[webkit-reviews] review granted: [Bug 207616] [JSC] Compact StructureTransitionTable : [Attachment 390496] Patch

[bugzilla-daemon at webkit.org]

Mark Lam <mark.lam at apple.com> has granted Yusuke Suzuki <ysuzuki at apple.com>'s
request for review:
Bug 207616: [JSC] Compact StructureTransitionTable
https://bugs.webkit.org/show_bug.cgi?id=207616

Attachment 390496: Patch

https://bugs.webkit.org/attachment.cgi?id=390496&action=review




--- Comment #4 from Mark Lam <mark.lam at apple.com> ---
Comment on attachment 390496
  --> https://bugs.webkit.org/attachment.cgi?id=390496
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=390496&action=review

r=me

> Source/JavaScriptCore/ChangeLog:8
> +	   Some of StructureTransitionTable are shown as very large HashMap and
we can compact it by enconding key.

/enconding/encoding/

>> Source/JavaScriptCore/runtime/Structure.cpp:130
>> +   
map()->set(StructureTransitionTable::Hash::Key(structure->m_transitionPropertyN
ame.get(), +structure->transitionPropertyAttributes(),
!structure->isPropertyDeletionTransition()), structure);
> 
> is the + needed on +structure->transitionPropertyAttributes() and if it
isn't, should the comment above be removed? (I was able to build jsc with your
patch but with the + removed.)

I think this + is just accidental and can be removed.

> Source/JavaScriptCore/runtime/StructureTransitionTable.h:149
> +	   // using Key = std::tuple<UniquedStringImpl*, unsigned, bool>;

Can you make this std::tuple<UniquedStringImpl*, unsigned
transitionPropertyAttributes, bool isAddition> to better document the intended
purpose of those parameters?

> Source/JavaScriptCore/runtime/StructureTransitionTable.h:153
> +	       static constexpr uintptr_t stringMask = ((1ULL << 48) - 1) &
(~1ULL);
> +	       static constexpr uintptr_t isAdditionMask = 1ULL;

Let's swap these 2 and change stringMask to be:
    static constexpr uintptr_t stringMask = ((1ULL << 48) - 1) &
(~isAdditionMask);

This helps document that the lowest bit is where we store the isAddition flag.

> Source/JavaScriptCore/runtime/StructureTransitionTable.h:160
> +	       // Higher 16 bits for TransitionPropertyAttributes.
> +	       // Lower 1 bit for isAddition flag.

/Higher 16 bits for/Highest 16 bits are for/
/Lower 1 bit for/Lowest 1 bit is for/

> Source/JavaScriptCore/runtime/StructureTransitionTable.h:161
> +	       // Remaiing bits for UniquedStringImpl*.

/Remaiing bits for/Remaining bits are for/

> Source/JavaScriptCore/runtime/StructureTransitionTable.h:192
> +	       uintptr_t m_encodedData { 0 };

Let's make this private.  If needed, make struct Hash a friend.