Gerriet, Take this with a huge grain of salt because I don’t know what’s
really going on here and whether the API will permit it, but the first
thing I would do is try to get the expensive operation outside any loop if
possible:
override function doSomething()
{
let ty = self.dynamicType
for index = 0 to hugeNumber step 3 // pseudo code
{
ty.setBitFieldAtIndex(index)
}
}
On Fri, Sep 9, 2016 at 2:54 AM, Gerriet M. Denkmann <gerr...@mdenkmann.de>
wrote:
> This code executes in a strange way: SubClass takes much longer than
> BaseClass.
>
> class BaseClass
> {
> let hugeNumber: Int
> var bitfield: UnsafeMutablePointer<UInt8>
>
> init()
> {
> hugeNumber = 1_000_000_000
> bitfield = calloc( hugeNumber, 1)
> }
>
> function doSomething()
> {
> for index = 0 to hugeNumber step 2 // pseudo code
> {
> self.dynamicType.setBitFieldAtIndex(index)
> }
> }
>
> class function setBitFieldAtIndex( index: Int )
> {
> bitfield[index] = 5
> }
> }
>
> final SubClass: BaseClass
> {
> override function doSomething()
> {
> for index = 0 to hugeNumber step 3 // pseudo code
> {
> self.dynamicType.setBitFieldAtIndex(index)
> }
> }
> }
>
> One assumes that SubClass is faster: it should take about 2/3 the time of
> BaseClass. But this is NOT the case.
>
> Instruments Time Profiler shows (total time, % of time, self time, name of
> function):
>
> BaseClass (does NOT override doSomething)
> 5743 ms 92.0% 644 doSomething
> Instruments shows only Assembly code
> 5099 ms 81.7% 4644 setBitFieldAtIndex
>
> SubClass (overrides doSomething)
> 8407 ms 92.6% 186 doSomething
> Instruments can show Swift code
> 2693 29.6% 2576
> setBitFieldAtIndex this about expected
> 2746 29.1% 2643 swift_retain
> (_swift::HeapObject) BAD
> 2643 29.1% 2643 swift_release
> (_swift::HeapObject) BAD
>
> I guess that in BaseClass doSomething gets inlined and the compiler knows
> that retain/release is not needed.
>
> So: How can I convince the compiler not to use retain/release in SubClass?
>
> Gerriet.
>
>
>
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--
Charles
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