path: root/libsolidity/interface/GasEstimator.cpp

/*
    This file is part of cpp-ethereum.

    cpp-ethereum is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    cpp-ethereum is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with cpp-ethereum.  If not, see <http://www.gnu.org/licenses/>.
*/
/**
 * @author Christian <c@ethdev.com>
 * @date 2015
 * Gas consumption estimator working alongside the AST.
 */

#include "GasEstimator.h"
#include <map>
#include <functional>
#include <memory>
#include <libdevcore/SHA3.h>
#include <libevmasm/ControlFlowGraph.h>
#include <libevmasm/KnownState.h>
#include <libevmasm/PathGasMeter.h>
#include <libsolidity/ast/AST.h>
#include <libsolidity/ast/ASTVisitor.h>
#include <libsolidity/codegen/CompilerUtils.h>

using namespace std;
using namespace dev;
using namespace dev::eth;
using namespace dev::solidity;

GasEstimator::ASTGasConsumptionSelfAccumulated GasEstimator::structuralEstimation(
    AssemblyItems const& _items,
    vector<ASTNode const*> const& _ast
)
{
    solAssert(std::count(_ast.begin(), _ast.end(), nullptr) == 0, "");
    map<SourceLocation, GasConsumption> particularCosts;

    ControlFlowGraph cfg(_items);
    for (BasicBlock const& block: cfg.optimisedBlocks())
    {
        assertThrow(!!block.startState, OptimizerException, "");
        GasMeter meter(block.startState->copy());
        auto const end = _items.begin() + block.end;
        for (auto iter = _items.begin() + block.begin; iter != end; ++iter)
            particularCosts[iter->location()] += meter.estimateMax(*iter);
    }

    set<ASTNode const*> finestNodes = finestNodesAtLocation(_ast);
    ASTGasConsumptionSelfAccumulated gasCosts;
    auto onNode = [&](ASTNode const& _node)
    {
        if (!finestNodes.count(&_node))
            return true;
        gasCosts[&_node][0] = gasCosts[&_node][1] = particularCosts[_node.location()];
        return true;
    };
    auto onEdge = [&](ASTNode const& _parent, ASTNode const& _child)
    {
        gasCosts[&_parent][1] += gasCosts[&_child][1];
    };
    ASTReduce folder(onNode, onEdge);
    for (ASTNode const* ast: _ast)
        ast->accept(folder);

    return gasCosts;
}

map<ASTNode const*, GasMeter::GasConsumption> GasEstimator::breakToStatementLevel(
    ASTGasConsumptionSelfAccumulated const& _gasCosts,
    vector<ASTNode const*> const& _roots
)
{
    solAssert(std::count(_roots.begin(), _roots.end(), nullptr) == 0, "");
    // first pass: statementDepth[node] is the distance from the deepend statement to node
    // in direction of the tree root (or undefined if not possible)
    map<ASTNode const*, int> statementDepth;
    auto onNodeFirstPass = [&](ASTNode const& _node)
    {
        if (dynamic_cast<Statement const*>(&_node))
            statementDepth[&_node] = 0;
        return true;
    };
    auto onEdgeFirstPass = [&](ASTNode const& _parent, ASTNode const& _child)
    {
        if (statementDepth.count(&_child))
            statementDepth[&_parent] = max(statementDepth[&_parent], statementDepth[&_child] + 1);
    };
    ASTReduce firstPass(onNodeFirstPass, onEdgeFirstPass);
    for (ASTNode const* node: _roots)
        node->accept(firstPass);

    // we use the location of a node if
    //  - its statement depth is 0 or
    //  - its statement depth is undefined but the parent's statement depth is at least 1
    map<ASTNode const*, GasConsumption> gasCosts;
    auto onNodeSecondPass = [&](ASTNode const& _node)
    {
        return statementDepth.count(&_node);
    };
    auto onEdgeSecondPass = [&](ASTNode const& _parent, ASTNode const& _child)
    {
        bool useNode = false;
        if (statementDepth.count(&_child))
            useNode = statementDepth[&_child] == 0;
        else
            useNode = statementDepth.count(&_parent) && statementDepth.at(&_parent) > 0;
        if (useNode)
            gasCosts[&_child] = _gasCosts.at(&_child)[1];
    };
    ASTReduce secondPass(onNodeSecondPass, onEdgeSecondPass);
    for (ASTNode const* node: _roots)
        node->accept(secondPass);
    // gasCosts should only contain non-overlapping locations
    return gasCosts;
}

GasEstimator::GasConsumption GasEstimator::functionalEstimation(
    AssemblyItems const& _items,
    string const& _signature
)
{
    auto state = make_shared<KnownState>();

    if (!_signature.empty())
    {
        ExpressionClasses& classes = state->expressionClasses();
        using Id = ExpressionClasses::Id;
        using Ids = vector<Id>;
        Id hashValue = classes.find(u256(FixedHash<4>::Arith(FixedHash<4>(dev::sha3(_signature)))));
        Id calldata = classes.find(Instruction::CALLDATALOAD, Ids{classes.find(u256(0))});
        classes.forceEqual(hashValue, Instruction::DIV, Ids{
            calldata,
            classes.find(u256(1) << (8 * 28))
        });
    }

    PathGasMeter meter(_items);
    return meter.estimateMax(0, state);
}

GasEstimator::GasConsumption GasEstimator::functionalEstimation(
    AssemblyItems const& _items,
    size_t const& _offset,
    FunctionDefinition const& _function
)
{
    auto state = make_shared<KnownState>();

    unsigned parametersSize = CompilerUtils::sizeOnStack(_function.parameters());
    if (parametersSize > 16)
        return GasConsumption::infinite();

    // Store an invalid return value on the stack, so that the path estimator breaks upon reaching
    // the return jump.
    AssemblyItem invalidTag(PushTag, u256(-0x10));
    state->feedItem(invalidTag, true);
    if (parametersSize > 0)
        state->feedItem(swapInstruction(parametersSize));

    return PathGasMeter(_items).estimateMax(_offset, state);
}

set<ASTNode const*> GasEstimator::finestNodesAtLocation(
    vector<ASTNode const*> const& _roots
)
{
    map<SourceLocation, ASTNode const*> locations;
    set<ASTNode const*> nodes;
    SimpleASTVisitor visitor(function<bool(ASTNode const&)>(), [&](ASTNode const& _n)
    {
        if (!locations.count(_n.location()))
        {
            locations[_n.location()] = &_n;
            nodes.insert(&_n);
        }
    });

    for (ASTNode const* root: _roots)
        root->accept(visitor);
    return nodes;
}