512686 - jit-compiled functions with optional args could have more entry points

Status: RESOLVED WONTFIX

(Tamarin Graveyard :: Baseline JIT (CodegenLIR), defect)

Description

[Edwin Smith]

In bug 512685, Lars notes:

   It would be a shame if otherwise early-bindable functions with
   optional args can't be handled like functions without optional
   args, ie, with the caller passing the required optional values
   and using a separate fast entry point.

Currently, such functions are jit-compiled with a single entry point that takes argc, then has branchy code in the prologue to initialize just the right number of arguments.

when a function is hot and being called from an early bound call-site, argc is constant at the call site.  we could instead generate N entry points, for each possible argc, and the call site can invoke the proper one, without passing in argc.

For late bound call sites, the dispatcher just has to invoke the right entry point once the target is known.

Another possible angle of attack is to generate the optional arguments at the call site, and make a call without passing argc and without initializing optional args in the callee.  this only works in AS3 if you cannot override a method and modify its optional arg values (need to double check).

Comment 1

[Steven Johnson]

(In reply to comment #0)
> this only works in AS3 if you cannot override a
> method and modify its optional arg values (need to double check).

Sadly, no:

	class A
	{
		function foo(a:int = 0) { return a; }
	}

	class B extends A
	{
		override function foo(a:int = 1) { return a; }
	}

	var a = new A;
	var b = new B;

	print(a.foo());
	print(b.foo());

compiles, runs, and yields

   0
   1

Comment 2

[Sylvestre Ledru [:Sylvestre]]

Tamarin is a dead project now. Mass WONTFIX.

Comment 3

[Sylvestre Ledru [:Sylvestre]]

Tamarin isn't maintained anymore. WONTFIX remaining bugs.