On Thu, Apr 7, 2022 at 11:03 AM ワタナベハルキ <gt695348...@gmail.com> wrote:
>
> GOARCH="amd64"
> GOHOSTOS="linux"
> GOVERSION="go1.17.2"
>
> Here is my test code
>
> var sink *int
>
> func main(){
> escape()
> }
>
> // named return value r
> func escape() (r int) {
> defer func(){
> recover()
> }()
> sink = &r // escape r
> panic("qOeOp")
> return
> }
>
> jokoi@ubuntu:~/GoProJ/test$ go build -gcflags "-d defer" main.go
> ./main.go:11:2: stack-allocated defer
>
> and i find something comment may be useful in package
> cmd/compile/internel/ssagen
>
> if s.hasOpenDefers {
> ......
> // Similarly, skip if there are any heap-allocated result
> // parameters that need to be copied back to their stack
> slots.
> for _, f := range s.curfn.Type().Results().FieldSlice() {
> if !f.Nname.(*ir.Name).OnStack() {
> s.hasOpenDefers = false
> break
> }
> }
> }
> ......
> }
>
> but i cannot understand why ? As far as i know , coping heap-allocated result
> parameter back just need a small piece of code like mov rax [rax] at the exit
> point of one function , why compiler cannot generate it .
It was probably just never implemented. An escaping result parameter
is not a common case.
I expect the compiler developers would be happy to review a patch that
makes it work. See https://go.dev/doc/contribute.
Ian
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