1851226 - Optimize js_arena_malloc

Status: NEW

(Core :: Memory Allocator, enhancement)

Description

[Markus Stange [:mstange]]

Speedometer 3 spends 1.3% of the measured time in js_arena_malloc.

Profile: https://share.firefox.dev/3OT6ZcA

18% of it are in ArenaCollection::GetById, so if we can avoid the arena lookup, it should improve our sp3 score by 0.24%.
Improving overall sp3 by 0.24% is equivalent to improving a single subtest by 4.9%.

Here's a breakdown of the callers of js_arena_malloc: https://share.firefox.dev/3PmuIDo

• 22% are from js::NewStringCopyN during JSON.parse
• 13% ICStubSpace::alloc
• 7.5% JSRope::flatten
• Other