Then rewrite it this way
func SomeFunc() {
count:= 1
p := &count
total := 0
for i:=0;i<100000;i++ {
total = total + *p
someOtherFunc()
}
}
it should definitely be optimized away in this case.
> On Nov 30, 2018, at 12:09 PM, Jakob Borg <ja...@kastelo.net> wrote:
>
> This should only be valid for a loop that doesn’t include any function calls,
> or if the compiler can prove that said function calls don’t involve any
> synchronization primitives anywhere in the possible call stack.
>
> So maybe it’s optimized in
>
> for … {
> total += *p
> }
>
> but I wouldn’t bet on it in
>
> for … {
> total += *p
> foo()
> }
>
> //jb
>
>> On 30 Nov 2018, at 19:01, robert engels <reng...@ix.netcom.com
>> <mailto:reng...@ix.netcom.com>> wrote:
>>
>> I would think the compiler would be free to optimize this as a single load
>> outside the loop - as Go has no volatile declaration (to inform the compiler
>> that some other thread might of changed the value of *p)
>>
>>> On Nov 30, 2018, at 11:58 AM, robert engels <reng...@ix.netcom.com
>>> <mailto:reng...@ix.netcom.com>> wrote:
>>>
>>> It’s as simple as:
>>>
>>> var count = 1
>>> var p = &count
>>>
>>> func X() {
>>> total :=0
>>>
>>> for i:=0; i <1000000;i++ {
>>> total = total + *p
>>> }
>>> }
>>>
>>> no ?
>>>
>>>> On Nov 30, 2018, at 11:48 AM, Mark Volkmann <r.mark.volkm...@gmail.com
>>>> <mailto:r.mark.volkm...@gmail.com>> wrote:
>>>>
>>>> I think I failed to come up with a good code example. But suppose I need
>>>> to do something with a pointer inside a loop that really does require
>>>> dereferencing it and the pointer never changes inside the loop. In that
>>>> case will the Go compiler optimize that so the dereference doesn't happen
>>>> in each loop iteration?
>>>>
>>>> On Fri, Nov 30, 2018 at 11:36 AM Jan Mercl <0xj...@gmail.com
>>>> <mailto:0xj...@gmail.com>> wrote:
>>>>
>>>> On Fri, Nov 30, 2018 at 6:16 PM Mark Volkmann <r.mark.volkm...@gmail.com
>>>> <mailto:r.mark.volkm...@gmail.com>> wrote:
>>>>
>>>> > Will the Go compiler optimize the pointer dereference so it doesn't
>>>> > happen in every loop iteration? If not, is it common practice to do that
>>>> > outside the loop like this?
>>>> >
>>>> > myValue := *myPtr
>>>> > for _, v := range values {
>>>> > fmt.Printf("%v %v\n", myValue, v)
>>>> > }
>>>>
>>>> There's no pointer dereference inside the loop. But there's an allocation
>>>> inside the loop, on every iteration, that puts a pointer to a copy of
>>>> myValue into an interface{} that's passed to fmt.Printf. The allocation
>>>> can be probably avoided:
>>>>
>>>> myValue := interface{}(*myPtr)
>>>> for _, v := range values {
>>>> fmt.Printf("%v %v\n", myValue, v)
>>>> }
>>>>
>>>> But the %v verb handle pointers in many cases well. If that holds for the
>>>> type of *myPtr then simply:
>>>>
>>>> for _, v := range values {
>>>> fmt.Printf("%v %v\n", myPtr, v)
>>>> }
>>>>
>>>> is what could be good enough.
>>>>
>>>> --
>>>> -j
>>>>
>>>>
>>>>
>>>> --
>>>> R. Mark Volkmann
>>>> Object Computing, Inc.
>>>>
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