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cmd/compile: correct alignment of atomic.Int64

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Same as CL 417555, but for cmd/compile.

Fixes #54220

Change-Id: I4cc6deaf0a87c952f636888b4ab73f81a44bfebd
Reviewed-on: https://go-review.googlesource.com/c/go/+/420975
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Keith Randall <khr@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
This commit is contained in:
Cuong Manh Le 2022-08-03 15:14:25 +07:00
parent 9463638ca8
commit 3ea3d0e8a7
3 changed files with 39 additions and 2 deletions
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11
src/cmd/compile/internal/noder/sizes.go
View File

@ -25,6 +25,17 @@ func (s *gcSizes) Alignof(T types2.Type) int64 {
// is the same as unsafe.Alignof(x[0]), but at least 1."
return s.Alignof(t.Elem())
case *types2.Struct:
if t.NumFields() == 0 && types2.IsSyncAtomicAlign64(T) {
// Special case: sync/atomic.align64 is an
// empty struct we recognize as a signal that
// the struct it contains must be
// 64-bit-aligned.
//
// This logic is equivalent to the logic in
// cmd/compile/internal/types/size.go:calcStructOffset
return 8
}
// spec: "For a variable x of struct type: unsafe.Alignof(x)
// is the largest of the values unsafe.Alignof(x.f) for each
// field f of x, but at least 1."

4
src/cmd/compile/internal/types2/sizes.go
View File

@ -53,7 +53,7 @@ func (s *StdSizes) Alignof(T Type) int64 {
// is the same as unsafe.Alignof(x[0]), but at least 1."
return s.Alignof(t.elem)
case *Struct:
if len(t.fields) == 0 && isSyncAtomicAlign64(T) {
if len(t.fields) == 0 && IsSyncAtomicAlign64(T) {
// Special case: sync/atomic.align64 is an
// empty struct we recognize as a signal that
// the struct it contains must be
@ -104,7 +104,7 @@ func (s *StdSizes) Alignof(T Type) int64 {
return a
}
func isSyncAtomicAlign64(T Type) bool {
func IsSyncAtomicAlign64(T Type) bool {
named, ok := T.(*Named)
if !ok {
return false

26
test/fixedbugs/issue54220.go Normal file
View File

@ -0,0 +1,26 @@
// run
// Copyright 2022 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 (
"strconv"
"sync/atomic"
"unsafe"
)
type t struct {
i1 atomic.Int32
i2 atomic.Int64
}
var v t
func main() {
if o := unsafe.Offsetof(v.i2); o != 8 {
panic("unexpected offset, want: 8, got: " + strconv.Itoa(int(o)))
}
}