Add support for a ternary sub32 emitter for ARM64 and 32-bit ARM.

[Mark Lam]

We can use this to fix the FIXME in emitAllocateWithNonNullAllocator().

[Mark Lam]

Created attachment 288217 [details]
proposed patch.

[Mark Lam]

Looking into how to write a test for this now.

[Filip Pizlo]

Comment on attachment 288217 [details]
proposed patch.

View in context: https://bugs.webkit.org/attachment.cgi?id=288217&action=review

You ought to be able to write a test in testb3 that checks that we are now using the 3-operand sub.

> Source/JavaScriptCore/assembler/MacroAssemblerX86Common.h:568
> +    NO_RETURN_DUE_TO_CRASH void sub32(RegisterID, RegisterID, RegisterID)
> +    {
> +        RELEASE_ASSERT_NOT_REACHED();
> +    }
> +

Hmm.  I think we have an opportunity to make live a lot easier for ourselves if we implement this.  Here's a possible impl:

sub32(a, b, c)
{
    // Implement c = a - b
    if (c == b) {
        neg32(c);
        add32(a, c);
        return;
    }
    move(a, c);
    sub32(b, c);
}

[Mark Lam]

Created attachment 288310 [details]
proposed patch with test added and feedback applied.

[Mark Lam]

Thanks for the review.  Landed in r205656: <http://trac.webkit.org/r205656>.