1810160 - De-duplicate bytecode within single compilation

Status: ASSIGNED

(Core :: JavaScript Engine, task, P3)

Description

[Tooru Fujisawa [:arai]]

Single compilation unit can contain multiple duplicated bytecode especially for small function (e.g. ~3000 duplicated entries within 12000 entries in gmail JS file), and performing all de-duplication on instantiation on main thread is not optimal.

Performing compilation-local deduplication off-main-thread will:

• reduce the task requred on main thread instantiation
• reduce the XDR bytecode size

Comment 1

[Tooru Fujisawa [:arai]]

Attachment: Bug 1810160 - Part 1: Perform SharedImmutableScriptData::shareScriptData during instantiation. r?tcampbell!

Re-landing of bug 1805149 patches Part 1 and 2.

Comment 2

[Tooru Fujisawa [:arai]]

Attachment: Bug 1810160 - Part 2: Perform local bytecode de-duplication during compilation. r?tcampbell!

Now ScriptStencil to SharedImmutableScriptData is not 1:1, and ScriptStencil
holds SharedImmutableScriptDataIndex to point the SharedImmutableScriptData
inside SharedDataContainer.

SharedDataContainer is simplified to use either a single pointer or a vector.

Comment 3

[Tooru Fujisawa [:arai]]

Attachment: Bug 1810160 - Part 3: Perform global bytecode de-duplication at once. r?tcampbell!

Comment 4

[Tooru Fujisawa [:arai]]

Attachment: Bug 1810160 - Part 4: Remove AutoLockScriptData. r?tcampbell!

Comment 5

[Tooru Fujisawa [:arai]]

bug 1814550 unblocks the JSContext removal

Comment 6

[Tooru Fujisawa [:arai]]

local bytecode de-duplication can still be valuable for reducing memory consumption and also reducing XDR data size.
we can revisit this later, maybe by conditionally applying the local de-duplication only for large file, or only to files that will be XDR encoded.
also possibly with special casing small/empty functions to represent them with static data.