1653027 - Strings to be atomized should be allocated as atoms, not copied

Status: NEW

(Core :: JavaScript: GC, enhancement, P3)

Description

[Steve Fink [:sfink] [:s:]]

When I added the heap argument to all the string allocation APIs, I also made a handful of places pass through TenuredHeap when they were allocating a string that was going to be atomized. My logic was that there's no point in nursery allocating a string only to copy its data over to a (tenured, by construction) atom.

Except that atomization always copies over the data, so the net effect of the above "optimization" is to produce a bunch of short-lived protostrings in the tenured heap. (js::Atomize unconditionally calls AtomizeAndCopyChars; it cannot morph a string in-place.)

We should have APIs that allow allocating atoms directly.