thanks a lot
在 2017年4月16日星期日 UTC+8上午12:22:13，peterGo写道：
>
>
> For this version of your program with
>
> type S struct{ B byte }
>
> There is an allocation,
>
> // example.go
> package main
>
> import (
> "runtime"
> "unsafe"
> )
>
> type S struct{ B byte }
>
> 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)
>
> println(unsafe.Sizeof(x))
> }
>
> func ref(z S) *S {
> return &z
> }
>
> Output:
>
> $ go version
> go version devel +bc29313 Fri Apr 14 16:47:25 2017 +0000 linux/amd64
> $ go run -gcflags '-N -l -m' example.go
> # command-line-arguments
> ./example.go:27:9: &z escapes to heap
> ./example.go:26:16: moved to heap: z
> ./example.go:14:23: main &stats does not escape
> ./example.go:17:23: main &stats does not escape
> ./example.go:20:23: main &stats does not escape
> 83
> 83
> 84
> 1
> $
>
> Peter
>
> On Saturday, April 15, 2017 at 12:14:48 PM UTC-4, peterGo wrote:
>>
>> 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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>>>> Groups
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>>>>
>>>
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