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Do not rematerialize recursively.

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This commit is contained in:
chriseth 2019-05-22 17:55:36 +02:00
parent a86a88f123
commit 0f146ce55a
1 changed files with 21 additions and 5 deletions
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26
libyul/optimiser/StackCompressor.cpp
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@ -48,15 +48,16 @@ class RematCandidateSelector: public DataFlowAnalyzer
public:
explicit RematCandidateSelector(Dialect const& _dialect): DataFlowAnalyzer(_dialect) {}
/// @returns a set of pairs of rematerialisation costs and variable to rematerialise.
/// @returns a set of tuples of rematerialisation costs, variable to rematerialise
/// and variables that occur in its expression.
/// Note that this set is sorted by cost.
set<pair<size_t, YulString>> candidates()
set<tuple<size_t, YulString, set<YulString>>> candidates()
{
set<pair<size_t, YulString>> cand;
set<tuple<size_t, YulString, set<YulString>>> cand;
for (auto const& codeCost: m_expressionCodeCost)
{
size_t numRef = m_numReferences[codeCost.first];
cand.emplace(make_pair(codeCost.second * numRef, codeCost.first));
cand.emplace(make_tuple(codeCost.second * numRef, codeCost.first, m_references[codeCost.first]));
}
return cand;
}
@ -123,7 +124,22 @@ void eliminateVariables(Dialect const& _dialect, ASTNode& _node, size_t _numVari
{
if (varsToEliminate.size() >= _numVariables)
break;
varsToEliminate.insert(costs.second);
// If a variable we would like to eliminate references another one
// we already selected for elimination, then stop selecting
// candidates. If we would add that variable, then the cost calculation
// for the previous variable would be off. Furthermore, we
// do not skip the variable because it would be better to properly re-compute
// the costs of all other variables instead.
bool referencesVarToEliminate = false;
for (YulString const& referencedVar: get<2>(costs))
if (varsToEliminate.count(referencedVar))
{
referencesVarToEliminate = true;
break;
}
if (referencesVarToEliminate)
break;
varsToEliminate.insert(get<1>(costs));
}
Rematerialiser::run(_dialect, _node, std::move(varsToEliminate));