772255 - IonMonkey: LCreateThis should accept constant operands

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Sean Stangl [:sstangl]]

LCreateThis currently takes operands for the callee and the prototype. This causes generated code to assume the shape below, for repetitive invocations of LCreateThis on the same function:

> LPointer X
> LPointer Y
> LCreateThis (X, Y) -> Z
> LPointer X
> LPointer Y
> LCreateThis (X, Y) -> Z
> LPointer X
> LPointer Y
> LCreateThis (X, Y) -> Z

These pointers are only necessary for the slow callVM path, and they must be compile-time constants.

We could save on these loads by using local, manual register allocation and movePtr() in visitCreateThisVMCall() after the call to saveLive(). GC can be appeased via ImmGCPtr.

Comment 1

[Sean Stangl [:sstangl]]

Attachment: patch

Permits LCreateThis to bake in constants rather than depend on LPointer. Minor performance gain, probably mattering more in artificially tight loops involving allocation.

Comment 2

[David Anderson [:dvander] - inactive, e-mail if emergency]

Comment on attachment 640458 [details] [diff] [review]
patch

Review of attachment 640458 [details] [diff] [review]:
-----------------------------------------------------------------

::: js/src/ion/CodeGenerator.cpp
@@ +1441,5 @@
> +    GeneralRegisterSet regs = GeneralRegisterSet::All();
> +    if (proto->isRegister() && regs.has(ToRegister(proto)))
> +        regs.take(ToRegister(proto));
> +    if (callee->isRegister() && regs.has(ToRegister(callee)))
> +        regs.take(ToRegister(callee));

Why wouldn't it have the proto/callee regs? (you could takeUnchecked if proto might == callee but that sounds impossible)

@@ +1447,5 @@
> +
> +    // Push arguments.
> +    if (proto->isConstant()) {
> +        masm.movePtr(ImmGCPtr(&proto->toConstant()->toObject()), scratch);
> +        pushArg(scratch);

I don't think you need a scratch register, you can pushArg() an ImmGCPtr.

Comment 3

[Sean Stangl [:sstangl]]

http://hg.mozilla.org/projects/ionmonkey/rev/61bb4c14d50d