557404 - unatomize doubles

Status: RESOLVED DUPLICATE of bug 549143

(Core :: JavaScript Engine, defect)

Description

[Luke Wagner [:luke]]

Currently, literal double values are atomized.  This means a JSAtom* is either a (cast) JSString* or a double*.  It is questionable how much memory we are saving from atomizing doubles and it seems like we could make our code simpler and faster by dropping doubles and having a JSAtom* just be an opaque type signifying an atomized, untagged JSString*.

I'll take a crack at it.

Comment 1

[Luke Wagner [:luke]]

This is also good for the fat jsvals of bug 549143 and allows heap doubles to be totally wiped out, I think.

Comment 2

[Brendan Eich [:brendan]]

(In reply to comment #0)
> Currently, literal double values are atomized.  This means a JSAtom* is either
> a (cast) JSString* or a double*

... tagged as a jsval string or double (believe it!).

/be

Comment 3

[Luke Wagner [:luke]]

So, it seems that in the restricted domain of JSOP_LOOKUPSWITCH, atoms can be any non-primitive value.  However, only JSOP_LOOKUPSWITCH observes this, so perhaps we can change the way the immediate operands are encoded in the bytecode.

Comment 4

[Brendan Eich [:brendan]]

(In reply to comment #3)
> So, it seems that in the restricted domain of JSOP_LOOKUPSWITCH, atoms can be
> any non-primitive value.

s/non-//

/be

Comment 5

[Luke Wagner [:luke]]

Yes, thanks for both corrections.

So reading and thinking a bit more, it seems like bug 549143 can go ahead without removing heap doubles.  As long as they aren't being allocated in great quantity, the performance overhead will go away; the maintenance overhead can go away afterwards.

Comment 6

[Luke Wagner [:luke]]

fatvals ended up removing heap doubles altogether.