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/*
* Copyright (C) 2013-2017 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. AND ITS CONTRIBUTORS ``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 ITS 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.
*/
#pragma once
#include "BytecodeGraph.h"
#include "BytecodeLivenessAnalysis.h"
#include "CodeBlock.h"
#include "InterpreterInlines.h"
#include "Operations.h"
namespace JSC {
inline bool operandIsAlwaysLive(int operand)
{
return !VirtualRegister(operand).isLocal();
}
inline bool operandThatIsNotAlwaysLiveIsLive(const FastBitVector& out, int operand)
{
unsigned local = VirtualRegister(operand).toLocal();
if (local >= out.numBits())
return false;
return out[local];
}
inline bool operandIsLive(const FastBitVector& out, int operand)
{
return operandIsAlwaysLive(operand) || operandThatIsNotAlwaysLiveIsLive(out, operand);
}
inline bool isValidRegisterForLiveness(int operand)
{
VirtualRegister virtualReg(operand);
if (virtualReg.isConstant())
return false;
return virtualReg.isLocal();
}
// Simplified interface to bytecode use/def, which determines defs first and then uses, and includes
// exception handlers in the uses.
template<typename DerivedAnalysis>
template<typename Graph, typename UseFunctor, typename DefFunctor>
inline void BytecodeLivenessPropagation<DerivedAnalysis>::stepOverInstruction(Graph& graph, unsigned bytecodeOffset, FastBitVector& out, const UseFunctor& use, const DefFunctor& def)
{
// This abstractly execute the instruction in reverse. Instructions logically first use operands and
// then define operands. This logical ordering is necessary for operations that use and def the same
// operand, like:
//
// op_add loc1, loc1, loc2
//
// The use of loc1 happens before the def of loc1. That's a semantic requirement since the add
// operation cannot travel forward in time to read the value that it will produce after reading that
// value. Since we are executing in reverse, this means that we must do defs before uses (reverse of
// uses before defs).
//
// Since this is a liveness analysis, this ordering ends up being particularly important: if we did
// uses before defs, then the add operation above would appear to not have loc1 live, since we'd
// first add it to the out set (the use), and then we'd remove it (the def).
auto* codeBlock = graph.codeBlock();
auto* instructionsBegin = graph.instructions().begin();
auto* instruction = &instructionsBegin[bytecodeOffset];
OpcodeID opcodeID = Interpreter::getOpcodeID(*instruction);
static_cast<DerivedAnalysis*>(this)->computeDefsForBytecodeOffset(
codeBlock, opcodeID, instruction, out,
[&] (typename Graph::CodeBlock*, typename Graph::Instruction*, OpcodeID, int operand) {
if (isValidRegisterForLiveness(operand))
def(VirtualRegister(operand).toLocal());
});
static_cast<DerivedAnalysis*>(this)->computeUsesForBytecodeOffset(
codeBlock, opcodeID, instruction, out,
[&] (typename Graph::CodeBlock*, typename Graph::Instruction*, OpcodeID, int operand) {
if (isValidRegisterForLiveness(operand))
use(VirtualRegister(operand).toLocal());
});
// If we have an exception handler, we want the live-in variables of the
// exception handler block to be included in the live-in of this particular bytecode.
if (auto* handler = codeBlock->handlerForBytecodeOffset(bytecodeOffset)) {
BytecodeBasicBlock* handlerBlock = graph.findBasicBlockWithLeaderOffset(handler->target);
ASSERT(handlerBlock);
handlerBlock->in().forEachSetBit(use);
}
}
template<typename DerivedAnalysis>
template<typename Graph>
inline void BytecodeLivenessPropagation<DerivedAnalysis>::stepOverInstruction(Graph& graph, unsigned bytecodeOffset, FastBitVector& out)
{
stepOverInstruction(
graph, bytecodeOffset, out,
[&] (unsigned bitIndex) {
// This is the use functor, so we set the bit.
out[bitIndex] = true;
},
[&] (unsigned bitIndex) {
// This is the def functor, so we clear the bit.
out[bitIndex] = false;
});
}
template<typename DerivedAnalysis>
template<typename Graph>
inline bool BytecodeLivenessPropagation<DerivedAnalysis>::computeLocalLivenessForBytecodeOffset(Graph& graph, BytecodeBasicBlock* block, unsigned targetOffset, FastBitVector& result)
{
ASSERT(!block->isExitBlock());
ASSERT(!block->isEntryBlock());
FastBitVector out = block->out();
for (int i = block->offsets().size() - 1; i >= 0; i--) {
unsigned bytecodeOffset = block->offsets()[i];
if (targetOffset > bytecodeOffset)
break;
stepOverInstruction(graph, bytecodeOffset, out);
}
return result.setAndCheck(out);
}
template<typename DerivedAnalysis>
template<typename Graph>
inline bool BytecodeLivenessPropagation<DerivedAnalysis>::computeLocalLivenessForBlock(Graph& graph, BytecodeBasicBlock* block)
{
if (block->isExitBlock() || block->isEntryBlock())
return false;
return computeLocalLivenessForBytecodeOffset(graph, block, block->leaderOffset(), block->in());
}
template<typename DerivedAnalysis>
template<typename Graph>
inline FastBitVector BytecodeLivenessPropagation<DerivedAnalysis>::getLivenessInfoAtBytecodeOffset(Graph& graph, unsigned bytecodeOffset)
{
BytecodeBasicBlock* block = graph.findBasicBlockForBytecodeOffset(bytecodeOffset);
ASSERT(block);
ASSERT(!block->isEntryBlock());
ASSERT(!block->isExitBlock());
FastBitVector out;
out.resize(block->out().numBits());
computeLocalLivenessForBytecodeOffset(graph, block, bytecodeOffset, out);
return out;
}
template<typename DerivedAnalysis>
template<typename Graph>
inline void BytecodeLivenessPropagation<DerivedAnalysis>::runLivenessFixpoint(Graph& graph)
{
auto* codeBlock = graph.codeBlock();
unsigned numberOfVariables = codeBlock->numCalleeLocals();
for (BytecodeBasicBlock* block : graph) {
block->in().resize(numberOfVariables);
block->out().resize(numberOfVariables);
block->in().clearAll();
block->out().clearAll();
}
bool changed;
BytecodeBasicBlock* lastBlock = graph.last();
lastBlock->in().clearAll();
lastBlock->out().clearAll();
FastBitVector newOut;
newOut.resize(lastBlock->out().numBits());
do {
changed = false;
for (std::unique_ptr<BytecodeBasicBlock>& block : graph.basicBlocksInReverseOrder()) {
newOut.clearAll();
for (BytecodeBasicBlock* successor : block->successors())
newOut |= successor->in();
block->out() = newOut;
changed |= computeLocalLivenessForBlock(graph, block.get());
}
} while (changed);
}
} // namespace JSC
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