01083f, 0x01085f,
+	0x01083f, 0x01089e,
+	0x0108a7, 0x0108af,
 	0x010900, 0x01091b,
 	0x01091f, 0x010939,
 	0x01093f, 0x01093f,
@@ -417,32 +428,72 @@ var isPrint32 = []uint32{
 	0x010a38, 0x010a3a,
 	0x010a3f, 0x010a47,
 	0x010a50, 0x010a58,
-	0x010a60, 0x010a7f,
+	0x010a60, 0x010a9f,
+	0x010ac0, 0x010ae6,
+	0x010aeb, 0x010af6,
 	0x010b00, 0x010b35,
 	0x010b39, 0x010b55,
 	0x010b58, 0x010b72,
-	0x010b78, 0x010b7f,
+	0x010b78, 0x010b91,
+	0x010b99, 0x010b9c,
+	0x010ba9, 0x010baf,
 	0x010c00, 0x010c48,
 	0x010e60, 0x010e7e,
 	0x011000, 0x01104d,
 	0x011052, 0x01106f,
-	0x011080, 0x0110c1,
+	0x01107f, 0x0110c1,
 	0x0110d0, 0x0110e8,
 	0x0110f0, 0x0110f9,
 	0x011100, 0x011143,
+	0x011150, 0x011176,
 	0x011180, 0x0111c8,
-	0x0111d0, 0x0111d9,
+	0x0111cd, 0x0111cd,
+	0x0111d0, 0x0111da,
+	0x0111e1, 0x0111f4,
+	0x011200, 0x01123d,
+	0x0112b0, 0x0112ea,
+	0x0112f0, 0x0112f9,
+	0x011301, 0x01130c,
+	0x01130f, 0x011310,
+	0x011313, 0x011339,
+	0x01133c, 0x011344,
+	0x011347, 0x011348,
+	0x01134b, 0x01134d,
+	0x011357, 0x011357,
+	0x01135d, 0x011363,
+	0x011366, 0x01136c,
+	0x011370, 0x011374,
+	0x011480, 0x0114c7,
+	0x0114d0, 0x0114d9,
+	0x011580, 0x0115b5,
+	0x0115b8, 0x0115c9,
+	0x011600, 0x011644,
+	0x011650, 0x011659,
 	0x011680, 0x0116b7,
 	0x0116c0, 0x0116c9,
-	0x012000, 0x01236e,
-	0x012400, 0x012462,
-	0x012470, 0x012473,
+	0x0118a0, 0x0118f2,
+	0x0118ff, 0x0118ff,
+	0x011ac0, 0x011af8,
+	0x012000, 0x012398,
+	0x012400, 0x012474,
 	0x013000, 0x01342e,
 	0x016800, 0x016a38,
+	0x016a40, 0x016a69,
+	0x016a6e, 0x016a6f,
+	0x016ad0, 0x016aed,
+	0x016af0, 0x016af5,
+	0x016b00, 0x016b45,
+	0x016b50, 0x016b77,
+	0x016b7d, 0x016b8f,
 	0x016f00, 0x016f44,
 	0x016f50, 0x016f7e,
 	0x016f8f, 0x016f9f,
 	0x01b000, 0x01b001,
+	0x01bc00, 0x01bc6a,
+	0x01bc70, 0x01bc7c,
+	0x01bc80, 0x01bc88,
+	0x01bc90, 0x01bc99,
+	0x01bc9c, 0x01bc9f,
 	0x01d000, 0x01d0f5,
 	0x01d100, 0x01d126,
 	0x01d129, 0x01d172,
@@ -458,6 +509,8 @@ var isPrint32 = []uint32{
 	0x01d54a, 0x01d6a5,
 	0x01d6a8, 0x01d7cb,
 	0x01d7ce, 0x01d7ff,
+	0x01e800, 0x01e8c4,
+	0x01e8c7, 0x01e8d6,
 	0x01ee00, 0x01ee24,
 	0x01ee27, 0x01ee3b,
 	0x01ee42, 0x01ee42,
@@ -469,28 +522,30 @@ var isPrint32 = []uint32{
 	0x01f000, 0x01f02b,
 	0x01f030, 0x01f093,
 	0x01f0a0, 0x01f0ae,
-	0x01f0b1, 0x01f0be,
-	0x01f0c1, 0x01f0df,
-	0x01f100, 0x01f10a,
+	0x01f0b1, 0x01f0f5,
+	0x01f100, 0x01f10c,
 	0x01f110, 0x01f16b,
 	0x01f170, 0x01f19a,
 	0x01f1e6, 0x01f202,
 	0x01f210, 0x01f23a,
 	0x01f240, 0x01f248,
 	0x01f250, 0x01f251,
-	0x01f300, 0x01f320,
-	0x01f330, 0x01f37c,
-	0x01f380, 0x01f393,
-	0x01f3a0, 0x01f3ca,
-	0x01f3e0, 0x01f3f0,
-	0x01f400, 0x01f4fc,
-	0x01f500, 0x01f53d,
-	0x01f540, 0x01f543,
-	0x01f550, 0x01f567,
-	0x01f5fb, 0x01f640,
-	0x01f645, 0x01f64f,
-	0x01f680, 0x01f6c5,
+	0x01f300, 0x01f32c,
+	0x01f330, 0x01f37d,
+	0x01f380, 0x01f3ce,
+	0x01f3d4, 0x01f3f7,
+	0x01f400, 0x01f54a,
+	0x01f550, 0x01f642,
+	0x01f645, 0x01f6cf,
+	0x01f6e0, 0x01f6ec,
+	0x01f6f0, 0x01f6f3,
 	0x01f700, 0x01f773,
+	0x01f780, 0x01f7d4,
+	0x01f800, 0x01f80b,
+	0x01f810, 0x01f847,
+	0x01f850, 0x01f859,
+	0x01f860, 0x01f887,
+	0x01f890, 0x01f8ad,
 	0x020000, 0x02a6d6,
 	0x02a700, 0x02b734,
 	0x02b740, 0x02b81d,
@@ -503,7 +558,6 @@ var isNotPrint32 = []uint16{ // add 0x10000 to each entry
 	0x0027,
 	0x003b,
 	0x003e,
-	0x031f,
 	0x039e,
 	0x0809,
 	0x0836,
@@ -513,6 +567,15 @@ var isNotPrint32 = []uint16{ // add 0x10000 to each entry
 	0x0a18,
 	0x10bd,
 	0x1135,
+	0x1212,
+	0x1304,
+	0x1329,
+	0x1331,
+	0x1334,
+	0x246f,
+	0x6a5f,
+	0x6b5a,
+	0x6b62,
 	0xd455,
 	0xd49d,
 	0xd4ad,
@@ -552,11 +615,10 @@ var isNotPrint32 = []uint16{ // add 0x10000 to each entry
 	0xee8a,
 	0xeea4,
 	0xeeaa,
+	0xf0c0,
 	0xf0d0,
 	0xf12f,
-	0xf336,
-	0xf3c5,
-	0xf43f,
-	0xf441,
-	0xf4f8,
+	0xf4ff,
+	0xf57a,
+	0xf5a4,
 }
diff --git a/libgo/go/strconv/makeisprint.go b/libgo/go/strconv/makeisprint.go
index 216159c..588d0a0 100644
--- a/libgo/go/strconv/makeisprint.go
+++ b/libgo/go/strconv/makeisprint.go
@@ -4,15 +4,26 @@
 
 // +build ignore
 
-// makeisprint generates the tables for strconv's compact isPrint.
+//
+// usage:
+//
+// go run makeisprint.go -output isprint.go
+//
+
 package main
 
 import (
+	"bytes"
+	"flag"
 	"fmt"
-	"os"
+	"go/format"
+	"io/ioutil"
+	"log"
 	"unicode"
 )
 
+var filename = flag.String("output", "isprint.go", "output file name")
+
 var (
 	range16  []uint16
 	except16 []uint16
@@ -110,6 +121,8 @@ func to16(x []uint32) []uint16 {
 }
 
 func main() {
+	flag.Parse()
+
 	rang, except := scan(0, 0xFFFF)
 	range16 = to16(rang)
 	except16 = to16(except)
@@ -117,49 +130,58 @@ func main() {
 
 	for i := rune(0); i <= unicode.MaxRune; i++ {
 		if isPrint(i) != unicode.IsPrint(i) {
-			fmt.Fprintf(os.Stderr, "%U: isPrint=%v, want %v\n", i, isPrint(i), unicode.IsPrint(i))
-			return
+			log.Fatalf("%U: isPrint=%v, want %v\n", i, isPrint(i), unicode.IsPrint(i))
 		}
 	}
 
-	fmt.Printf(`// Copyright 2013 The Go Authors. All rights reserved.
+	var buf bytes.Buffer
+
+	fmt.Fprintf(&buf, `// Copyright 2013 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.` + "\n\n")
-	fmt.Printf("// DO NOT EDIT.  GENERATED BY\n")
-	fmt.Printf("//     go run makeisprint.go >x && mv x isprint.go\n\n")
-	fmt.Printf("package strconv\n\n")
+// license that can be found in the LICENSE file.`+"\n\n")
+	fmt.Fprintf(&buf, "// DO NOT EDIT.  GENERATED BY\n")
+	fmt.Fprintf(&buf, "//     go run makeisprint.go -output isprint.go\n\n")
+	fmt.Fprintf(&buf, "package strconv\n\n")
 
-	fmt.Printf("// (%d+%d+%d)*2 + (%d)*4 = %d bytes\n\n",
+	fmt.Fprintf(&buf, "// (%d+%d+%d)*2 + (%d)*4 = %d bytes\n\n",
 		len(range16), len(except16), len(except32),
 		len(range32),
 		(len(range16)+len(except16)+len(except32))*2+
 			(len(range32))*4)
 
-	fmt.Printf("var isPrint16 = []uint16{\n")
+	fmt.Fprintf(&buf, "var isPrint16 = []uint16{\n")
 	for i := 0; i < len(range16); i += 2 {
-		fmt.Printf("\t%#04x, %#04x,\n", range16[i], range16[i+1])
+		fmt.Fprintf(&buf, "\t%#04x, %#04x,\n", range16[i], range16[i+1])
 	}
-	fmt.Printf("}\n\n")
+	fmt.Fprintf(&buf, "}\n\n")
 
-	fmt.Printf("var isNotPrint16 = []uint16{\n")
+	fmt.Fprintf(&buf, "var isNotPrint16 = []uint16{\n")
 	for _, r := range except16 {
-		fmt.Printf("\t%#04x,\n", r)
+		fmt.Fprintf(&buf, "\t%#04x,\n", r)
 	}
-	fmt.Printf("}\n\n")
+	fmt.Fprintf(&buf, "}\n\n")
 
-	fmt.Printf("var isPrint32 = []uint32{\n")
+	fmt.Fprintf(&buf, "var isPrint32 = []uint32{\n")
 	for i := 0; i < len(range32); i += 2 {
-		fmt.Printf("\t%#06x, %#06x,\n", range32[i], range32[i+1])
+		fmt.Fprintf(&buf, "\t%#06x, %#06x,\n", range32[i], range32[i+1])
 	}
-	fmt.Printf("}\n\n")
+	fmt.Fprintf(&buf, "}\n\n")
 
-	fmt.Printf("var isNotPrint32 = []uint16{ // add 0x10000 to each entry\n")
+	fmt.Fprintf(&buf, "var isNotPrint32 = []uint16{ // add 0x10000 to each entry\n")
 	for _, r := range except32 {
 		if r >= 0x20000 {
-			fmt.Fprintf(os.Stderr, "%U too big for isNotPrint32\n", r)
-			return
+			log.Fatalf("%U too big for isNotPrint32\n", r)
 		}
-		fmt.Printf("\t%#04x,\n", r-0x10000)
+		fmt.Fprintf(&buf, "\t%#04x,\n", r-0x10000)
+	}
+	fmt.Fprintf(&buf, "}\n")
+
+	data, err := format.Source(buf.Bytes())
+	if err != nil {
+		log.Fatal(err)
+	}
+	err = ioutil.WriteFile(*filename, data, 0644)
+	if err != nil {
+		log.Fatal(err)
 	}
-	fmt.Printf("}\n")
 }
diff --git a/libgo/go/strconv/quote.go b/libgo/go/strconv/quote.go
index aded7e5..53d51b5 100644
--- a/libgo/go/strconv/quote.go
+++ b/libgo/go/strconv/quote.go
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:generate go run makeisprint.go -output isprint.go
+
 package strconv
 
 import (
@@ -141,11 +143,21 @@ func AppendQuoteRuneToASCII(dst []byte, r rune) []byte {
 
 // CanBackquote reports whether the string s can be represented
 // unchanged as a single-line backquoted string without control
-// characters other than space and tab.
+// characters other than tab.
 func CanBackquote(s string) bool {
-	for i := 0; i < len(s); i++ {
-		c := s[i]
-		if (c < ' ' && c != '\t') || c == '`' || c == '\u007F' {
+	for len(s) > 0 {
+		r, wid := utf8.DecodeRuneInString(s)
+		s = s[wid:]
+		if wid > 1 {
+			if r == '\ufeff' {
+				return false // BOMs are invisible and should not be quoted.
+			}
+			continue // All other multibyte runes are correctly encoded and assumed printable.
+		}
+		if r == utf8.RuneError {
+			return false
+		}
+		if (r < ' ' && r != '\t') || r == '`' || r == '\u007F' {
 			return false
 		}
 	}
diff --git a/libgo/go/strconv/quote_test.go b/libgo/go/strconv/quote_test.go
index e4b5b6b..3bf162f 100644
--- a/libgo/go/strconv/quote_test.go
+++ b/libgo/go/strconv/quote_test.go
@@ -146,6 +146,10 @@ var canbackquotetests = []canBackquoteTest{
 	{`ABCDEFGHIJKLMNOPQRSTUVWXYZ`, true},
 	{`abcdefghijklmnopqrstuvwxyz`, true},
 	{`☺`, true},
+	{"\x80", false},
+	{"a\xe0\xa0z", false},
+	{"\ufeffabc", false},
+	{"a\ufeffz", false},
 }
 
 func TestCanBackquote(t *testing.T) {