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/*
* Copyright (C) 2013-2025 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 "DFGCriticalEdgeBreakingPhase.h"
#if ENABLE(DFG_JIT)
#include "DFGBasicBlockInlines.h"
#include "DFGBlockInsertionSet.h"
#include "DFGGraph.h"
#include "DFGPhase.h"
#include "JSCJSValueInlines.h"
namespace JSC { namespace DFG {
class CriticalEdgeBreakingPhase : public Phase {
public:
CriticalEdgeBreakingPhase(Graph& graph)
: Phase(graph, "critical edge breaking"_s)
, m_insertionSet(graph)
{
}
bool run()
{
Vector<BasicBlock*> newJumpPads;
for (BlockIndex blockIndex = 0; blockIndex < m_graph.numBlocks(); ++blockIndex) {
BasicBlock* block = m_graph.block(blockIndex);
if (!block)
continue;
// An edge A->B is critical if A has multiple successor and B has multiple
// predecessors. Thus we fail early if we don't have multiple successors.
if (block->numSuccessors() <= 1)
continue;
// Break critical edges by inserting a "Jump" pad block in place of each
// unique A->B critical edge.
UncheckedKeyHashMap<BasicBlock*, BasicBlock*> successorPads;
for (unsigned i = block->numSuccessors(); i--;) {
BasicBlock** successor = &block->successor(i);
if ((*successor)->predecessors.size() <= 1)
continue;
BasicBlock* pad = nullptr;
auto iter = successorPads.find(*successor);
if (iter == successorPads.end()) {
pad = m_insertionSet.insertBefore(*successor, (*successor)->executionCount);
pad->appendNode(
m_graph, SpecNone, Jump, (*successor)->at(0)->origin, OpInfo(*successor));
pad->predecessors.append(block);
(*successor)->replacePredecessor(block, pad);
successorPads.set(*successor, pad);
newJumpPads.append(pad);
} else
pad = iter->value;
*successor = pad;
}
}
bool changed = m_insertionSet.execute();
if (changed && m_graph.m_shouldFixAvailability)
performFixJumpPadAvailability(newJumpPads);
return changed;
}
// This finalizes variable availability and Phi placement for newly inserted jump pads.
// It is necessary after loop unrolling and critical edge breaking to ensure SSA and OSR correctness.
void performFixJumpPadAvailability(Vector<BasicBlock*>& pads)
{
for (BasicBlock* pad : pads) {
ASSERT(pad->isJumpPad());
BasicBlock* successor = pad->successor(0);
for (unsigned i = successor->variablesAtHead.size(); i--;) {
Node* node = successor->variablesAtHead[i];
if (!node)
continue;
VariableAccessData* variable = node->variableAccessData();
Node* phi = m_graph.addNode(Phi, node->origin, OpInfo(variable));
pad->phis.append(phi);
switch (variable->operand().kind()) {
case OperandKind::Argument: {
size_t index = variable->operand().toArgument();
pad->variablesAtHead.atFor<OperandKind::Argument>(index) = phi;
pad->variablesAtTail.atFor<OperandKind::Argument>(index) = phi;
break;
}
case OperandKind::Local: {
size_t index = variable->operand().toLocal();
pad->variablesAtHead.atFor<OperandKind::Local>(index) = phi;
pad->variablesAtTail.atFor<OperandKind::Local>(index) = phi;
break;
}
case OperandKind::Tmp: {
size_t index = variable->operand().value();
pad->variablesAtHead.atFor<OperandKind::Tmp>(index) = phi;
pad->variablesAtTail.atFor<OperandKind::Tmp>(index) = phi;
break;
}
}
}
pad->isExcludedFromFTLCodeSizeEstimation = true;
}
}
private:
BlockInsertionSet m_insertionSet;
};
bool performCriticalEdgeBreaking(Graph& graph)
{
return runPhase<CriticalEdgeBreakingPhase>(graph);
}
} } // namespace JSC::DFG
#endif // ENABLE(DFG_JIT)
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