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/*
* Copyright (C) 2013, 2015 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 "DFGLivenessAnalysisPhase.h"
#if ENABLE(DFG_JIT)
#include "DFGBasicBlockInlines.h"
#include "DFGGraph.h"
#include "DFGInsertionSet.h"
#include "DFGPhase.h"
#include "JSCInlines.h"
namespace JSC { namespace DFG {
class LivenessAnalysisPhase : public Phase {
public:
LivenessAnalysisPhase(Graph& graph)
: Phase(graph, "liveness analysis")
{
}
bool run()
{
ASSERT(m_graph.m_form == SSA);
// Liveness is a backwards analysis; the roots are the blocks that
// end in a terminal (Return/Throw/ThrowReferenceError). For now, we
// use a fixpoint formulation since liveness is a rapid analysis with
// convergence guaranteed after O(connectivity).
// Start by assuming that everything is dead.
for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
BasicBlock* block = m_graph.block(blockIndex);
if (!block)
continue;
block->ssa->liveAtTailIsDirty = true;
block->ssa->liveAtHead.clear();
block->ssa->liveAtTail.clear();
}
do {
m_changed = false;
for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;)
process(blockIndex);
} while (m_changed);
if (!m_graph.block(0)->ssa->liveAtHead.isEmpty()) {
DFG_CRASH(
m_graph, nullptr,
toCString(
"Bad liveness analysis result: live at root is not empty: ",
nodeListDump(m_graph.block(0)->ssa->liveAtHead)).data());
}
return true;
}
private:
void process(BlockIndex blockIndex)
{
BasicBlock* block = m_graph.block(blockIndex);
if (!block)
return;
if (!block->ssa->liveAtTailIsDirty)
return;
block->ssa->liveAtTailIsDirty = false;
m_live = block->ssa->liveAtTail;
for (unsigned nodeIndex = block->size(); nodeIndex--;) {
Node* node = block->at(nodeIndex);
// Given an Upsilon:
//
// n: Upsilon(@x, ^p)
//
// We say that it def's @p and @n and uses @x.
//
// Given a Phi:
//
// p: Phi()
//
// We say nothing. It's neither a use nor a def.
//
// Given a node:
//
// n: Thingy(@a, @b, @c)
//
// We say that it def's @n and uses @a, @b, @c.
switch (node->op()) {
case Upsilon: {
Node* phi = node->phi();
m_live.remove(phi);
m_live.remove(node);
m_live.add(node->child1().node());
break;
}
case Phi: {
break;
}
default:
m_live.remove(node);
DFG_NODE_DO_TO_CHILDREN(m_graph, node, addChildUse);
break;
}
}
for (Node* node : m_live) {
if (!block->ssa->liveAtHead.contains(node)) {
m_changed = true;
for (unsigned i = block->predecessors.size(); i--;) {
BasicBlock* predecessor = block->predecessors[i];
if (predecessor->ssa->liveAtTail.add(node).isNewEntry)
predecessor->ssa->liveAtTailIsDirty = true;
}
}
}
block->ssa->liveAtHead = WTFMove(m_live);
}
void addChildUse(Node*, Edge& edge)
{
addChildUse(edge);
}
void addChildUse(Edge& edge)
{
edge.setKillStatus(m_live.add(edge.node()).isNewEntry ? DoesKill : DoesNotKill);
}
bool m_changed;
HashSet<Node*> m_live;
};
bool performLivenessAnalysis(Graph& graph)
{
SamplingRegion samplingRegion("DFG Liveness Analysis Phase");
return runPhase<LivenessAnalysisPhase>(graph);
}
} } // namespace JSC::DFG
#endif // ENABLE(DFG_JIT)
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