CodeBlock::jettison() should be implicit
authorfpizlo@apple.com <fpizlo@apple.com@268f45cc-cd09-0410-ab3c-d52691b4dbfc>
Tue, 3 Sep 2013 16:39:29 +0000 (16:39 +0000)
committerfpizlo@apple.com <fpizlo@apple.com@268f45cc-cd09-0410-ab3c-d52691b4dbfc>
Tue, 3 Sep 2013 16:39:29 +0000 (16:39 +0000)
commit3db474cf662b64be1bea7cd0146689e27ebf1db8
treebbf5016ccc982b2133c824a26e2616b18e4084b1
parent2c0cda8db676f54e8c6cb1f5b252d7ad7eec48c6
CodeBlock::jettison() should be implicit
https://bugs.webkit.org/show_bug.cgi?id=120567

Reviewed by Oliver Hunt.

This is a risky change from a performance standpoint, but I believe it's
necessary. This makes all CodeBlocks get swept by GC. Nobody but the GC
can delete CodeBlocks because the GC always holds a reference to them.
Once a CodeBlock reaches just one reference (i.e. the one from the GC)
then the GC will free it only if it's not on the stack.

This allows me to get rid of the jettisoning logic. We need this for FTL
tier-up. Well; we don't need it, but it will help prevent a lot of bugs.
Previously, if you wanted to to replace one code block with another, you
had to remember to tell the GC that the previous code block is
"jettisoned". We would need to do this when tiering up from DFG to FTL
and when dealing with DFG-to-FTL OSR entry code blocks. There are a lot
of permutations here - tiering up to the FTL, OSR entering into the FTL,
deciding that an OSR entry code block is not relevant anymore - just to
name a few. In each of these cases we'd have to jettison the previous
code block. It smells like a huge source of future bugs.

So I made jettisoning implicit by making the GC always watch out for a
CodeBlock being owned solely by the GC.

This change is performance neutral.

* CMakeLists.txt:
* GNUmakefile.list.am:
* JavaScriptCore.vcxproj/JavaScriptCore.vcxproj:
* JavaScriptCore.xcodeproj/project.pbxproj:
* Target.pri:
* bytecode/CodeBlock.cpp:
(JSC::CodeBlock::CodeBlock):
(JSC::CodeBlock::~CodeBlock):
(JSC::CodeBlock::visitAggregate):
(JSC::CodeBlock::jettison):
* bytecode/CodeBlock.h:
(JSC::CodeBlock::setJITCode):
(JSC::CodeBlock::shouldImmediatelyAssumeLivenessDuringScan):
(JSC::CodeBlockSet::mark):
* dfg/DFGCommonData.h:
(JSC::DFG::CommonData::CommonData):
* heap/CodeBlockSet.cpp: Added.
(JSC::CodeBlockSet::CodeBlockSet):
(JSC::CodeBlockSet::~CodeBlockSet):
(JSC::CodeBlockSet::add):
(JSC::CodeBlockSet::clearMarks):
(JSC::CodeBlockSet::deleteUnmarkedAndUnreferenced):
(JSC::CodeBlockSet::traceMarked):
* heap/CodeBlockSet.h: Added.
* heap/ConservativeRoots.cpp:
(JSC::ConservativeRoots::add):
* heap/ConservativeRoots.h:
* heap/DFGCodeBlocks.cpp: Removed.
* heap/DFGCodeBlocks.h: Removed.
* heap/Heap.cpp:
(JSC::Heap::markRoots):
(JSC::Heap::deleteAllCompiledCode):
(JSC::Heap::deleteUnmarkedCompiledCode):
* heap/Heap.h:
* interpreter/JSStack.cpp:
(JSC::JSStack::gatherConservativeRoots):
* interpreter/JSStack.h:
* runtime/Executable.cpp:
(JSC::ScriptExecutable::installCode):
* runtime/Executable.h:
* runtime/VM.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@154986 268f45cc-cd09-0410-ab3c-d52691b4dbfc
22 files changed:
Source/JavaScriptCore/CMakeLists.txt
Source/JavaScriptCore/ChangeLog
Source/JavaScriptCore/GNUmakefile.list.am
Source/JavaScriptCore/JavaScriptCore.vcxproj/JavaScriptCore.vcxproj
Source/JavaScriptCore/JavaScriptCore.xcodeproj/project.pbxproj
Source/JavaScriptCore/Target.pri
Source/JavaScriptCore/bytecode/CodeBlock.cpp
Source/JavaScriptCore/bytecode/CodeBlock.h
Source/JavaScriptCore/dfg/DFGCommonData.h
Source/JavaScriptCore/heap/CodeBlockSet.cpp [new file with mode: 0644]
Source/JavaScriptCore/heap/CodeBlockSet.h [new file with mode: 0644]
Source/JavaScriptCore/heap/ConservativeRoots.cpp
Source/JavaScriptCore/heap/ConservativeRoots.h
Source/JavaScriptCore/heap/DFGCodeBlocks.cpp [deleted file]
Source/JavaScriptCore/heap/DFGCodeBlocks.h [deleted file]
Source/JavaScriptCore/heap/Heap.cpp
Source/JavaScriptCore/heap/Heap.h
Source/JavaScriptCore/interpreter/JSStack.cpp
Source/JavaScriptCore/interpreter/JSStack.h
Source/JavaScriptCore/runtime/Executable.cpp
Source/JavaScriptCore/runtime/Executable.h
Source/JavaScriptCore/runtime/VM.h