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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 "BytecodeUseDef.h"
#include "CodeBlock.h"
#include "InterpreterInlines.h"
namespace JSC {
inline bool virtualRegisterIsAlwaysLive(VirtualRegister reg)
{
return !reg.isLocal();
}
inline bool virtualRegisterThatIsNotAlwaysLiveIsLive(const FastBitVector& out, VirtualRegister reg)
{
unsigned local = reg.toLocal();
if (local >= out.numBits())
return false;
return out[local];
}
inline bool virtualRegisterIsLive(const FastBitVector& out, VirtualRegister operand)
{
return virtualRegisterIsAlwaysLive(operand) || virtualRegisterThatIsNotAlwaysLiveIsLive(out, operand);
}
inline bool isValidRegisterForLiveness(VirtualRegister operand)
{
if (operand.isConstant())
return false;
return operand.isLocal();
}
template<typename CodeBlockType, typename DefFunctor>
inline void BytecodeLivenessPropagation::stepOverBytecodeIndexDef(CodeBlockType* codeBlock, const JSInstructionStream& instructions, BytecodeGraph&, BytecodeIndex bytecodeIndex, const DefFunctor& def)
{
auto* instruction = instructions.at(bytecodeIndex).ptr();
computeDefsForBytecodeIndex(
codeBlock, instruction, bytecodeIndex.checkpoint(),
[&] (VirtualRegister operand) {
if (isValidRegisterForLiveness(operand))
def(operand.toLocal());
});
}
template<typename CodeBlockType, typename UseFunctor>
inline void BytecodeLivenessPropagation::stepOverBytecodeIndexUse(CodeBlockType* codeBlock, const JSInstructionStream& instructions, BytecodeGraph&, BytecodeIndex bytecodeIndex, const UseFunctor& use)
{
auto* instruction = instructions.at(bytecodeIndex).ptr();
computeUsesForBytecodeIndex(
codeBlock, instruction, bytecodeIndex.checkpoint(),
[&] (VirtualRegister operand) {
if (isValidRegisterForLiveness(operand))
use(operand.toLocal());
});
}
template<typename CodeBlockType, typename UseFunctor>
inline void BytecodeLivenessPropagation::stepOverBytecodeIndexUseInExceptionHandler(CodeBlockType* codeBlock, const JSInstructionStream&, BytecodeGraph& graph, BytecodeIndex bytecodeIndex, const UseFunctor& use)
{
// 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 BytecodeIndex.
if (auto* handler = codeBlock->handlerForBytecodeIndex(bytecodeIndex)) {
auto* handlerBlock = graph.findBasicBlockWithLeaderOffset(handler->target);
ASSERT(handlerBlock);
handlerBlock->in().forEachSetBit(use);
}
}
// Simplified interface to bytecode use/def, which determines defs first and then uses, and includes
// exception handlers in the uses.
template<typename CodeBlockType, typename UseFunctor, typename DefFunctor>
inline void BytecodeLivenessPropagation::stepOverBytecodeIndex(CodeBlockType* codeBlock, const JSInstructionStream& instructions, BytecodeGraph& graph, BytecodeIndex bytecodeIndex, const UseFunctor& use, const DefFunctor& def)
{
// This abstractly executes the BytecodeIndex 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).
stepOverBytecodeIndexDef(codeBlock, instructions, graph, bytecodeIndex, def);
stepOverBytecodeIndexUseInExceptionHandler(codeBlock, instructions, graph, bytecodeIndex, use);
stepOverBytecodeIndexUse(codeBlock, instructions, graph, bytecodeIndex, use);
}
template<typename CodeBlockType>
inline void BytecodeLivenessPropagation::stepOverInstruction(CodeBlockType* codeBlock, const JSInstructionStream& instructions, BytecodeGraph& graph, BytecodeIndex bytecodeIndex, FastBitVector& out)
{
auto numberOfCheckpoints = instructions.at(bytecodeIndex)->numberOfCheckpoints();
for (Checkpoint checkpoint = numberOfCheckpoints; checkpoint--;) {
stepOverBytecodeIndex(
codeBlock, instructions, graph, bytecodeIndex.withCheckpoint(checkpoint),
[&] (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 CodeBlockType, typename Instructions>
inline bool BytecodeLivenessPropagation::computeLocalLivenessForInstruction(CodeBlockType* codeBlock, const Instructions& instructions, BytecodeGraph& graph, JSBytecodeBasicBlock& block, BytecodeIndex targetIndex, FastBitVector& result)
{
ASSERT(!block.isExitBlock());
ASSERT(!block.isEntryBlock());
ASSERT_WITH_MESSAGE(!targetIndex.checkpoint(), "computeLocalLivenessForInstruction can't be used to ask questions about checkpoints");
FastBitVector out = block.out();
unsigned cursor = block.totalLength();
for (unsigned i = block.delta().size(); i--;) {
cursor -= block.delta()[i];
BytecodeIndex bytecodeIndex = BytecodeIndex(block.leaderOffset() + cursor);
if (targetIndex.offset() > bytecodeIndex.offset())
break;
stepOverInstruction(codeBlock, instructions, graph, bytecodeIndex, out);
}
return result.setAndCheck(out);
}
template<typename CodeBlockType, typename Instructions>
inline bool BytecodeLivenessPropagation::computeLocalLivenessForBlock(CodeBlockType* codeBlock, const Instructions& instructions, BytecodeGraph& graph, JSBytecodeBasicBlock& block)
{
if (block.isExitBlock() || block.isEntryBlock())
return false;
return computeLocalLivenessForInstruction(codeBlock, instructions, graph, block, BytecodeIndex(block.leaderOffset()), block.in());
}
template<typename CodeBlockType, typename Instructions>
inline FastBitVector BytecodeLivenessPropagation::getLivenessInfoAtInstruction(CodeBlockType* codeBlock, const Instructions& instructions, BytecodeGraph& graph, BytecodeIndex bytecodeIndex)
{
ASSERT_WITH_MESSAGE(!bytecodeIndex.checkpoint(), "getLivenessInfoAtInstruction can't be used to ask questions about checkpoints");
auto* block = graph.findBasicBlockForBytecodeOffset(bytecodeIndex.offset());
ASSERT(block);
ASSERT(!block->isEntryBlock());
ASSERT(!block->isExitBlock());
FastBitVector out;
out.resize(block->out().numBits());
computeLocalLivenessForInstruction(codeBlock, instructions, graph, *block, bytecodeIndex, out);
return out;
}
template<typename CodeBlockType, typename Instructions>
inline void BytecodeLivenessPropagation::runLivenessFixpoint(CodeBlockType* codeBlock, const Instructions& instructions, BytecodeGraph& graph)
{
unsigned numberOfVariables = codeBlock->numCalleeLocals();
for (auto& block : graph) {
block.in().resize(numberOfVariables);
block.out().resize(numberOfVariables);
block.in().clearAll();
block.out().clearAll();
}
bool changed;
auto& lastBlock = graph.last();
lastBlock.in().clearAll();
lastBlock.out().clearAll();
FastBitVector newOut;
newOut.resize(lastBlock.out().numBits());
do {
changed = false;
for (auto& block : graph.basicBlocksInReverseOrder()) {
newOut.clearAll();
for (unsigned blockIndex : block.successors()) {
auto& successor = graph[blockIndex];
newOut |= successor.in();
}
block.out() = newOut;
changed |= computeLocalLivenessForBlock(codeBlock, instructions, graph, block);
}
} while (changed);
}
} // namespace JSC
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