debug/dwarf: optimize buf.string

(*buf).string previously manually searched
through its underlying byte slice until we
encountered a '0'. This change instead uses
bytes.IndexByte that results in a speed up:

$ benchstat before.txt after.txt

name         old time/op    new time/op    delta
BufString-8     257ns ± 1%     174ns ± 1%  -32.37%  (p=0.000 n=9+8)

name         old speed      new speed      delta
BufString-8   495MB/s ± 1%   732MB/s ± 1%  +47.76%  (p=0.000 n=10+8)

name         old alloc/op   new alloc/op   delta
BufString-8      162B ± 0%      162B ± 0%     ~     (all equal)

name         old allocs/op  new allocs/op  delta
BufString-8      3.00 ± 0%      3.00 ± 0%     ~     (all equal)

Change-Id: I7cf241742cc091d5d30d987a168b02d83955b1cf
Reviewed-on: https://go-review.googlesource.com/c/go/+/196657
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

diff --git a/src/debug/dwarf/buf.go b/src/debug/dwarf/buf.go
index 3e6ce293fd35d4e4622e9ec3856860e9d1b393fc..c3822a0dac713940832522945244bb1d523bbda5 100644 (file)
--- a/src/debug/dwarf/buf.go
+++ b/src/debug/dwarf/buf.go
@@ -7,6 +7,7 @@
 package dwarf
 
 import (
+       "bytes"
        "encoding/binary"
        "strconv"
 )
@@ -79,16 +80,16 @@ func (b *buf) bytes(n int) []byte {
 func (b *buf) skip(n int) { b.bytes(n) }
 
 func (b *buf) string() string {
-       for i := 0; i < len(b.data); i++ {
-               if b.data[i] == 0 {
-                       s := string(b.data[0:i])
-                       b.data = b.data[i+1:]
-                       b.off += Offset(i + 1)
-                       return s
-               }
+       i := bytes.IndexByte(b.data, 0)
+       if i < 0 {
+               b.error("underflow")
+               return ""
        }
-       b.error("underflow")
-       return ""
+
+       s := string(b.data[0:i])
+       b.data = b.data[i+1:]
+       b.off += Offset(i + 1)
+       return s
 }
 
 func (b *buf) uint16() uint16 {