Bug 212765 – Add a Thread Specific Cache for LinkBuffer::CompactAndLinkCode()

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Michael Saboff]

Similar to https://bugs.webkit.org/show_bug.cgi?id=212562, we should add a Thread Local Buffer for LinkBuffer::copyCompactAndLinkCode().  When compacting JIT code, for most CPU types we need a second data buffer.  We should make this buffer a thread local just like we did for the AssemblerBuffer in 212562.

[Michael Saboff]

<rdar://problem/63986742>

[Michael Saboff]

Created attachment 401051 [details]
Patch

[Saam Barati]

Comment on attachment 401051 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=401051&action=review

r=me

> Source/JavaScriptCore/assembler/LinkBuffer.cpp:125
> +typedef ThreadSpecific<BranchCompactionLinkBuffer, WTF::CanBeGCThread::True> ThreadSpecificBranchCompactionLinkBuffer;

nit: "using" instead of "typedef"

> Source/JavaScriptCore/assembler/LinkBuffer.cpp:201
> +    uint8_t* m_data;
> +    size_t m_size;

nit: you can give these fields default values so you don't have to initialize them in 2 different ctors

> Source/JavaScriptCore/assembler/LinkBuffer.cpp:232
> +    BranchCompactionLinkBuffer outBuffer(m_size);

can we do the FAST_JIT_PERMISSIONS&&arm64e path above in a runtime supported way for other devices too? Seems purely better than this, since it doesn't require a side buffer.

There are a few arm64 devices that at runtime support APRR

Maybe as a follow-up in a separate patch

[Michael Saboff]

Created attachment 401067 [details]
Patch for landing

> > Source/JavaScriptCore/assembler/LinkBuffer.cpp:125
> > +typedef ThreadSpecific<BranchCompactionLinkBuffer, WTF::CanBeGCThread::True> ThreadSpecificBranchCompactionLinkBuffer;
> 
> nit: "using" instead of "typedef"

Done.

> > Source/JavaScriptCore/assembler/LinkBuffer.cpp:201
> > +    uint8_t* m_data;
> > +    size_t m_size;
> 
> nit: you can give these fields default values so you don't have to
> initialize them in 2 different ctors

Done.

[Michael Saboff]

Committed r262591: <https://trac.webkit.org/changeset/262591>