Merge pull request #4083 from ethereum/variable_stack_slot

[BREAKING] Allocate local variables according to their scope

6 files changed, 129 insertions, 42 deletions

diff --git a/libsolidity/codegen/CompilerContext.cpp b/libsolidity/codegen/CompilerContext.cpp
index a35eea73..3b1b4ec0 100644
--- a/libsolidity/codegen/CompilerContext.cpp
+++ b/libsolidity/codegen/CompilerContext.cpp
@@ -127,10 +127,14 @@ void CompilerContext::addVariable(VariableDeclaration const& _declaration,
 								  unsigned _offsetToCurrent)
 {
 	solAssert(m_asm->deposit() >= 0 && unsigned(m_asm->deposit()) >= _offsetToCurrent, "");
+	unsigned sizeOnStack = _declaration.annotation().type->sizeOnStack();
+	// Variables should not have stack size other than [1, 2],
+	// but that might change when new types are introduced.
+	solAssert(sizeOnStack == 1 || sizeOnStack == 2, "");
 	m_localVariables[&_declaration].push_back(unsigned(m_asm->deposit()) - _offsetToCurrent);
 }
 
-void CompilerContext::removeVariable(VariableDeclaration const& _declaration)
+void CompilerContext::removeVariable(Declaration const& _declaration)
 {
 	solAssert(m_localVariables.count(&_declaration) && !m_localVariables[&_declaration].empty(), "");
 	m_localVariables[&_declaration].pop_back();
@@ -138,6 +142,25 @@ void CompilerContext::removeVariable(VariableDeclaration const& _declaration)
 		m_localVariables.erase(&_declaration);
 }
 
+void CompilerContext::removeVariablesAboveStackHeight(unsigned _stackHeight)
+{
+	vector<Declaration const*> toRemove;
+	for (auto _var: m_localVariables)
+	{
+		solAssert(!_var.second.empty(), "");
+		solAssert(_var.second.back() <= stackHeight(), "");
+		if (_var.second.back() >= _stackHeight)
+			toRemove.push_back(_var.first);
+	}
+	for (auto _var: toRemove)
+		removeVariable(*_var);
+}
+
+unsigned CompilerContext::numberOfLocalVariables() const
+{
+	return m_localVariables.size();
+}
+
 eth::Assembly const& CompilerContext::compiledContract(const ContractDefinition& _contract) const
 {
 	auto ret = m_compiledContracts.find(&_contract);
diff --git a/libsolidity/codegen/CompilerContext.h b/libsolidity/codegen/CompilerContext.h
index 5776b5d1..3f357821 100644
--- a/libsolidity/codegen/CompilerContext.h
+++ b/libsolidity/codegen/CompilerContext.h
@@ -71,7 +71,11 @@ public:
 
 	void addStateVariable(VariableDeclaration const& _declaration, u256 const& _storageOffset, unsigned _byteOffset);
 	void addVariable(VariableDeclaration const& _declaration, unsigned _offsetToCurrent = 0);
-	void removeVariable(VariableDeclaration const& _declaration);
+	void removeVariable(Declaration const& _declaration);
+	/// Removes all local variables currently allocated above _stackHeight.
+	void removeVariablesAboveStackHeight(unsigned _stackHeight);
+	/// Returns the number of currently allocated local variables.
+	unsigned numberOfLocalVariables() const;
 
 	void setCompiledContracts(std::map<ContractDefinition const*, eth::Assembly const*> const& _contracts) { m_compiledContracts = _contracts; }
 	eth::Assembly const& compiledContract(ContractDefinition const& _contract) const;
diff --git a/libsolidity/codegen/CompilerUtils.cpp b/libsolidity/codegen/CompilerUtils.cpp
index 2e335ca5..2d81a106 100644
--- a/libsolidity/codegen/CompilerUtils.cpp
+++ b/libsolidity/codegen/CompilerUtils.cpp
@@ -1170,6 +1170,15 @@ void CompilerUtils::popStackSlots(size_t _amount)
 		m_context << Instruction::POP;
 }
 
+void CompilerUtils::popAndJump(unsigned _toHeight, eth::AssemblyItem const& _jumpTo)
+{
+	solAssert(m_context.stackHeight() >= _toHeight, "");
+	unsigned amount = m_context.stackHeight() - _toHeight;
+	popStackSlots(amount);
+	m_context.appendJumpTo(_jumpTo);
+	m_context.adjustStackOffset(amount);
+}
+
 unsigned CompilerUtils::sizeOnStack(vector<shared_ptr<Type const>> const& _variableTypes)
 {
 	unsigned size = 0;
diff --git a/libsolidity/codegen/CompilerUtils.h b/libsolidity/codegen/CompilerUtils.h
index 0ff3ad7c..26df4765 100644
--- a/libsolidity/codegen/CompilerUtils.h
+++ b/libsolidity/codegen/CompilerUtils.h
@@ -241,6 +241,10 @@ public:
 	void popStackElement(Type const& _type);
 	/// Removes element from the top of the stack _amount times.
 	void popStackSlots(size_t _amount);
+	/// Pops slots from the stack such that its height is _toHeight.
+	/// Adds jump to _jumpTo.
+	/// Readjusts the stack offset to the original value.
+	void popAndJump(unsigned _toHeight, eth::AssemblyItem const& _jumpTo);
 
 	template <class T>
 	static unsigned sizeOnStack(std::vector<T> const& _variables);
diff --git a/libsolidity/codegen/ContractCompiler.cpp b/libsolidity/codegen/ContractCompiler.cpp
index 81aba21e..93f698bc 100644
--- a/libsolidity/codegen/ContractCompiler.cpp
+++ b/libsolidity/codegen/ContractCompiler.cpp
@@ -427,7 +427,7 @@ bool ContractCompiler::visit(FunctionDefinition const& _function)
 	m_context.startFunction(_function);
 
 	// stack upon entry: [return address] [arg0] [arg1] ... [argn]
-	// reserve additional slots: [retarg0] ... [retargm] [localvar0] ... [localvarp]
+	// reserve additional slots: [retarg0] ... [retargm]
 
 	unsigned parametersSize = CompilerUtils::sizeOnStack(_function.parameters());
 	if (!_function.isConstructor())
@@ -441,8 +441,6 @@ bool ContractCompiler::visit(FunctionDefinition const& _function)
 
 	for (ASTPointer<VariableDeclaration const> const& variable: _function.returnParameters())
 		appendStackVariableInitialisation(*variable);
-	for (VariableDeclaration const* localVariable: _function.localVariables())
-		appendStackVariableInitialisation(*localVariable);
 
 	if (_function.isConstructor())
 		if (auto c = m_context.nextConstructor(dynamic_cast<ContractDefinition const&>(*_function.scope())))
@@ -451,12 +449,11 @@ bool ContractCompiler::visit(FunctionDefinition const& _function)
 	solAssert(m_returnTags.empty(), "");
 	m_breakTags.clear();
 	m_continueTags.clear();
-	m_stackCleanupForReturn = 0;
 	m_currentFunction = &_function;
 	m_modifierDepth = -1;
+	m_scopeStackHeight.clear();
 
 	appendModifierOrFunctionCode();
-
 	solAssert(m_returnTags.empty(), "");
 
 	// Now we need to re-shuffle the stack. For this we keep a record of the stack layout
@@ -467,14 +464,12 @@ bool ContractCompiler::visit(FunctionDefinition const& _function)
 
 	unsigned const c_argumentsSize = CompilerUtils::sizeOnStack(_function.parameters());
 	unsigned const c_returnValuesSize = CompilerUtils::sizeOnStack(_function.returnParameters());
-	unsigned const c_localVariablesSize = CompilerUtils::sizeOnStack(_function.localVariables());
 
 	vector<int> stackLayout;
 	stackLayout.push_back(c_returnValuesSize); // target of return address
 	stackLayout += vector<int>(c_argumentsSize, -1); // discard all arguments
 	for (unsigned i = 0; i < c_returnValuesSize; ++i)
 		stackLayout.push_back(i);
-	stackLayout += vector<int>(c_localVariablesSize, -1);
 
 	if (stackLayout.size() > 17)
 		BOOST_THROW_EXCEPTION(
@@ -493,18 +488,23 @@ bool ContractCompiler::visit(FunctionDefinition const& _function)
 			m_context << swapInstruction(stackLayout.size() - stackLayout.back() - 1);
 			swap(stackLayout[stackLayout.back()], stackLayout.back());
 		}
-	//@todo assert that everything is in place now
+	for (int i = 0; i < int(stackLayout.size()); ++i)
+		if (stackLayout[i] != i)
+			solAssert(false, "Invalid stack layout on cleanup.");
 
 	for (ASTPointer<VariableDeclaration const> const& variable: _function.parameters() + _function.returnParameters())
 		m_context.removeVariable(*variable);
-	for (VariableDeclaration const* localVariable: _function.localVariables())
-		m_context.removeVariable(*localVariable);
 
 	m_context.adjustStackOffset(-(int)c_returnValuesSize);
 
 	/// The constructor and the fallback function doesn't to jump out.
-	if (!_function.isConstructor() && !_function.isFallback())
-		m_context.appendJump(eth::AssemblyItem::JumpType::OutOfFunction);
+	if (!_function.isConstructor())
+	{
+		solAssert(m_context.numberOfLocalVariables() == 0, "");
+		if (!_function.isFallback())
+			m_context.appendJump(eth::AssemblyItem::JumpType::OutOfFunction);
+	}
+
 	return false;
 }
 
@@ -669,14 +669,14 @@ bool ContractCompiler::visit(WhileStatement const& _whileStatement)
 
 	eth::AssemblyItem loopStart = m_context.newTag();
 	eth::AssemblyItem loopEnd = m_context.newTag();
-	m_breakTags.push_back(loopEnd);
+	m_breakTags.push_back({loopEnd, m_context.stackHeight()});
 
 	m_context << loopStart;
 
 	if (_whileStatement.isDoWhile())
 	{
 		eth::AssemblyItem condition = m_context.newTag();
-		m_continueTags.push_back(condition);
+		m_continueTags.push_back({condition, m_context.stackHeight()});
 
 		_whileStatement.body().accept(*this);
 
@@ -687,7 +687,7 @@ bool ContractCompiler::visit(WhileStatement const& _whileStatement)
 	}
 	else
 	{
-		m_continueTags.push_back(loopStart);
+		m_continueTags.push_back({loopStart, m_context.stackHeight()});
 		compileExpression(_whileStatement.condition());
 		m_context << Instruction::ISZERO;
 		m_context.appendConditionalJumpTo(loopEnd);
@@ -712,12 +712,14 @@ bool ContractCompiler::visit(ForStatement const& _forStatement)
 	eth::AssemblyItem loopStart = m_context.newTag();
 	eth::AssemblyItem loopEnd = m_context.newTag();
 	eth::AssemblyItem loopNext = m_context.newTag();
-	m_continueTags.push_back(loopNext);
-	m_breakTags.push_back(loopEnd);
+
+	storeStackHeight(&_forStatement);
 
 	if (_forStatement.initializationExpression())
 		_forStatement.initializationExpression()->accept(*this);
 
+	m_breakTags.push_back({loopEnd, m_context.stackHeight()});
+	m_continueTags.push_back({loopNext, m_context.stackHeight()});
 	m_context << loopStart;
 
 	// if there is no terminating condition in for, default is to always be true
@@ -737,11 +739,16 @@ bool ContractCompiler::visit(ForStatement const& _forStatement)
 		_forStatement.loopExpression()->accept(*this);
 
 	m_context.appendJumpTo(loopStart);
+
 	m_context << loopEnd;
 
 	m_continueTags.pop_back();
 	m_breakTags.pop_back();
 
+	// For the case where no break/return is executed:
+	// loop initialization variables have to be freed
+	popScopedVariables(&_forStatement);
+
 	checker.check();
 	return false;
 }
@@ -750,7 +757,7 @@ bool ContractCompiler::visit(Continue const& _continueStatement)
 {
 	CompilerContext::LocationSetter locationSetter(m_context, _continueStatement);
 	solAssert(!m_continueTags.empty(), "");
-	m_context.appendJumpTo(m_continueTags.back());
+	CompilerUtils(m_context).popAndJump(m_continueTags.back().second, m_continueTags.back().first);
 	return false;
 }
 
@@ -758,7 +765,7 @@ bool ContractCompiler::visit(Break const& _breakStatement)
 {
 	CompilerContext::LocationSetter locationSetter(m_context, _breakStatement);
 	solAssert(!m_breakTags.empty(), "");
-	m_context.appendJumpTo(m_breakTags.back());
+	CompilerUtils(m_context).popAndJump(m_breakTags.back().second, m_breakTags.back().first);
 	return false;
 }
 
@@ -784,10 +791,8 @@ bool ContractCompiler::visit(Return const& _return)
 		for (auto const& retVariable: boost::adaptors::reverse(returnParameters))
 			CompilerUtils(m_context).moveToStackVariable(*retVariable);
 	}
-	for (unsigned i = 0; i < m_stackCleanupForReturn; ++i)
-		m_context << Instruction::POP;
-	m_context.appendJumpTo(m_returnTags.back());
-	m_context.adjustStackOffset(m_stackCleanupForReturn);
+
+	CompilerUtils(m_context).popAndJump(m_returnTags.back().second, m_returnTags.back().first);
 	return false;
 }
 
@@ -810,8 +815,15 @@ bool ContractCompiler::visit(EmitStatement const& _emit)
 
 bool ContractCompiler::visit(VariableDeclarationStatement const& _variableDeclarationStatement)
 {
-	StackHeightChecker checker(m_context);
 	CompilerContext::LocationSetter locationSetter(m_context, _variableDeclarationStatement);
+
+	// Local variable slots are reserved when their declaration is visited,
+	// and freed in the end of their scope.
+	for (auto _decl: _variableDeclarationStatement.declarations())
+		if (_decl)
+			appendStackVariableInitialisation(*_decl);
+
+	StackHeightChecker checker(m_context);
 	if (Expression const* expression = _variableDeclarationStatement.initialValue())
 	{
 		CompilerUtils utils(m_context);
@@ -861,6 +873,18 @@ bool ContractCompiler::visit(PlaceholderStatement const& _placeholderStatement)
 	return true;
 }
 
+bool ContractCompiler::visit(Block const& _block)
+{
+	storeStackHeight(&_block);
+	return true;
+}
+
+void ContractCompiler::endVisit(Block const& _block)
+{
+	// Frees local variables declared in the scope of this block.
+	popScopedVariables(&_block);
+}
+
 void ContractCompiler::appendMissingFunctions()
 {
 	while (Declaration const* function = m_context.nextFunctionToCompile())
@@ -916,27 +940,19 @@ void ContractCompiler::appendModifierOrFunctionCode()
 					modifier.parameters()[i]->annotation().type
 				);
 			}
-			for (VariableDeclaration const* localVariable: modifier.localVariables())
-			{
-				addedVariables.push_back(localVariable);
-				appendStackVariableInitialisation(*localVariable);
-			}
 
-			stackSurplus =
-				CompilerUtils::sizeOnStack(modifier.parameters()) +
-				CompilerUtils::sizeOnStack(modifier.localVariables());
+			stackSurplus = CompilerUtils::sizeOnStack(modifier.parameters());
 			codeBlock = &modifier.body();
 		}
 	}
 
 	if (codeBlock)
 	{
-		m_returnTags.push_back(m_context.newTag());
-
+		m_returnTags.push_back({m_context.newTag(), m_context.stackHeight()});
 		codeBlock->accept(*this);
 
 		solAssert(!m_returnTags.empty(), "");
-		m_context << m_returnTags.back();
+		m_context << m_returnTags.back().first;
 		m_returnTags.pop_back();
 
 		CompilerUtils(m_context).popStackSlots(stackSurplus);
@@ -983,3 +999,20 @@ eth::AssemblyPointer ContractCompiler::cloneRuntime() const
 	a << u256(0x20) << u256(0) << Instruction::RETURN;
 	return make_shared<eth::Assembly>(a);
 }
+
+void ContractCompiler::popScopedVariables(ASTNode const* _node)
+{
+	unsigned blockHeight = m_scopeStackHeight.at(m_modifierDepth).at(_node);
+	m_context.removeVariablesAboveStackHeight(blockHeight);
+	solAssert(m_context.stackHeight() >= blockHeight, "");
+	unsigned stackDiff = m_context.stackHeight() - blockHeight;
+	CompilerUtils(m_context).popStackSlots(stackDiff);
+	m_scopeStackHeight[m_modifierDepth].erase(_node);
+	if (m_scopeStackHeight[m_modifierDepth].size() == 0)
+		m_scopeStackHeight.erase(m_modifierDepth);
+}
+
+void ContractCompiler::storeStackHeight(ASTNode const* _node)
+{
+	m_scopeStackHeight[m_modifierDepth][_node] = m_context.stackHeight();
+}
diff --git a/libsolidity/codegen/ContractCompiler.h b/libsolidity/codegen/ContractCompiler.h
index 02a3452f..8516ec2c 100644
--- a/libsolidity/codegen/ContractCompiler.h
+++ b/libsolidity/codegen/ContractCompiler.h
@@ -109,6 +109,8 @@ private:
 	virtual bool visit(VariableDeclarationStatement const& _variableDeclarationStatement) override;
 	virtual bool visit(ExpressionStatement const& _expressionStatement) override;
 	virtual bool visit(PlaceholderStatement const&) override;
+	virtual bool visit(Block const& _block) override;
+	virtual void endVisit(Block const& _block) override;
 
 	/// Repeatedly visits all function which are referenced but which are not compiled yet.
 	void appendMissingFunctions();
@@ -123,19 +125,31 @@ private:
 	/// @returns the runtime assembly for clone contracts.
 	eth::AssemblyPointer cloneRuntime() const;
 
+	/// Frees the variables of a certain scope (to be used when leaving).
+	void popScopedVariables(ASTNode const* _node);
+
+	/// Sets the stack height for the visited loop.
+	void storeStackHeight(ASTNode const* _node);
+
 	bool const m_optimise;
 	/// Pointer to the runtime compiler in case this is a creation compiler.
 	ContractCompiler* m_runtimeCompiler = nullptr;
 	CompilerContext& m_context;
-	std::vector<eth::AssemblyItem> m_breakTags; ///< tag to jump to for a "break" statement
-	std::vector<eth::AssemblyItem> m_continueTags; ///< tag to jump to for a "continue" statement
-	/// Tag to jump to for a "return" statement, needs to be stacked because of modifiers.
-	std::vector<eth::AssemblyItem> m_returnTags;
+	/// Tag to jump to for a "break" statement and the stack height after freeing the local loop variables.
+	std::vector<std::pair<eth::AssemblyItem, unsigned>> m_breakTags;
+	/// Tag to jump to for a "continue" statement and the stack height after freeing the local loop variables.
+	std::vector<std::pair<eth::AssemblyItem, unsigned>> m_continueTags;
+	/// Tag to jump to for a "return" statement and the stack height after freeing the local function or modifier variables.
+	/// Needs to be stacked because of modifiers.
+	std::vector<std::pair<eth::AssemblyItem, unsigned>> m_returnTags;
 	unsigned m_modifierDepth = 0;
 	FunctionDefinition const* m_currentFunction = nullptr;
-	unsigned m_stackCleanupForReturn = 0; ///< this number of stack elements need to be removed before jump to m_returnTag
+
 	// arguments for base constructors, filled in derived-to-base order
 	std::map<FunctionDefinition const*, ASTNode const*> const* m_baseArguments;
+
+	/// Stores the variables that were declared inside a specific scope, for each modifier depth.
+	std::map<unsigned, std::map<ASTNode const*, unsigned>> m_scopeStackHeight;
 };
 
 }