Bug 228053 – DFGByteCodeParser.cpp should avoid resizing the Operands<> of every BasicBlock on every inlining

• Status: REOPENED
• Component: JavaScriptCore

[Robin Morisset]

The dfg bytecode parser only makes use of block->variablesAtTail. But currently it updates the size of variablesAtHead, valuesAtHead, valuesAtTail and intersectionOfPastValuesAtHead every single time it changes the number of Tmps and/or Locals. This happens notably whenever it inlines a function.
It is not nearly as cheap as it looks, as each resizing may reallocate a Vector, requires filling the new slots with zeros, and requires moving the existing values (which are all 0) to the new Vector. This was obvious when looking at profiling of JS2: bzero + memmove are the two hottest C++ functions, and the manipulation of Operands is partly responsible.
It can be easily improved: only resize block->variablesAtTail on inlining, and initialize all of the other operands at the very end of the DFGByteCodeParser.

[Robin Morisset]

Created attachment 433740 [details]
Patch

[Robin Morisset]

Created attachment 433742 [details]
Patch

updated Changelog with perf numbers.

[Robin Morisset]

Created attachment 433743 [details]
Patch

Fix style nitpick.

[Radar WebKit Bug Importer]

<rdar://problem/81064797>

[Saam Barati]

Comment on attachment 433743 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=433743&action=review

r=me

> Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp:8971
> +        block->variablesAtHead = Operands<Node*>(m_numArguments, m_numLocals, m_numTmps);
> +        block->valuesAtHead = Operands<AbstractValue>(m_numArguments, m_numLocals, m_numTmps);
> +        block->valuesAtTail = Operands<AbstractValue>(m_numArguments, m_numLocals, m_numTmps);
> +        block->intersectionOfPastValuesAtHead = Operands<AbstractValue>(m_numArguments, m_numLocals, m_numTmps);

nit: Use the OperandsLike constructor so these lines of code don't have to change in the future if we change the Operands constructor you're invoking?

[Robin Morisset]

Created attachment 444624 [details]
Patch

Applied Saam's suggestion and rebased

[EWS]

Committed r286030 (244418@main): <https://commits.webkit.org/244418@main>

All reviewed patches have been landed. Closing bug and clearing flags on attachment 444624 [details].

[WebKit Commit Bot]

Re-opened since this is blocked by bug 233387