diff --git a/libyul/CMakeLists.txt b/libyul/CMakeLists.txt
index 175a443a1..052aed121 100644
--- a/libyul/CMakeLists.txt
+++ b/libyul/CMakeLists.txt
@@ -56,6 +56,8 @@ add_library(yul
optimiser/BlockDeepener.h
optimiser/BlockFlattener.cpp
optimiser/BlockFlattener.h
+ optimiser/BlockHasher.cpp
+ optimiser/BlockHasher.h
optimiser/BlockClassFinder.cpp
optimiser/BlockClassFinder.h
optimiser/BlockOutliner.cpp
diff --git a/libyul/optimiser/BlockHasher.cpp b/libyul/optimiser/BlockHasher.cpp
new file mode 100644
index 000000000..4eaebab00
--- /dev/null
+++ b/libyul/optimiser/BlockHasher.cpp
@@ -0,0 +1,184 @@
+/*
+ This file is part of solidity.
+
+ solidity is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ solidity is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with solidity. If not, see .
+*/
+/**
+ * Optimiser component that calculates hash values for block prefixes.
+ */
+
+#include
+#include
+#include
+
+using namespace std;
+using namespace dev;
+using namespace yul;
+
+namespace {
+static constexpr uint64_t compileTimeLiteralHash(char const* _literal, size_t _N)
+{
+ return (_N == 0) ? 14695981039346656037u : compileTimeLiteralHash(_literal + 1, _N - 1) ^ 1099511628211u;
+}
+
+template
+static constexpr uint64_t compileTimeLiteralHash(char const (&_literal)[N])
+{
+ return compileTimeLiteralHash(_literal, N);
+}
+}
+
+BlockHasher::State BlockHasher::run(Block const& _block)
+{
+ BlockHasher::State result;
+ BlockHasher blockHasher(result);
+ blockHasher(_block);
+ return result;
+}
+
+void BlockHasher::operator()(Literal const& _literal)
+{
+ hash(compileTimeLiteralHash("Literal"));
+ hash(_literal.value.hash());
+ hash(_literal.type.hash());
+ hash(static_cast(static_cast>(_literal.kind)));
+}
+
+void BlockHasher::operator()(Identifier const& _identifier)
+{
+ hash(compileTimeLiteralHash("Identifier"));
+ auto it = m_variableReferences.find(_identifier.name);
+ if (it == m_variableReferences.end())
+ it = m_variableReferences.emplace(_identifier.name, VariableReference {
+ m_externalIdentifierCount++,
+ true
+ }).first;
+
+ if (it->second.isExternal)
+ hash(compileTimeLiteralHash("external"));
+ else
+ hash(compileTimeLiteralHash("internal"));
+ hash(it->second.id);
+}
+
+void BlockHasher::operator()(FunctionalInstruction const& _instr)
+{
+ hash(compileTimeLiteralHash("FunctionalInstruction"));
+ hash(static_cast>(_instr.instruction));
+ hash(_instr.arguments.size());
+ ASTWalker::operator()(_instr);
+}
+
+void BlockHasher::operator()(FunctionCall const& _funCall)
+{
+ hash(compileTimeLiteralHash("FunctionCall"));
+ hash(_funCall.arguments.size());
+ hash(_funCall.functionName.name.hash());
+ ASTWalker::operator()(_funCall);
+}
+
+void BlockHasher::operator()(ExpressionStatement const& _statement)
+{
+ hash(compileTimeLiteralHash("ExpressionStatement"));
+ ASTWalker::operator()(_statement);
+}
+
+void BlockHasher::operator()(Assignment const& _assignment)
+{
+ hash(compileTimeLiteralHash("Assignment"));
+ hash(_assignment.variableNames.size());
+ for (auto const& name: _assignment.variableNames)
+ (*this)(name);
+ visit(*_assignment.value);
+}
+
+void BlockHasher::operator()(VariableDeclaration const& _varDecl)
+{
+ hash(compileTimeLiteralHash("VariableDeclaration"));
+ hash(_varDecl.variables.size());
+ for (auto const& var: _varDecl.variables)
+ {
+ yulAssert(!m_variableReferences.count(var.name), "");
+ m_variableReferences[var.name] = VariableReference{
+ m_internalIdentifierCount++,
+ false
+ };
+ }
+ ASTWalker::operator()(_varDecl);
+}
+
+void BlockHasher::operator()(If const& _if)
+{
+ hash(compileTimeLiteralHash("If"));
+ ASTWalker::operator()(_if);
+}
+
+void BlockHasher::operator()(Switch const& _switch)
+{
+ hash(compileTimeLiteralHash("Switch"));
+ hash(_switch.cases.size());
+ ASTWalker::operator()(_switch);
+}
+
+void BlockHasher::operator()(FunctionDefinition const& _funDef)
+{
+ hash(compileTimeLiteralHash("FunctionDefinition"));
+ ASTWalker::operator()(_funDef);
+}
+
+void BlockHasher::operator()(ForLoop const& _loop)
+{
+ hash(compileTimeLiteralHash("ForLoop"));
+ ASTWalker::operator()(_loop);
+}
+
+void BlockHasher::operator()(Break const& _break)
+{
+ hash(compileTimeLiteralHash("Break"));
+ ASTWalker::operator()(_break);
+}
+
+void BlockHasher::operator()(Continue const& _continue)
+{
+ hash(compileTimeLiteralHash("Continue"));
+ ASTWalker::operator()(_continue);
+}
+
+
+void BlockHasher::operator()(Block const& _block)
+{
+ hash(compileTimeLiteralHash("Block"));
+ hash(_block.statements.size());
+ if (_block.statements.empty())
+ return;
+
+ BlockHasher subBlockPrefixHasher(m_state);
+ BlockPart blockPart { &_block, 0 };
+ for (auto const& statement: _block.statements)
+ {
+ subBlockPrefixHasher.visit(statement);
+ ++blockPart.length;
+ m_state.blockPrefixHashes[blockPart] = subBlockPrefixHasher.m_hash;
+ m_state.hashClasses[subBlockPrefixHasher.m_hash].emplace_back(blockPart);
+ }
+ // propagate external references in subblock
+ hash(subBlockPrefixHasher.m_hash);
+ std::vector externalReferences;
+ for (auto const& variableReference: subBlockPrefixHasher.m_variableReferences)
+ if (variableReference.second.isExternal)
+ externalReferences.emplace_back(variableReference.first);
+ hash(externalReferences.size());
+ for (auto& externalReference: externalReferences)
+ (*this)(Identifier{{}, externalReference});
+}
diff --git a/libyul/optimiser/BlockHasher.h b/libyul/optimiser/BlockHasher.h
new file mode 100644
index 000000000..ccff74e75
--- /dev/null
+++ b/libyul/optimiser/BlockHasher.h
@@ -0,0 +1,108 @@
+/*
+ This file is part of solidity.
+
+ solidity is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ solidity is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with solidity. If not, see .
+*/
+/**
+ * Optimiser component that calculates hash values for block prefixes.
+ */
+#pragma once
+
+#include
+#include
+#include
+#include
+
+namespace yul
+{
+
+struct BlockPart {
+ Block const* block;
+ size_t length;
+ bool operator<(BlockPart const& _rhs) const
+ {
+ return std::make_tuple(_rhs.length, _rhs.block) < std::make_tuple(length, block);
+ }
+};
+
+/**
+ * Optimiser component that calculates hash values for block prefixes.
+ *
+ * Prerequisite: Disambiguator
+ */
+class BlockHasher: public ASTWalker
+{
+public:
+ struct State {
+ std::map blockPrefixHashes;
+ std::map> hashClasses;
+ };
+
+ using ASTWalker::operator();
+
+ void operator()(Literal const&) override;
+ void operator()(Identifier const&) override;
+ void operator()(FunctionalInstruction const& _instr) override;
+ void operator()(FunctionCall const& _funCall) override;
+ void operator()(ExpressionStatement const& _statement) override;
+ void operator()(Assignment const& _assignment) override;
+ void operator()(VariableDeclaration const& _varDecl) override;
+ void operator()(If const& _if) override;
+ void operator()(Switch const& _switch) override;
+ void operator()(FunctionDefinition const&) override;
+ void operator()(ForLoop const&) override;
+ void operator()(Break const&) override;
+ void operator()(Continue const&) override;
+ void operator()(Block const& _block) override;
+
+ static State run(Block const& _block);
+
+private:
+ State& m_state;
+
+ BlockHasher(State& _state): m_state(_state) {}
+
+ void hash(uint8_t _value)
+ {
+ m_hash *= 1099511628211u;
+ m_hash ^= _value;
+ }
+ void hash(uint16_t _value)
+ {
+ hash(static_cast(_value & 0xFF));
+ hash(static_cast(_value >> 8));
+ }
+ void hash(uint32_t _value)
+ {
+ hash(static_cast(_value & 0xFFFF));
+ hash(static_cast(_value >> 16));
+ }
+ void hash(uint64_t _value)
+ {
+ hash(static_cast(_value & 0xFFFFFFFF));
+ hash(static_cast(_value >> 32));
+ }
+
+ uint64_t m_hash = 14695981039346656037u;
+ struct VariableReference {
+ size_t id = 0;
+ bool isExternal = false;
+ };
+ std::map m_variableReferences;
+ size_t m_externalIdentifierCount = 0;
+ size_t m_internalIdentifierCount = 0;
+};
+
+
+}