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Merge pull request #9427 from ethereum/recursiveFunctionDetection

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Extract recursive function detection from Semantics into the CallGraph.
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chriseth 2020-07-15 20:31:48 +02:00 committed by GitHub
commit 59c6a1f57b
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3 changed files with 46 additions and 21 deletions
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41
libyul/optimiser/CallGraphGenerator.cpp
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@ -30,6 +30,47 @@ using namespace solidity;
using namespace solidity::yul;
using namespace solidity::util;
namespace
{
// TODO: This algorithm is non-optimal.
struct CallGraphCycleFinder
{
CallGraph const& callGraph;
set<YulString> containedInCycle{};
set<YulString> visited{};
vector<YulString> currentPath{};
void visit(YulString _function)
{
if (visited.count(_function))
return;
if (
auto it = find(currentPath.begin(), currentPath.end(), _function);
it != currentPath.end()
)
containedInCycle.insert(it, currentPath.end());
else
{
currentPath.emplace_back(_function);
if (callGraph.functionCalls.count(_function))
for (auto const& child: callGraph.functionCalls.at(_function))
visit(child);
currentPath.pop_back();
visited.insert(_function);
}
}
};
}
set<YulString> CallGraph::recursiveFunctions() const
{
CallGraphCycleFinder cycleFinder{*this};
// Visiting the root only is not enough, since there may be disconnected recursive functions.
for (auto const& call: functionCalls)
cycleFinder.visit(call.first);
return cycleFinder.containedInCycle;
}
CallGraph CallGraphGenerator::callGraph(Block const& _ast)
{
CallGraphGenerator gen;

4
libyul/optimiser/CallGraphGenerator.h
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@ -35,6 +35,10 @@ struct CallGraph
{
std::map<YulString, std::set<YulString>> functionCalls;
std::set<YulString> functionsWithLoops;
/// @returns the set of functions contained in cycles in the call graph, i.e.
/// functions that are part of a (mutual) recursion.
/// Note that this does not include functions that merely call recursive functions.
std::set<YulString> recursiveFunctions() const;
};
/**

22
libyul/optimiser/Semantics.cpp
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@ -102,33 +102,13 @@ map<YulString, SideEffects> SideEffectsPropagator::sideEffects(
// is actually a bit different from "not movable".
map<YulString, SideEffects> ret;
for (auto const& function: _directCallGraph.functionsWithLoops)
for (auto const& function: _directCallGraph.functionsWithLoops + _directCallGraph.recursiveFunctions())
{
ret[function].movable = false;
ret[function].sideEffectFree = false;
ret[function].sideEffectFreeIfNoMSize = false;
}
// Detect recursive functions.
for (auto const& call: _directCallGraph.functionCalls)
{
// TODO we could shortcut the search as soon as we find a
// function that has as bad side-effects as we can
// ever achieve via recursion.
auto search = [&](YulString const& _functionName, util::CycleDetector<YulString>& _cycleDetector, size_t) {
for (auto const& callee: _directCallGraph.functionCalls.at(_functionName))
if (!_dialect.builtin(callee))
if (_cycleDetector.run(callee))
return;
};
if (util::CycleDetector<YulString>(search).run(call.first))
{
ret[call.first].movable = false;
ret[call.first].sideEffectFree = false;
ret[call.first].sideEffectFreeIfNoMSize = false;
}
}
for (auto const& call: _directCallGraph.functionCalls)
{
YulString funName = call.first;