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/*
* Copyright (C) 2018-2021 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "ExecutableToCodeBlockEdge.h"
#include "CodeBlock.h"
#include "IsoCellSetInlines.h"
#include "JSObjectInlines.h"
#include "StructureInlines.h"
namespace JSC {
const ClassInfo ExecutableToCodeBlockEdge::s_info = { "ExecutableToCodeBlockEdge", nullptr, nullptr, nullptr, CREATE_METHOD_TABLE(ExecutableToCodeBlockEdge) };
Structure* ExecutableToCodeBlockEdge::createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype)
{
return Structure::create(vm, globalObject, prototype, TypeInfo(CellType, StructureFlags), info());
}
ExecutableToCodeBlockEdge* ExecutableToCodeBlockEdge::create(VM& vm, CodeBlock* codeBlock)
{
ExecutableToCodeBlockEdge* result = new (NotNull, allocateCell<ExecutableToCodeBlockEdge>(vm.heap)) ExecutableToCodeBlockEdge(vm, codeBlock);
result->finishCreation(vm);
return result;
}
void ExecutableToCodeBlockEdge::finishCreation(VM& vm)
{
Base::finishCreation(vm);
ASSERT(!isActive());
}
template<typename Visitor>
void ExecutableToCodeBlockEdge::visitChildrenImpl(JSCell* cell, Visitor& visitor)
{
VM& vm = visitor.vm();
ExecutableToCodeBlockEdge* edge = jsCast<ExecutableToCodeBlockEdge*>(cell);
ASSERT_GC_OBJECT_INHERITS(cell, info());
Base::visitChildren(cell, visitor);
CodeBlock* codeBlock = edge->m_codeBlock.get();
// It's possible for someone to hold a pointer to the edge after the edge has cleared its weak
// reference to the codeBlock. In a conservative GC like ours, that could happen at random for
// no good reason and it's Totally OK (TM). See finalizeUnconditionally() for where we clear
// m_codeBlock.
if (!codeBlock)
return;
if (!edge->isActive()) {
visitor.appendUnbarriered(codeBlock);
return;
}
ConcurrentJSLocker locker(codeBlock->m_lock);
if (codeBlock->shouldVisitStrongly(locker, visitor))
visitor.appendUnbarriered(codeBlock);
if (!visitor.isMarked(codeBlock))
vm.executableToCodeBlockEdgesWithFinalizers.add(edge);
if (JITCode::isOptimizingJIT(codeBlock->jitType())) {
// If we jettison ourselves we'll install our alternative, so make sure that it
// survives GC even if we don't.
visitor.append(codeBlock->m_alternative);
}
// NOTE: There are two sides to this constraint, with different requirements for correctness.
// Because everything is ultimately protected with weak references and jettisoning, it's
// always "OK" to claim that something is dead prematurely and it's "OK" to keep things alive.
// But both choices could lead to bad perf - either recomp cycles or leaks.
//
// Determining CodeBlock liveness: This part is the most consequential. We want to keep the
// output constraint active so long as we think that we may yet prove that the CodeBlock is
// live but we haven't done it yet.
//
// Marking Structures if profitable: It's important that we do a pass of this. Logically, this
// seems like it is a constraint of CodeBlock. But we have always first run this as a result
// of the edge being marked even before we determine the liveness of the CodeBlock. This
// allows a CodeBlock to mark itself by first proving that all of the Structures it weakly
// depends on could be strongly marked. (This part is also called propagateTransitions.)
//
// As a weird caveat, we only fixpoint the constraints so long as the CodeBlock is not live.
// This means that we may overlook structure marking opportunities created by other marking
// that happens after the CodeBlock is marked. This was an accidental policy decision from a
// long time ago, but it is probably OK, since it's only worthwhile to keep fixpointing the
// structure marking if we still have unmarked structures after the first round. We almost
// never will because we will mark-if-profitable based on the owning global object being
// already marked. We mark it just in case that hadn't happened yet. And if the CodeBlock is
// not yet marked because it weakly depends on a structure that we did not yet mark, then we
// will keep fixpointing until the end.
visitor.appendUnbarriered(codeBlock->globalObject());
vm.executableToCodeBlockEdgesWithConstraints.add(edge);
edge->runConstraint(locker, vm, visitor);
}
DEFINE_VISIT_CHILDREN(ExecutableToCodeBlockEdge);
template<typename Visitor>
void ExecutableToCodeBlockEdge::visitOutputConstraintsImpl(JSCell* cell, Visitor& visitor)
{
VM& vm = visitor.vm();
ExecutableToCodeBlockEdge* edge = jsCast<ExecutableToCodeBlockEdge*>(cell);
edge->runConstraint(NoLockingNecessary, vm, visitor);
}
DEFINE_VISIT_OUTPUT_CONSTRAINTS(ExecutableToCodeBlockEdge);
void ExecutableToCodeBlockEdge::finalizeUnconditionally(VM& vm)
{
CodeBlock* codeBlock = m_codeBlock.get();
if (!vm.heap.isMarked(codeBlock)) {
if (codeBlock->shouldJettisonDueToWeakReference(vm))
codeBlock->jettison(Profiler::JettisonDueToWeakReference);
else
codeBlock->jettison(Profiler::JettisonDueToOldAge);
m_codeBlock.clear();
}
vm.executableToCodeBlockEdgesWithFinalizers.remove(this);
vm.executableToCodeBlockEdgesWithConstraints.remove(this);
}
inline void ExecutableToCodeBlockEdge::activate()
{
setPerCellBit(true);
}
inline void ExecutableToCodeBlockEdge::deactivate()
{
setPerCellBit(false);
}
inline bool ExecutableToCodeBlockEdge::isActive() const
{
return perCellBit();
}
CodeBlock* ExecutableToCodeBlockEdge::deactivateAndUnwrap(ExecutableToCodeBlockEdge* edge)
{
if (!edge)
return nullptr;
edge->deactivate();
return edge->codeBlock();
}
ExecutableToCodeBlockEdge* ExecutableToCodeBlockEdge::wrap(CodeBlock* codeBlock)
{
if (!codeBlock)
return nullptr;
return codeBlock->ownerEdge();
}
ExecutableToCodeBlockEdge* ExecutableToCodeBlockEdge::wrapAndActivate(CodeBlock* codeBlock)
{
if (!codeBlock)
return nullptr;
ExecutableToCodeBlockEdge* result = codeBlock->ownerEdge();
result->activate();
return result;
}
ExecutableToCodeBlockEdge::ExecutableToCodeBlockEdge(VM& vm, CodeBlock* codeBlock)
: Base(vm, vm.executableToCodeBlockEdgeStructure.get())
, m_codeBlock(vm, this, codeBlock)
{
}
template<typename Visitor>
void ExecutableToCodeBlockEdge::runConstraint(const ConcurrentJSLocker& locker, VM& vm, Visitor& visitor)
{
CodeBlock* codeBlock = m_codeBlock.get();
codeBlock->propagateTransitions(locker, visitor);
codeBlock->determineLiveness(locker, visitor);
if (visitor.isMarked(codeBlock))
vm.executableToCodeBlockEdgesWithConstraints.remove(this);
}
template void ExecutableToCodeBlockEdge::runConstraint(const ConcurrentJSLocker&, VM&, AbstractSlotVisitor&);
template void ExecutableToCodeBlockEdge::runConstraint(const ConcurrentJSLocker&, VM&, SlotVisitor&);
} // namespace JSC
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