CodeBlock should have a more explicit "strongly referenced" state
https://bugs.webkit.org/show_bug.cgi?id=148714
Reviewed by Filip Pizlo.
Previously, CodeBlock had a "may be executing" bit, which was used by
both the stack visitor and the compiler to indicate "this CodeBlock must
not jettison itself".
Now, CodeBlock has an explicit "is strongly referenced" bit to do the
same.
For now, there is no behavior change. In future, I will use the "is
strongly referenced" bit to indicate the set of all references that
cause a CodeBlock not to jettison itself. Strong references and stack
references will be different because:
(1) A stack reference requires a write barrier at the end of GC
(since CodeBlocks only barrier themselves on function entry,
and GC will clear that barrier); but a strong reference does not
need or want a write barrier at the end of GC.
(2) Visiting more heap objects might reveal more strong references
but, by definition, it cannot reveal more stack references.
Also, this patch adds an explicit mark clearing phase for compiler
CodeBlocks, which does the work that would normally be done by a write
barrier. A compiler CodeBlock can't rely on a normal write barrier
because the compiler writes to CodeBlocks without invoking a write
barrier, and because the CodeBlock write barrier operates on an
executable, but an in-flight compilation is not pointed to by any
executable. This bug does not appear to be noticeable in the current
system, but I will probably make it noticeable.
* bytecode/CodeBlock.cpp:
(JSC::CodeBlock::CodeBlock):
(JSC::CodeBlock::shouldImmediatelyAssumeLivenessDuringScan):
(JSC::CodeBlock::isKnownToBeLiveDuringGC):
* bytecode/CodeBlock.h:
(JSC::ExecState::uncheckedR):
(JSC::CodeBlockSet::clearMarks):
(JSC::CodeBlockSet::mark):
* dfg/DFGPlan.cpp:
(JSC::DFG::Plan::key):
(JSC::DFG::Plan::clearCodeBlockMarks):
(JSC::DFG::Plan::checkLivenessAndVisitChildren):
* dfg/DFGPlan.h:
* dfg/DFGWorklist.cpp:
(JSC::DFG::Worklist::completeAllPlansForVM):
(JSC::DFG::Worklist::clearCodeBlockMarks):
(JSC::DFG::Worklist::suspendAllThreads):
(JSC::DFG::Worklist::visitWeakReferences):
(JSC::DFG::completeAllPlansForVM):
(JSC::DFG::clearCodeBlockMarks):
* dfg/DFGWorklist.h:
(JSC::DFG::worklistForIndexOrNull):
* heap/CodeBlockSet.cpp:
(JSC::CodeBlockSet::clearMarksForFullCollection):
(JSC::CodeBlockSet::clearMarksForEdenCollection):
(JSC::CodeBlockSet::deleteUnmarkedAndUnreferenced):
(JSC::CodeBlockSet::traceMarked):
(JSC::CodeBlockSet::rememberCurrentlyExecutingCodeBlocks):
* heap/CodeBlockSet.h:
* heap/Heap.cpp:
(JSC::Heap::markRoots):
git-svn-id: http://svn.webkit.org/repository/webkit/trunk@189257 268f45cc-cd09-0410-ab3c-d52691b4dbfc
10 files changed
