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cmd/cgo: don't emit C local if it is not used

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Fixes #76861

Change-Id: Icc8452e48ed736e8240f8afea18637c33b8e3ef8
Reviewed-on: https://go-review.googlesource.com/c/go/+/730600
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Joe Richey <joerichey@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Ian Lance Taylor 2025-12-16 16:00:36 -08:00 committed by Gopher Robot
parent 65b71c11d4
commit 8c28ab936a
3 changed files with 31 additions and 6 deletions
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12
src/cmd/cgo/internal/test/issue76861.go Normal file
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@ -0,0 +1,12 @@
// Copyright 2025 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.
//go:build cgo
package cgotest
// Issue 43639: No runtime test needed, make sure package
// cmd/cgo/internal/test/issue76861 compiles without error.
import _ "cmd/cgo/internal/test/issue76861"

13
src/cmd/cgo/internal/test/issue76861/a.go Normal file
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@ -0,0 +1,13 @@
// Copyright 2025 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 issue76861
// #cgo CFLAGS: -Wall -Werror
// void issue76861(void) {}
import "C"
func Issue76861() {
C.issue76861()
}

12
src/cmd/cgo/out.go
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@ -783,13 +783,13 @@ func (p *Package) writeOutputFunc(fgcc *os.File, n *Name) {
// We're trying to write a gcc struct that matches gc's layout.
// Use packed attribute to force no padding in this struct in case
// gcc has different packing requirements.
fmt.Fprintf(fgcc, "\t%s %v *_cgo_a = v;\n", ctype, p.packedAttribute())
if n.FuncType.Result != nil {
tr := n.FuncType.Result
if (n.Kind != "macro" && len(n.FuncType.Params) > 0) || tr != nil {
fmt.Fprintf(fgcc, "\t%s %v *_cgo_a = v;\n", ctype, p.packedAttribute())
}
if tr != nil {
// Save the stack top for use below.
fmt.Fprintf(fgcc, "\tchar *_cgo_stktop = _cgo_topofstack();\n")
}
tr := n.FuncType.Result
if tr != nil {
fmt.Fprintf(fgcc, "\t__typeof__(_cgo_a->r) _cgo_r;\n")
}
fmt.Fprintf(fgcc, "\t_cgo_tsan_acquire();\n")
@ -819,7 +819,7 @@ func (p *Package) writeOutputFunc(fgcc *os.File, n *Name) {
fmt.Fprintf(fgcc, "\t_cgo_errno = errno;\n")
}
fmt.Fprintf(fgcc, "\t_cgo_tsan_release();\n")
if n.FuncType.Result != nil {
if tr != nil {
// The cgo call may have caused a stack copy (via a callback).
// Adjust the return value pointer appropriately.
fmt.Fprintf(fgcc, "\t_cgo_a = (void*)((char*)_cgo_a + (_cgo_topofstack() - _cgo_stktop));\n")