solidity/libyul/optimiser/LoopInvariantCodeMotion.cpp

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/*
This file is part of solidity.
solidity 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.
solidity 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 solidity. If not, see <http://www.gnu.org/licenses/>.
*/
#include <libyul/optimiser/LoopInvariantCodeMotion.h>
#include <libyul/optimiser/CallGraphGenerator.h>
#include <libyul/optimiser/NameCollector.h>
#include <libyul/optimiser/Semantics.h>
#include <libyul/optimiser/SSAValueTracker.h>
#include <libyul/AsmData.h>
#include <libsolutil/CommonData.h>
#include <utility>
using namespace std;
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using namespace solidity;
using namespace solidity::yul;
void LoopInvariantCodeMotion::run(OptimiserStepContext& _context, Block& _ast)
{
map<YulString, SideEffects> functionSideEffects =
SideEffectsPropagator::sideEffects(_context.dialect, CallGraphGenerator::callGraph(_ast));
set<YulString> ssaVars = SSAValueTracker::ssaVariables(_ast);
LoopInvariantCodeMotion{_context.dialect, ssaVars, functionSideEffects}(_ast);
}
void LoopInvariantCodeMotion::operator()(Block& _block)
{
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util::iterateReplacing(
_block.statements,
[&](Statement& _s) -> optional<vector<Statement>>
{
visit(_s);
if (holds_alternative<ForLoop>(_s))
return rewriteLoop(get<ForLoop>(_s));
else
return {};
}
);
}
bool LoopInvariantCodeMotion::canBePromoted(
VariableDeclaration const& _varDecl,
set<YulString> const& _varsDefinedInCurrentScope
) const
{
// A declaration can be promoted iff
// 1. Its LHS is a SSA variable
// 2. Its RHS only references SSA variables declared outside of the current scope
// 3. Its RHS is movable
for (auto const& var: _varDecl.variables)
if (!m_ssaVariables.count(var.name))
return false;
if (_varDecl.value)
{
for (auto const& ref: ReferencesCounter::countReferences(*_varDecl.value, ReferencesCounter::OnlyVariables))
if (_varsDefinedInCurrentScope.count(ref.first) || !m_ssaVariables.count(ref.first))
return false;
if (!SideEffectsCollector{m_dialect, *_varDecl.value, &m_functionSideEffects}.movable())
return false;
}
return true;
}
optional<vector<Statement>> LoopInvariantCodeMotion::rewriteLoop(ForLoop& _for)
{
assertThrow(_for.pre.statements.empty(), OptimizerException, "");
vector<Statement> replacement;
for (Block* block: {&_for.post, &_for.body})
{
set<YulString> varsDefinedInScope;
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util::iterateReplacing(
block->statements,
[&](Statement& _s) -> optional<vector<Statement>>
{
if (holds_alternative<VariableDeclaration>(_s))
{
VariableDeclaration const& varDecl = std::get<VariableDeclaration>(_s);
if (canBePromoted(varDecl, varsDefinedInScope))
{
replacement.emplace_back(std::move(_s));
// Do not add the variables declared here to varsDefinedInScope because we are moving them.
return vector<Statement>{};
}
for (auto const& var: varDecl.variables)
varsDefinedInScope.insert(var.name);
}
return {};
}
);
}
if (replacement.empty())
return {};
else
{
replacement.emplace_back(std::move(_for));
return { std::move(replacement) };
}
}