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digitalmars.D.learn - delegates & GC allocations

reply Etienne <etcimon gmail.com> writes:
I've been hearing that delegates get a context pointer which will be 
allocated on the GC. Is this also true for delegates which stay in scope?

e.g.

void addThree() {
	int val;
	void addOne() {
		val++;
	}
	
	addOne();
	addOne();
	addOne();

	return val;
}

Will the above function allocate on the GC?
Aug 20 2014
next sibling parent ketmar via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
On Wed, 20 Aug 2014 10:44:38 -0400
Etienne via Digitalmars-d-learn <digitalmars-d-learn puremagic.com>
wrote:


 Will the above function allocate on the GC?


no.
Aug 20 2014
prev sibling next sibling parent reply ketmar via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
On Wed, 20 Aug 2014 10:44:38 -0400
Etienne via Digitalmars-d-learn <digitalmars-d-learn puremagic.com>
wrote:

and this is not delegate, this is just nested function.
Aug 20 2014
parent reply "Dicebot" <public dicebot.lv> writes:
On Wednesday, 20 August 2014 at 14:54:31 UTC, ketmar via 
Digitalmars-d-learn wrote:

 On Wed, 20 Aug 2014 10:44:38 -0400
 Etienne via Digitalmars-d-learn 
 <digitalmars-d-learn puremagic.com>
 wrote:

 and this is not delegate, this is just nested function.


non-static nested functions are effectively delegates as it needs 
a context pointer to parent stack frame. However, not every 
delegate is a closure - heap allocation of the context happens 
only if delegate leaves the scope it refers to (via return value 
or by being passed as an argument to external function)
Aug 20 2014
parent reply "Ola Fosheim Gr" <ola.fosheim.grostad+dlang gmail.com> writes:
 non-static nested functions are effectively delegates as it 
 needs a context pointer to parent stack frame.


Only if it is recursive.
Aug 20 2014
parent reply "Chris Nicholson-Sauls" <ibisbasenji gmail.com> writes:
On Wednesday, 20 August 2014 at 15:17:52 UTC, Ola Fosheim Gr 
wrote:

 non-static nested functions are effectively delegates as it 
 needs a context pointer to parent stack frame.


 Only if it is recursive.


Or if it refers to any state of the parent function.
Aug 20 2014
parent reply "Ola Fosheim Gr" <ola.fosheim.grostad+dlang gmail.com> writes:
On Wednesday, 20 August 2014 at 20:48:38 UTC, Chris 
Nicholson-Sauls wrote:

 On Wednesday, 20 August 2014 at 15:17:52 UTC, Ola Fosheim Gr 
 wrote:

 non-static nested functions are effectively delegates as it 
 needs a context pointer to parent stack frame.


 Only if it is recursive.


 Or if it refers to any state of the parent function.


As long as the compiler knows where it will be called from it 
should be able use a stack pointer offset (unless alloca gets in 
the way) without the frame pointer of the parent.
Aug 20 2014
parent reply "Ola Fosheim Gr" <ola.fosheim.grostad+dlang gmail.com> writes:
On Wednesday, 20 August 2014 at 21:19:18 UTC, Ola Fosheim Gr 
wrote:

 On Wednesday, 20 August 2014 at 20:48:38 UTC, Chris 
 Nicholson-Sauls wrote:

 On Wednesday, 20 August 2014 at 15:17:52 UTC, Ola Fosheim Gr 
 wrote:

 Only if it is recursive.


 Or if it refers to any state of the parent function.


 As long as the compiler knows where it will be called from it 
 should be able use a stack pointer offset (unless alloca gets 
 in the way) without the frame pointer of the parent.


Well, I guess simple recursion could be solved easily too by 
having a wrapper function that puts the frame pointer in a free 
callee save register...
Aug 20 2014
parent reply Etienne <etcimon gmail.com> writes:
On 2014-08-20 5:25 PM, Ola Fosheim Gr wrote:

 Well, I guess simple recursion could be solved easily too by having a
 wrapper function that puts the frame pointer in a free callee save
 register...


So, my question inspired a new optimization? :-p
Aug 20 2014
parent "Ola Fosheim Gr" <ola.fosheim.grostad+dlang gmail.com> writes:
On Wednesday, 20 August 2014 at 21:30:41 UTC, Etienne wrote:

 So, my question inspired a new optimization? :-p


A decent optimizing compiler would detect that the function is 
calling itself and save stack space by using register where 
possible...
Aug 20 2014
prev sibling parent "hane" <han.ehit.suzi.0 gmail.com> writes:
On Wednesday, 20 August 2014 at 14:44:39 UTC, Etienne wrote:

 I've been hearing that delegates get a context pointer which 
 will be allocated on the GC. Is this also true for delegates 
 which stay in scope?

 e.g.

 void addThree() {
 	int val;
 	void addOne() {
 		val++;
 	}
 	
 	addOne();
 	addOne();
 	addOne();

 	return val;
 }

 Will the above function allocate on the GC?


int getInt1()  nogc
{
	int val;
	int func()  nogc { return val; }
	return func();
}

int delegate() getInt2() // nogc - thie one allocates!
{
	int val;
	int func()  nogc { return val; }
	return &func;
}

int delegate() getInt3()  nogc
{
	int val;
	int func()  nogc { return 0; }
	return &func;
}
Aug 20 2014