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reflect: fix _faststr optimization

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CL 345486 introduced an optimization to reflect's map accesses
which is not quite correct. We can't use the optimized code if the
value type is >128 bytes.

See cmd/compile/internal/walk/walk.go:mapfast

Fixes #48357

Change-Id: I8e3c7858693083dd4393a8de48ca5fa47bab66f2
Reviewed-on: https://go-review.googlesource.com/c/go/+/349593
Trust: Keith Randall <khr@golang.org>
Trust: Joe Tsai <joetsai@digital-static.net>
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Trust: Martin Möhrmann <martin@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
Run-TryBot: Joe Tsai <joetsai@digital-static.net>
Reviewed-by: Joe Tsai <joetsai@digital-static.net>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Martin Möhrmann <martin@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
This commit is contained in:
Keith Randall 2021-09-13 09:17:22 -07:00
parent c8a58f29dc
commit ac40c9872f
2 changed files with 22 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
src/reflect/value.go
View File

@ -1517,7 +1517,7 @@ func (v Value) MapIndex(key Value) Value {
// of unexported fields.
var e unsafe.Pointer
if key.kind() == String && tt.key.Kind() == String {
if key.kind() == String && tt.key.Kind() == String && tt.elem.size <= maxValSize {
k := *(*string)(key.ptr)
e = mapaccess_faststr(v.typ, v.pointer(), k)
} else {
@ -2128,7 +2128,7 @@ func (v Value) SetMapIndex(key, elem Value) {
key.mustBeExported()
tt := (*mapType)(unsafe.Pointer(v.typ))
if key.kind() == String && tt.key.Kind() == String {
if key.kind() == String && tt.key.Kind() == String && tt.elem.size <= maxValSize {
k := *(*string)(key.ptr)
if elem.typ == nil {
mapdelete_faststr(v.typ, v.pointer(), k)

20
test/fixedbugs/issue48357.go Normal file
View File

@ -0,0 +1,20 @@
// run
// Copyright 2021 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.
package main
import "reflect"
type T [129]byte
func main() {
m := map[string]T{}
v := reflect.ValueOf(m)
v.SetMapIndex(reflect.ValueOf("a"), reflect.ValueOf(T{}))
g = m["a"]
}
var g T