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Change RematCandidateSelector to not depend on variable name sorting.

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This commit is contained in:
Daniel Kirchner 2021-09-08 13:50:36 +02:00
parent d512f7a4fd
commit c499f27a63
2 changed files with 58 additions and 44 deletions
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80
libyul/optimiser/StackCompressor.cpp
View File

@ -31,6 +31,8 @@
#include <libyul/AST.h>
#include <libsolutil/CommonData.h>
using namespace std;
using namespace solidity;
using namespace solidity::yul;
@ -47,16 +49,19 @@ class RematCandidateSelector: public DataFlowAnalyzer
public:
explicit RematCandidateSelector(Dialect const& _dialect): DataFlowAnalyzer(_dialect) {}
/// @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<tuple<size_t, YulString, set<YulString>>> candidates()
/// @returns a map from rematerialisation costs to a vector of variables to rematerialise
/// and variables that occur in their expression.
/// While the map is sorted by cost, the contained vectors are sorted by the order of occurrence.
map<size_t, vector<tuple<YulString, set<YulString>>>> candidates()
{
set<tuple<size_t, YulString, set<YulString>>> cand;
for (auto const& codeCost: m_expressionCodeCost)
map<size_t, vector<tuple<YulString, set<YulString>>>> cand;
for (auto const& candidate: m_candidates)
{
size_t numRef = m_numReferences[codeCost.first];
cand.emplace(make_tuple(codeCost.second * numRef, codeCost.first, m_references[codeCost.first]));
if (size_t const* cost = util::valueOrNullptr(m_expressionCodeCost, candidate))
{
size_t numRef = m_numReferences[candidate];
cand[*cost * numRef].emplace_back(candidate, m_references[candidate]);
}
}
return cand;
}
@ -69,7 +74,11 @@ public:
{
YulString varName = _varDecl.variables.front().name;
if (m_value.count(varName))
{
yulAssert(!m_expressionCodeCost.count(varName), "");
m_candidates.emplace_back(varName);
m_expressionCodeCost[varName] = CodeCost::codeCost(m_dialect, *m_value[varName].value);
}
}
}
@ -105,12 +114,40 @@ public:
m_expressionCodeCost.erase(_variable);
}
/// All candidate variables in order of occurrence.
vector<YulString> m_candidates;
/// Candidate variables and the code cost of their value.
map<YulString, size_t> m_expressionCodeCost;
/// Number of references to each candidate variable.
map<YulString, size_t> m_numReferences;
};
/// Selects at most @a _numVariables among @a _candidates.
set<YulString> chooseVarsToEliminate(
map<size_t, vector<tuple<YulString, set<YulString>>>> const& _candidates,
size_t _numVariables
)
{
set<YulString> varsToEliminate;
for (auto&& [cost, candidates]: _candidates)
for (auto&& [candidate, references]: candidates)
{
if (varsToEliminate.size() >= _numVariables)
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);
}
return varsToEliminate;
}
template <typename ASTNode>
void eliminateVariables(
Dialect const& _dialect,
@ -121,32 +158,7 @@ void eliminateVariables(
{
RematCandidateSelector selector{_dialect};
selector(_node);
// Select at most _numVariables
set<YulString> varsToEliminate;
for (auto const& costs: selector.candidates())
{
if (varsToEliminate.size() >= _numVariables)
break;
// 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));
Rematerialiser::run(_dialect, _node, chooseVarsToEliminate(selector.candidates(), _numVariables));
UnusedPruner::runUntilStabilised(_dialect, _node, _allowMSizeOptimization);
}

22
test/libyul/yulOptimizerTests/fullSuite/aztec.yul
View File

@ -284,15 +284,17 @@
// let _5 := 0x40
// calldatacopy(0xe0, add(_3, 164), _5)
// calldatacopy(0x20, add(_3, 100), _5)
// mstore(0x120, sub(_2, c))
// mstore(0x60, k)
// let _6 := 0x120
// mstore(_6, sub(_2, c))
// let _7 := 0x60
// mstore(_7, k)
// mstore(0xc0, a)
// let result := call(gas(), 7, 0, 0xe0, 0x60, 0x1a0, _5)
// let result_1 := and(result, call(gas(), 7, 0, 0x20, 0x60, 0x120, _5))
// let _6 := 0x160
// let result_2 := and(result_1, call(gas(), 7, 0, 0x80, 0x60, _6, _5))
// let result_3 := and(result_2, call(gas(), 6, 0, 0x120, 0x80, _6, _5))
// result := and(result_3, call(gas(), 6, 0, _6, 0x80, b, _5))
// let result := call(gas(), 7, 0, 0xe0, _7, 0x1a0, _5)
// let result_1 := and(result, call(gas(), 7, 0, 0x20, _7, _6, _5))
// let _8 := 0x160
// let result_2 := and(result_1, call(gas(), 7, 0, 0x80, _7, _8, _5))
// let result_3 := and(result_2, call(gas(), 6, 0, _6, 0x80, _8, _5))
// result := and(result_3, call(gas(), 6, 0, _8, 0x80, b, _5))
// if eq(i, m)
// {
// mstore(0x260, mload(0x20))
@ -302,8 +304,8 @@
// }
// if gt(i, m)
// {
// mstore(0x60, c)
// let result_4 := and(result, call(gas(), 7, 0, 0x20, 0x60, 0x220, _5))
// mstore(_7, c)
// let result_4 := and(result, call(gas(), 7, 0, 0x20, _7, 0x220, _5))
// let result_5 := and(result_4, call(gas(), 6, 0, 0x220, 0x80, 0x260, _5))
// result := and(result_5, call(gas(), 6, 0, 0x1a0, 0x80, 0x1e0, _5))
// }