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Maintain only one best candidate during combineStack.

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This commit is contained in:
Daniel Kirchner 2021-08-16 17:26:24 +02:00
parent 79d39d241c
commit 1612648268
1 changed files with 9 additions and 5 deletions
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14
libyul/backends/evm/StackLayoutGenerator.cpp
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@ -496,8 +496,6 @@ Stack StackLayoutGenerator::combineStack(Stack const& _stack1, Stack const& _sta
return holds_alternative<LiteralSlot>(slot) || holds_alternative<FunctionCallReturnLabelSlot>(slot);
});
std::map<size_t, Stack> sortedCandidates;
auto evaluate = [&](Stack const& _candidate) -> size_t {
size_t numOps = 0;
Stack testStack = _candidate;
@ -518,7 +516,8 @@ Stack StackLayoutGenerator::combineStack(Stack const& _stack1, Stack const& _sta
// See https://en.wikipedia.org/wiki/Heap's_algorithm
size_t n = candidate.size();
sortedCandidates.insert(std::make_pair(evaluate(candidate), candidate));
Stack bestCandidate = candidate;
size_t bestCost = evaluate(candidate);
std::vector<size_t> c(n, 0);
size_t i = 1;
while (i < n)
@ -529,7 +528,12 @@ Stack StackLayoutGenerator::combineStack(Stack const& _stack1, Stack const& _sta
std::swap(candidate.front(), candidate[i]);
else
std::swap(candidate[c[i]], candidate[i]);
sortedCandidates.insert(std::make_pair(evaluate(candidate), candidate));
size_t cost = evaluate(candidate);
if (cost < bestCost)
{
bestCost = cost;
bestCandidate = candidate;
}
++c[i];
// Note that for a proper implementation of the Heap algorithm this would need to revert back to ``i = 1.``
// However, the incorrect implementation produces decent result and the proper version would have n!
@ -543,7 +547,7 @@ Stack StackLayoutGenerator::combineStack(Stack const& _stack1, Stack const& _sta
}
}
return commonPrefix + sortedCandidates.begin()->second;
return commonPrefix + bestCandidate;
}
Stack StackLayoutGenerator::compressStack(Stack _stack)