fmt.Println cause memory escape

[qdongxu]

What version of Go are you using (go version)?

$ go version
go version go1.11.4 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GOARCH="amd64"
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/hg/4yk5n5f551z8v950nxkq9bf80000gn/T/go-build076297954=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

package main

import (
	"fmt"
	"time"
)

func main() {
	for i := 0; i < 5; i++ {
        m := i
        fmt.Println("outer: ", m)
        go func(j int) {
            k := j
            fmt.Println("innter", k)
        }(i)
	}

	time.Sleep(1 * time.Second)
    s := "Done"
	fmt.Println(s)
}

% go build --gcflags '-m -l'  x.go
# command-line-arguments
./x.go:11:21: "outer: " escapes to heap
./x.go:11:21: m escapes to heap
./x.go:12:12: func literal escapes to heap
./x.go:12:12: func literal escapes to heap
./x.go:20:13: s escapes to heap
./x.go:14:25: "innter" escapes to heap
./x.go:14:25: k escapes to heap
./x.go:11:20: main ... argument does not escape
./x.go:20:13: main ... argument does not escape
./x.go:14:24: main.func1 ... argument does not escape

As we can see, the const strings, the variable j are allocated on heap, but they can be alloced on stack, by a easy manually check.

What did you expect to see?

the golang library funciton fmt.Println should not cause memory escape.

What did you see instead?

parameters passed into fmt.Println escaped to heap.

[qdongxu]

Looks there's already reported by #7710

[randall77]

I think the right dup is #19720

TL;DR It would be nice to fix, but this is hard. It requires type-dependent escape analysis.

[zigo101]

The still opening one #8618

[bcmills]

Duplicate of #8618