Slightly more minimal, in my testing it seems that the call to 'nothing' is
not needed.
I do not quite know why, but these two lines seem to show how the compiler
is reasoning about this escape:
escape.go:4:11: flow: {heap} = x:
escape.go:4:11: from *y = x (assign) at escape.go:6:5
I do not know why it thinks assigning to '*y' is equivalent to assigning to
the heap; later it even mentions that `new([]byte) does not escape`, and
that is the definition of 'y'.
Sorry I'm not more helpful, I looked into this a bit more myself and also
came up without any good answers.
On Wednesday, March 4, 2020 at 2:58:37 PM UTC-7, burns...@gmail.com wrote:
>
> Hi All,
>
> I am trying to debug why a byte slice is escaping in my program. I have a
> small reproducible example here:
>
> % cat escape.go
> package main
>
> func main() {
> x := make([]byte, 5)
> y := new([]byte)
> *y = x
> nothing((*y)[3])
> }
>
> func nothing(b byte) {}
> % go tool compile -m -m -l escape.go
> escape.go:4:11: make([]byte, 5) escapes to heap:
> escape.go:4:11: flow: x = &{storage for make([]byte, 5)}:
> escape.go:4:11: from make([]byte, 5) (spill) at escape.go:4:11
> escape.go:4:11: from x := make([]byte, 5) (assign) at escape.go:4:4
> escape.go:4:11: flow: {heap} = x:
> escape.go:4:11: from *y = x (assign) at escape.go:6:5
> escape.go:4:11: make([]byte, 5) escapes to heap
> escape.go:5:10: new([]byte) does not escape
>
> It seems to me like neither x nor it's backing array should escape, but
> I'm having trouble figuring out why it's flagged as escaping from the debug
> output.
>
> % go version
> go version go1.14 darwin/amd64
>
>
> Any help would be appreciated.
>
> Ethan
>
>
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