log/slog: use unsafe.StringData, SliceData

Use the new functions in 1.20 (unsafe.StringData, etc.) instead
of StringHeader and StructHeader from the reflect package.

Updates golang/go#56345.

Change-Id: I84d0db7b203aeffe45ce8b06beb7b4ee17e19949
Reviewed-on: https://go-review.googlesource.com/c/go/+/478055
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

diff --git a/src/log/slog/value_unsafe.go b/src/log/slog/value_unsafe.go
index 76266061f3a467e83748ee3c5f2d91819f80e3e3..4008ca51984a8788d067a49d868e8156390ad83a 100644 (file)
--- a/src/log/slog/value_unsafe.go
+++ b/src/log/slog/value_unsafe.go
@@ -5,7 +5,6 @@
 package slog
 
 import (
-       "reflect"
        "unsafe"
 )
 
@@ -29,8 +28,8 @@ type Value struct {
 }
 
 type (
-       stringptr unsafe.Pointer // used in Value.any when the Value is a string
-       groupptr  unsafe.Pointer // used in Value.any when the Value is a []Attr
+       stringptr *byte // used in Value.any when the Value is a string
+       groupptr  *Attr // used in Value.any when the Value is a []Attr
 )
 
 // Kind returns v's Kind.
@@ -55,16 +54,11 @@ func (v Value) Kind() Kind {
 
 // StringValue returns a new Value for a string.
 func StringValue(value string) Value {
-       hdr := (*reflect.StringHeader)(unsafe.Pointer(&value))
-       return Value{num: uint64(hdr.Len), any: stringptr(hdr.Data)}
+       return Value{num: uint64(len(value)), any: stringptr(unsafe.StringData(value))}
 }
 
 func (v Value) str() string {
-       var s string
-       hdr := (*reflect.StringHeader)(unsafe.Pointer(&s))
-       hdr.Data = uintptr(v.any.(stringptr))
-       hdr.Len = int(v.num)
-       return s
+       return unsafe.String(v.any.(stringptr), v.num)
 }
 
 // String returns Value's value as a string, formatted like fmt.Sprint. Unlike
@@ -72,20 +66,14 @@ func (v Value) str() string {
 // wrong kind, String never panics.
 func (v Value) String() string {
        if sp, ok := v.any.(stringptr); ok {
-               // Inlining this code makes a huge difference.
-               var s string
-               hdr := (*reflect.StringHeader)(unsafe.Pointer(&s))
-               hdr.Data = uintptr(sp)
-               hdr.Len = int(v.num)
-               return s
+               return unsafe.String(sp, v.num)
        }
        var buf []byte
        return string(v.append(buf))
 }
 
 func groupValue(as []Attr) Value {
-       hdr := (*reflect.SliceHeader)(unsafe.Pointer(&as))
-       return Value{num: uint64(hdr.Len), any: groupptr(hdr.Data)}
+       return Value{num: uint64(len(as)), any: groupptr(unsafe.SliceData(as))}
 }
 
 // group returns the Value's value as a []Attr.