From 83f6330ee9a6799549c554cb90c22554895e5dbf Mon Sep 17 00:00:00 2001
From: Nikola Matic <nikola.matic@ethereum.org>
Date: Wed, 22 Mar 2023 13:19:29 +0100
Subject: [PATCH] Reverse lookup optimization for DataFlowAnalyzer

---
 libyul/optimiser/DataFlowAnalyzer.cpp | 11 ++++++++---
 libyul/optimiser/DataFlowAnalyzer.h   |  2 ++
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/libyul/optimiser/DataFlowAnalyzer.cpp b/libyul/optimiser/DataFlowAnalyzer.cpp
index 81028e300..9b15d20a9 100644
--- a/libyul/optimiser/DataFlowAnalyzer.cpp
+++ b/libyul/optimiser/DataFlowAnalyzer.cpp
@@ -272,6 +272,8 @@ void DataFlowAnalyzer::handleAssignment(set<YulString> const& _variables, Expres
 	for (auto const& name: _variables)
 	{
 		m_state.references[name] = referencedVariables;
+		for (auto&& referencedVariable: referencedVariables)
+			m_state.references_reverse_lookup[referencedVariable].insert(name);
 		if (!_isDeclaration)
 		{
 			// assignment to slot denoted by "name"
@@ -316,6 +318,8 @@ void DataFlowAnalyzer::popScope()
 	for (auto const& name: m_variableScopes.back().variables)
 	{
 		m_state.value.erase(name);
+		for (auto&& ref: m_state.references[name])
+			m_state.references_reverse_lookup.erase(ref);
 		m_state.references.erase(name);
 	}
 	m_variableScopes.pop_back();
@@ -353,14 +357,15 @@ void DataFlowAnalyzer::clearValues(set<YulString> _variables)
 
 	// Also clear variables that reference variables to be cleared.
 	for (auto const& variableToClear: _variables)
-		for (auto const& [ref, names]: m_state.references)
-			if (names.count(variableToClear))
-				_variables.emplace(ref);
+		if (m_state.references_reverse_lookup.count(variableToClear))
+			_variables += m_state.references_reverse_lookup[variableToClear];
 
 	// Clear the value and update the reference relation.
 	for (auto const& name: _variables)
 	{
 		m_state.value.erase(name);
+		for (auto&& ref: m_state.references[name])
+			m_state.references_reverse_lookup.erase(ref);
 		m_state.references.erase(name);
 	}
 }
diff --git a/libyul/optimiser/DataFlowAnalyzer.h b/libyul/optimiser/DataFlowAnalyzer.h
index b449357e6..77862eb45 100644
--- a/libyul/optimiser/DataFlowAnalyzer.h
+++ b/libyul/optimiser/DataFlowAnalyzer.h
@@ -181,6 +181,8 @@ private:
 		std::map<YulString, AssignedValue> value;
 		/// m_references[a].contains(b) <=> the current expression assigned to a references b
 		std::unordered_map<YulString, std::set<YulString>> references;
+		/// Reverse lookup for above m_references map
+		std::unordered_map<YulString, std::set<YulString>> references_reverse_lookup;
 
 		Environment environment;
 	};