libgo: update to go1.9

    
    Reviewed-on: https://go-review.googlesource.com/63753

From-SVN: r252767

1 files changed, 88 insertions, 49 deletions

diff --git a/libgo/go/bytes/buffer.go b/libgo/go/bytes/buffer.go
index 196419d..20e42bb 100644
--- a/libgo/go/bytes/buffer.go
+++ b/libgo/go/bytes/buffer.go
@@ -15,10 +15,15 @@ import (
 // A Buffer is a variable-sized buffer of bytes with Read and Write methods.
 // The zero value for Buffer is an empty buffer ready to use.
 type Buffer struct {
-	buf       []byte   // contents are the bytes buf[off : len(buf)]
-	off       int      // read at &buf[off], write at &buf[len(buf)]
-	bootstrap [64]byte // memory to hold first slice; helps small buffers avoid allocation.
-	lastRead  readOp   // last read operation, so that Unread* can work correctly.
+	buf      []byte // contents are the bytes buf[off : len(buf)]
+	off      int    // read at &buf[off], write at &buf[len(buf)]
+	lastRead readOp // last read operation, so that Unread* can work correctly.
+	// FIXME: lastRead can fit in a single byte
+
+	// memory to hold first slice; helps small buffers avoid allocation.
+	// FIXME: it would be advisable to align Buffer to cachelines to avoid false
+	// sharing.
+	bootstrap [64]byte
 }
 
 // The readOp constants describe the last action performed on
@@ -68,13 +73,13 @@ func (b *Buffer) Cap() int { return cap(b.buf) }
 // but continues to use the same allocated storage.
 // It panics if n is negative or greater than the length of the buffer.
 func (b *Buffer) Truncate(n int) {
+	if n == 0 {
+		b.Reset()
+		return
+	}
 	b.lastRead = opInvalid
-	switch {
-	case n < 0 || n > b.Len():
+	if n < 0 || n > b.Len() {
 		panic("bytes.Buffer: truncation out of range")
-	case n == 0:
-		// Reuse buffer space.
-		b.off = 0
 	}
 	b.buf = b.buf[0 : b.off+n]
 }
@@ -82,7 +87,22 @@ func (b *Buffer) Truncate(n int) {
 // Reset resets the buffer to be empty,
 // but it retains the underlying storage for use by future writes.
 // Reset is the same as Truncate(0).
-func (b *Buffer) Reset() { b.Truncate(0) }
+func (b *Buffer) Reset() {
+	b.buf = b.buf[:0]
+	b.off = 0
+	b.lastRead = opInvalid
+}
+
+// tryGrowByReslice is a inlineable version of grow for the fast-case where the
+// internal buffer only needs to be resliced.
+// It returns the index where bytes should be written and whether it succeeded.
+func (b *Buffer) tryGrowByReslice(n int) (int, bool) {
+	if l := len(b.buf); l+n <= cap(b.buf) {
+		b.buf = b.buf[:l+n]
+		return l, true
+	}
+	return 0, false
+}
 
 // grow grows the buffer to guarantee space for n more bytes.
 // It returns the index where bytes should be written.
@@ -91,29 +111,33 @@ func (b *Buffer) grow(n int) int {
 	m := b.Len()
 	// If buffer is empty, reset to recover space.
 	if m == 0 && b.off != 0 {
-		b.Truncate(0)
+		b.Reset()
 	}
-	if len(b.buf)+n > cap(b.buf) {
-		var buf []byte
-		if b.buf == nil && n <= len(b.bootstrap) {
-			buf = b.bootstrap[0:]
-		} else if m+n <= cap(b.buf)/2 {
-			// We can slide things down instead of allocating a new
-			// slice. We only need m+n <= cap(b.buf) to slide, but
-			// we instead let capacity get twice as large so we
-			// don't spend all our time copying.
-			copy(b.buf[:], b.buf[b.off:])
-			buf = b.buf[:m]
-		} else {
-			// not enough space anywhere
-			buf = makeSlice(2*cap(b.buf) + n)
-			copy(buf, b.buf[b.off:])
-		}
+	// Try to grow by means of a reslice.
+	if i, ok := b.tryGrowByReslice(n); ok {
+		return i
+	}
+	// Check if we can make use of bootstrap array.
+	if b.buf == nil && n <= len(b.bootstrap) {
+		b.buf = b.bootstrap[:n]
+		return 0
+	}
+	if m+n <= cap(b.buf)/2 {
+		// We can slide things down instead of allocating a new
+		// slice. We only need m+n <= cap(b.buf) to slide, but
+		// we instead let capacity get twice as large so we
+		// don't spend all our time copying.
+		copy(b.buf[:], b.buf[b.off:])
+	} else {
+		// Not enough space anywhere, we need to allocate.
+		buf := makeSlice(2*cap(b.buf) + n)
+		copy(buf, b.buf[b.off:])
 		b.buf = buf
-		b.off = 0
 	}
-	b.buf = b.buf[0 : b.off+m+n]
-	return b.off + m
+	// Restore b.off and len(b.buf).
+	b.off = 0
+	b.buf = b.buf[:m+n]
+	return m
 }
 
 // Grow grows the buffer's capacity, if necessary, to guarantee space for
@@ -134,7 +158,10 @@ func (b *Buffer) Grow(n int) {
 // buffer becomes too large, Write will panic with ErrTooLarge.
 func (b *Buffer) Write(p []byte) (n int, err error) {
 	b.lastRead = opInvalid
-	m := b.grow(len(p))
+	m, ok := b.tryGrowByReslice(len(p))
+	if !ok {
+		m = b.grow(len(p))
+	}
 	return copy(b.buf[m:], p), nil
 }
 
@@ -143,7 +170,10 @@ func (b *Buffer) Write(p []byte) (n int, err error) {
 // buffer becomes too large, WriteString will panic with ErrTooLarge.
 func (b *Buffer) WriteString(s string) (n int, err error) {
 	b.lastRead = opInvalid
-	m := b.grow(len(s))
+	m, ok := b.tryGrowByReslice(len(s))
+	if !ok {
+		m = b.grow(len(s))
+	}
 	return copy(b.buf[m:], s), nil
 }
 
@@ -161,7 +191,7 @@ func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) {
 	b.lastRead = opInvalid
 	// If buffer is empty, reset to recover space.
 	if b.off >= len(b.buf) {
-		b.Truncate(0)
+		b.Reset()
 	}
 	for {
 		if free := cap(b.buf) - len(b.buf); free < MinRead {
@@ -225,7 +255,7 @@ func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) {
 		}
 	}
 	// Buffer is now empty; reset.
-	b.Truncate(0)
+	b.Reset()
 	return
 }
 
@@ -235,7 +265,10 @@ func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) {
 // ErrTooLarge.
 func (b *Buffer) WriteByte(c byte) error {
 	b.lastRead = opInvalid
-	m := b.grow(1)
+	m, ok := b.tryGrowByReslice(1)
+	if !ok {
+		m = b.grow(1)
+	}
 	b.buf[m] = c
 	return nil
 }
@@ -250,7 +283,10 @@ func (b *Buffer) WriteRune(r rune) (n int, err error) {
 		return 1, nil
 	}
 	b.lastRead = opInvalid
-	m := b.grow(utf8.UTFMax)
+	m, ok := b.tryGrowByReslice(utf8.UTFMax)
+	if !ok {
+		m = b.grow(utf8.UTFMax)
+	}
 	n = utf8.EncodeRune(b.buf[m:m+utf8.UTFMax], r)
 	b.buf = b.buf[:m+n]
 	return n, nil
@@ -264,7 +300,7 @@ func (b *Buffer) Read(p []byte) (n int, err error) {
 	b.lastRead = opInvalid
 	if b.off >= len(b.buf) {
 		// Buffer is empty, reset to recover space.
-		b.Truncate(0)
+		b.Reset()
 		if len(p) == 0 {
 			return
 		}
@@ -302,7 +338,7 @@ func (b *Buffer) ReadByte() (byte, error) {
 	b.lastRead = opInvalid
 	if b.off >= len(b.buf) {
 		// Buffer is empty, reset to recover space.
-		b.Truncate(0)
+		b.Reset()
 		return 0, io.EOF
 	}
 	c := b.buf[b.off]
@@ -320,7 +356,7 @@ func (b *Buffer) ReadRune() (r rune, size int, err error) {
 	b.lastRead = opInvalid
 	if b.off >= len(b.buf) {
 		// Buffer is empty, reset to recover space.
-		b.Truncate(0)
+		b.Reset()
 		return 0, 0, io.EOF
 	}
 	c := b.buf[b.off]
@@ -337,12 +373,12 @@ func (b *Buffer) ReadRune() (r rune, size int, err error) {
 
 // UnreadRune unreads the last rune returned by ReadRune.
 // If the most recent read or write operation on the buffer was
-// not a ReadRune, UnreadRune returns an error.  (In this regard
+// not a successful ReadRune, UnreadRune returns an error.  (In this regard
 // it is stricter than UnreadByte, which will unread the last byte
 // from any read operation.)
 func (b *Buffer) UnreadRune() error {
 	if b.lastRead <= opInvalid {
-		return errors.New("bytes.Buffer: UnreadRune: previous operation was not ReadRune")
+		return errors.New("bytes.Buffer: UnreadRune: previous operation was not a successful ReadRune")
 	}
 	if b.off >= int(b.lastRead) {
 		b.off -= int(b.lastRead)
@@ -351,12 +387,13 @@ func (b *Buffer) UnreadRune() error {
 	return nil
 }
 
-// UnreadByte unreads the last byte returned by the most recent
-// read operation. If write has happened since the last read, UnreadByte
-// returns an error.
+// UnreadByte unreads the last byte returned by the most recent successful
+// read operation that read at least one byte. If a write has happened since
+// the last read, if the last read returned an error, or if the read read zero
+// bytes, UnreadByte returns an error.
 func (b *Buffer) UnreadByte() error {
 	if b.lastRead == opInvalid {
-		return errors.New("bytes.Buffer: UnreadByte: previous operation was not a read")
+		return errors.New("bytes.Buffer: UnreadByte: previous operation was not a successful read")
 	}
 	b.lastRead = opInvalid
 	if b.off > 0 {
@@ -404,10 +441,12 @@ func (b *Buffer) ReadString(delim byte) (line string, err error) {
 	return string(slice), err
 }
 
-// NewBuffer creates and initializes a new Buffer using buf as its initial
-// contents. It is intended to prepare a Buffer to read existing data. It
-// can also be used to size the internal buffer for writing. To do that,
-// buf should have the desired capacity but a length of zero.
+// NewBuffer creates and initializes a new Buffer using buf as its
+// initial contents. The new Buffer takes ownership of buf, and the
+// caller should not use buf after this call. NewBuffer is intended to
+// prepare a Buffer to read existing data. It can also be used to size
+// the internal buffer for writing. To do that, buf should have the
+// desired capacity but a length of zero.
 //
 // In most cases, new(Buffer) (or just declaring a Buffer variable) is
 // sufficient to initialize a Buffer.