刘桂祥,
Size and alignment guarantees
https://golang.org/ref/spec#Size_and_alignment_guarantees
A struct or array type has size zero if it contains no fields (or elements,
respectively) that have a size greater than zero. Two distinct zero-size
variables may have the same address in memory.
You have
type S struct{}
Why do you expect runtime.MemStats to show an allocation for zero bytes?
Peter
On Saturday, April 15, 2017 at 10:12:34 AM UTC-4, 刘桂祥 wrote:
>
>
> go build -gcflags '-N -l' example.go && ./example
> If I use this to compile example.go it shound disable function inline and
> the compile code should call ref() in example.go and will call mallocgc
> runtimestats.Mallocs can see it but it is not.
>
> 在 2017年4月14日星期五 UTC+8下午10:01:25，Ian Lance Taylor写道：
>>
>> On Thu, Apr 13, 2017 at 10:45 PM, 刘桂祥 <liuguix...@gmail.com> wrote:
>> > go1.7.1
>> >
>> > go run -gcflags '-N -l -m' example.go
>>
>> It is the -m flag that is generating the output you see.
>>
>> If there is some other bug, please let us know what it is.
>>
>> Ian
>>
>> > 在 2017年4月14日星期五 UTC+8下午1:18:26，Ian Lance Taylor写道：
>> >>
>> >> On Thu, Apr 13, 2017 at 8:33 PM, 刘桂祥 <liuguix...@gmail.com> wrote:
>> >> > // example.go
>> >> > package main
>> >> >
>> >> >
>> >> > import "runtime"
>> >> >
>> >> >
>> >> > type S struct{}
>> >> >
>> >> >
>> >> > func main() {
>> >> > var stats runtime.MemStats
>> >> >
>> >> >
>> >> > runtime.ReadMemStats(&stats)
>> >> > println(stats.Mallocs)
>> >> > var x S
>> >> > runtime.ReadMemStats(&stats)
>> >> > println(stats.Mallocs)
>> >> > _ = *ref(x)
>> >> > runtime.ReadMemStats(&stats)
>> >> > println(stats.Mallocs)
>> >> > }
>> >> >
>> >> >
>> >> > func ref(z S) *S {
>> >> > return &z
>> >> > }
>> >> >
>> >> > go build -gcflags '-N -l' example.go && ./example
>> >> > or
>> >> > go run -gcflags '-N -l' example.go
>> >> >
>> >> > results:
>> >> > ./example.go:21: &z escapes to heap
>> >> > ./example.go:20: moved to heap: z
>> >> > ./example.go:10: main &stats does not escape
>> >> > ./example.go:13: main &stats does not escape
>> >> > ./example.go:16: main &stats does not escape
>> >> > 61
>> >> > 61
>> >> > 61
>> >>
>> >> That looks like the output from -gcflags="-m -l". Are you really sure
>> >> you typed -N? What version of Go are you using?
>> >>
>> >> Ian
>> >
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