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Simplify rematerialization candidates.

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This commit is contained in:
chriseth 2022-03-16 16:43:21 +01:00
parent af86a80536
commit a054285f31
1 changed files with 7 additions and 17 deletions
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24
libyul/optimiser/StackCompressor.cpp
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@ -61,16 +61,15 @@ public:
/// @returns a map from function name to rematerialisation costs to a vector of variables to rematerialise /// @returns a map from function name to rematerialisation costs to a vector of variables to rematerialise
/// and variables that occur in their expression. /// and variables that occur in their expression.
/// While the map is sorted by cost, the contained vectors are sorted by the order of occurrence. /// While the map is sorted by cost, the contained vectors are sorted by the order of occurrence.
map<YulString, map<size_t, vector<tuple<YulString, set<YulString>>>>> candidates() map<YulString, map<size_t, vector<YulString>>> candidates()
{ {
map<YulString, map<size_t, vector<tuple<YulString, set<YulString>>>>> cand; map<YulString, map<size_t, vector<YulString>>> cand;
for (auto const& [functionName, candidate]: m_candidates) for (auto const& [functionName, candidate]: m_candidates)
{ {
if (size_t const* cost = util::valueOrNullptr(m_expressionCodeCost, candidate)) if (size_t const* cost = util::valueOrNullptr(m_expressionCodeCost, candidate))
{ {
size_t numRef = m_numReferences[candidate]; size_t numRef = m_numReferences[candidate];
set<YulString> const* ref = references(candidate); cand[functionName][*cost * numRef].emplace_back(candidate);
cand[functionName][*cost * numRef].emplace_back(candidate, ref ? move(*ref) : set<YulString>{});
} }
} }
return cand; return cand;
@ -144,25 +143,16 @@ public:
/// Selects at most @a _numVariables among @a _candidates. /// Selects at most @a _numVariables among @a _candidates.
set<YulString> chooseVarsToEliminate( set<YulString> chooseVarsToEliminate(
map<size_t, vector<tuple<YulString, set<YulString>>>> const& _candidates, map<size_t, vector<YulString>> const& _candidates,
size_t _numVariables size_t _numVariables
) )
{ {
set<YulString> varsToEliminate; set<YulString> varsToEliminate;
for (auto&& [cost, candidates]: _candidates) for (auto&& [cost, candidates]: _candidates)
for (auto&& [candidate, references]: candidates) for (auto&& candidate: candidates)
{ {
if (varsToEliminate.size() >= _numVariables) if (varsToEliminate.size() >= _numVariables)
return varsToEliminate; return varsToEliminate;
// 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.
for (YulString const& referencedVar: references)
if (varsToEliminate.count(referencedVar))
return varsToEliminate;
varsToEliminate.insert(candidate); varsToEliminate.insert(candidate);
} }
return varsToEliminate; return varsToEliminate;
@ -177,7 +167,7 @@ void eliminateVariables(
{ {
RematCandidateSelector selector{_dialect}; RematCandidateSelector selector{_dialect};
selector(_ast); selector(_ast);
map<YulString, map<size_t, vector<tuple<YulString, set<YulString>>>>> candidates = selector.candidates(); map<YulString, map<size_t, vector<YulString>>> candidates = selector.candidates();
set<YulString> varsToEliminate; set<YulString> varsToEliminate;
for (auto const& [functionName, numVariables]: _numVariables) for (auto const& [functionName, numVariables]: _numVariables)
@ -209,7 +199,7 @@ void eliminateVariablesOptimizedCodegen(
for (auto const& [functionName, candidatesInFunction]: selector.candidates()) for (auto const& [functionName, candidatesInFunction]: selector.candidates())
for (auto [cost, candidatesWithCost]: candidatesInFunction) for (auto [cost, candidatesWithCost]: candidatesInFunction)
for (auto candidate: candidatesWithCost) for (auto candidate: candidatesWithCost)
candidates[get<0>(candidate)] = cost; candidates[candidate] = cost;
set<YulString> varsToEliminate; set<YulString> varsToEliminate;