In the future, how to keep runtime.KeepAlive from dead code elimination?

[Cholerae Hu]

Hi all,

I've read the source of package runtime, and found that runtime.KeepAlive is an empty function. If go compiler can do dead code elimination in the future, how to protect runtime.KeepAlive from being optimized?

[Ian Lance Taylor]

The KeepAlive function is marked with the magic go:noinline comment,
so it can't be inlined.

In any case it seems possible that the compiler will recognize the
function specially in the future, for greater efficiency.

Ian

[Cholerae Hu]

Does that mean that only inlined functions will be optimized and any functions not inlined will not be optimized ? 

在 2016年8月25日星期四 UTC+8上午11:55:12，Ian Lance Taylor写道：

[Dave Cheney]

Not really. Runtime.KeepAlive is special, it'll continue to be special in the future.

[Ian Lance Taylor]

On Thu, Aug 25, 2016 at 12:15 AM, Cholerae Hu <chole...@gmail.com> wrote:
> Does that mean that only inlined functions will be optimized and any
> functions not inlined will not be optimized ?

I'm not really sure what you are asking.

A function that is not inlined will not be inlined. That is
sufficient to ensure that runtime.KeepAlive works as intended.

A function that is not inlined, for whatever reason, will still be
optimized as usual.

Ian

> 在 2016年8月25日星期四 UTC+8上午11:55:12，Ian Lance Taylor写道：
>>
>> On Wed, Aug 24, 2016 at 7:06 PM, Cholerae Hu <chole...@gmail.com> wrote:
>> >
>> > I've read the source of package runtime, and found that
>> > runtime.KeepAlive is
>> > an empty function. If go compiler can do dead code elimination in the
>> > future, how to protect runtime.KeepAlive from being optimized?
>>
>> The KeepAlive function is marked with the magic go:noinline comment,
>> so it can't be inlined.
>>
>> In any case it seems possible that the compiler will recognize the
>> function specially in the future, for greater efficiency.
>>
>> Ian
>

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[Cholerae Hu]

I'm curious that how does compiler recognize runtime.KeepAlive specially?

在 2016年8月26日星期五 UTC+8上午12:04:57，Ian Lance Taylor写道：

[Dave Cheney]

runtime/mfinal.go:464

[Ian Lance Taylor]

On Fri, Aug 26, 2016 at 2:56 AM, Cholerae Hu <chole...@gmail.com> wrote:
> I'm curious that how does compiler recognize runtime.KeepAlive specially?

The compiler already recognizes some functions specially, most notably
math.Sqrt. Search for "Sqrt" in cmd/compile/internal/gc/walk.go.

Ian

[Cholerae Hu]

I see, thanks.

在 2016年8月25日星期四 UTC+8上午11:42:10，Cholerae Hu写道：