Refactored local stack

[#81180320]

libevmjit/BasicBlock.cpp

@@ -1,8 +1,11 @@
 
 #include "BasicBlock.h"
 
+#include <boost/lexical_cast.hpp>
+
 #include <llvm/IR/Function.h>
 #include <llvm/IR/Instructions.h>
+#include <llvm/IR/IRBuilder.h>
 
 #include "Type.h"
 
@@ -15,65 +18,211 @@ namespace jit
 
 const char* BasicBlock::NamePrefix = "Instr.";
 
-BasicBlock::BasicBlock(ProgramCounter _beginInstIdx, ProgramCounter _endInstIdx, llvm::Function* _mainFunc) :
+BasicBlock::BasicBlock(ProgramCounter _beginInstIdx, ProgramCounter _endInstIdx, llvm::Function* _mainFunc, llvm::IRBuilder<>& _builder) :
 	m_beginInstIdx(_beginInstIdx),
 	m_endInstIdx(_endInstIdx),
 	m_llvmBB(llvm::BasicBlock::Create(_mainFunc->getContext(), {NamePrefix, std::to_string(_beginInstIdx)}, _mainFunc)),
-	m_stack(m_llvmBB)
+	m_stack(_builder)
 {}
 
-BasicBlock::BasicBlock(std::string _name, llvm::Function* _mainFunc) :
+BasicBlock::BasicBlock(std::string _name, llvm::Function* _mainFunc, llvm::IRBuilder<>& _builder) :
 	m_beginInstIdx(0),
 	m_endInstIdx(0),
 	m_llvmBB(llvm::BasicBlock::Create(_mainFunc->getContext(), _name, _mainFunc)),
-	m_stack(m_llvmBB)
+	m_stack(_builder)
 {}
 
+BasicBlock::LocalStack::LocalStack(llvm::IRBuilder<>& _builder) :
+	m_builder(_builder),
+	m_initialStack(),
+	m_currentStack(),
+	m_tosOffset(0)
+{}
 
 void BasicBlock::LocalStack::push(llvm::Value* _value)
 {
-	assert(_value->getType() == Type::i256);
+	m_currentStack.push_back(_value);
-	m_backend.push_back(_value);
+	m_tosOffset += 1;
 }
 
 llvm::Value* BasicBlock::LocalStack::pop()
 {
-	auto top = get(0);
+	auto result = get(0);
-	m_backend.pop_back();
+
-	return top;
+	if (m_currentStack.size() > 0)
+		m_currentStack.pop_back();
+
+	m_tosOffset -= 1;
+	return result;
+}
+
+/**
+ *  Pushes a copy of _index-th element (tos is 0-th elem).
+ */
+void BasicBlock::LocalStack::dup(size_t _index)
+{
+	auto val = get(_index);
+	push(val);
+}
+
+/**
+ *  Swaps tos with _index-th element (tos is 0-th elem).
+ *  _index must be > 0.
+ */
+void BasicBlock::LocalStack::swap(size_t _index)
+{
+	assert(_index > 0);
+	auto val = get(_index);
+	auto tos = get(0);
+	set(_index, tos);
+	set(0, val);
+}
+
+void BasicBlock::LocalStack::synchronize(Stack& _evmStack)
+{
+	auto blockTerminator = m_builder.GetInsertBlock()->getTerminator();
+	assert(blockTerminator != nullptr);
+	m_builder.SetInsertPoint(blockTerminator);
+
+	auto currIter = m_currentStack.begin();
+	auto endIter = m_currentStack.end();
+
+	// Update (emit set()) changed values
+	for (int idx = m_currentStack.size() - 1 - m_tosOffset;
+		 currIter < endIter && idx >= 0;
+		 ++currIter, --idx)
+	{
+		assert(static_cast<size_t>(idx) < m_initialStack.size());
+		if (*currIter != m_initialStack[idx]) // value needs update
+			_evmStack.set(static_cast<size_t>(idx), *currIter);
+	}
+
+	if (m_tosOffset < 0)
+	{
+		// Pop values
+		_evmStack.pop(static_cast<size_t>(-m_tosOffset));
+	}
+
+	// Push new values
+	for ( ; currIter < endIter; ++currIter)
+	{
+		assert(*currIter != nullptr);
+		_evmStack.push(*currIter);
+	}
+
+	// Emit get() for all (used) values from the initial stack
+	for (size_t idx = 0; idx < m_initialStack.size(); ++idx)
+	{
+		auto val = m_initialStack[idx];
+		if (val == nullptr)
+			continue;
+
+		assert(llvm::isa<llvm::PHINode>(val));
+		llvm::PHINode* phi = llvm::cast<llvm::PHINode>(val);
+		if (! phi->use_empty())
+		{
+			// Insert call to get() just before the PHI node and replace
+			// the uses of PHI with the uses of this new instruction.
+			m_builder.SetInsertPoint(phi);
+			auto newVal = _evmStack.get(idx);
+			phi->replaceAllUsesWith(newVal);
+		}
+		phi->eraseFromParent();
+	}
+
+	// Reset the stack
+	m_initialStack.erase(m_initialStack.begin(), m_initialStack.end());
+	m_currentStack.erase(m_currentStack.begin(), m_currentStack.end());
+	m_tosOffset = 0;
+}
+
+std::vector<llvm::Value*>::iterator BasicBlock::LocalStack::getItemIterator(size_t _index)
+{
+	if (_index < m_currentStack.size())
+		return m_currentStack.end() - _index - 1;
+
+	// Need to map more elements from the EVM stack
+	auto nNewItems = 1 + _index - m_currentStack.size();
+	m_currentStack.insert(m_currentStack.begin(), nNewItems, nullptr);
+
+	return m_currentStack.end() - _index - 1;
 }
 
 llvm::Value* BasicBlock::LocalStack::get(size_t _index)
 {
-	if (_index >= m_backend.size())
+	auto itemIter = getItemIterator(_index);
+
+	if (*itemIter == nullptr)
 	{
-		// Create PHI node for missing values
+		// Need to fetch a new item from the EVM stack
-		auto nMissingVals = _index - m_backend.size() + 1;
+		assert(static_cast<int>(_index) >= m_tosOffset);
-		m_backend.insert(m_backend.begin(), nMissingVals, nullptr);
+		size_t initialIdx = _index - m_tosOffset;
-		for (decltype(nMissingVals) i = 0; i < nMissingVals; ++i)
+		if (initialIdx >= m_initialStack.size())
 		{
-			m_backend[nMissingVals - 1 - i] = m_llvmBB->empty() ?
+			auto nNewItems = 1 + initialIdx - m_initialStack.size();
-				llvm::PHINode::Create(Type::i256, 0, {}, m_llvmBB) :
+			m_initialStack.insert(m_initialStack.end(), nNewItems, nullptr);
-				llvm::PHINode::Create(Type::i256, 0, {}, m_llvmBB->getFirstNonPHI());
-			m_numRequiredStackItems += 1;
 		}
+
+		assert(m_initialStack[initialIdx] == nullptr);
+		// Create a dummy value.
+		std::string name = "get_" + boost::lexical_cast<std::string>(_index);
+		m_initialStack[initialIdx] = m_builder.CreatePHI(Type::i256, 0, name);
+		*itemIter = m_initialStack[initialIdx];
 	}
 
-	return *(m_backend.rbegin() + _index);
+	return *itemIter;
 }
 
-void BasicBlock::LocalStack::dup(size_t _index)
+void BasicBlock::LocalStack::set(size_t _index, llvm::Value* _word)
 {
-	m_backend.push_back(get(_index));
+	auto itemIter = getItemIterator(_index);
+	*itemIter = _word;
 }
 
-void BasicBlock::LocalStack::swap(size_t _index)
+
+void BasicBlock::dump()
+{
+	std::cerr << "Initial stack:\n";
+	for (auto val : m_stack.m_initialStack)
 	{
-	assert(_index != 0);
+		if (val == nullptr)
-	get(_index); // Create PHI nodes
+			std::cerr << "  ?\n";
-	std::swap(*m_backend.rbegin(), *(m_backend.rbegin() + _index));
+		else if (llvm::isa<llvm::Instruction>(val))
+			val->dump();
+		else
+		{
+			std::cerr << "  ";
+			val->dump();
+		}
+	}
+	std::cerr << "  ...\n";
+
+    std::cerr << "Instructions:\n";
+	for (auto ins = m_llvmBB->begin(); ins != m_llvmBB->end(); ++ins)
+		ins->dump();
+
+	std::cerr << "Current stack (offset = "
+			  << m_stack.m_tosOffset << "):\n";
+
+	for (auto val = m_stack.m_currentStack.rbegin(); val != m_stack.m_currentStack.rend(); ++val)
+	{
+		if (*val == nullptr)
+			std::cerr << "  ?\n";
+		else if (llvm::isa<llvm::Instruction>(*val))
+			(*val)->dump();
+		else
+		{
+			std::cerr << "  ";
+			(*val)->dump();
+		}
+
+	}
+	std::cerr << "  ...\n----------------------------------------\n";
 }
 
+
+
+
 }
 }
 }

libevmjit/BasicBlock.h

@@ -1,8 +1,11 @@
+#pragma once
 
 #include <vector>
 
 #include <llvm/IR/BasicBlock.h>
 
+#include "Stack.h"
+
 namespace dev
 {
 namespace eth
@@ -18,49 +21,72 @@ public:
 	class LocalStack
 	{
 	public:
+
 		/// Pushes value on stack
 		void push(llvm::Value* _value);
 
 		/// Pops and returns top value
 		llvm::Value* pop();
 
-		/// Gets _index'th value from top (counting from 0)
+		/// Duplicates _index'th value on stack
-		llvm::Value* get(size_t _index);
-
-		/// Duplicates _index'th value on stack.
 		void dup(size_t _index);
 
 		/// Swaps _index'th value on stack with a value on stack top.
-		/// @param _index Index of value to be swaped. Cannot be 0.
+		/// @param _index Index of value to be swaped. Must be > 0.
 		void swap(size_t _index);
 
-		/// Size of the stack
+		/// Synchronize current local stack with the EVM stack.
-		size_t size() const { return m_backend.size(); }
+		void synchronize(Stack& _evmStack);
-
-		size_t initialSize() const { return m_numRequiredStackItems; }
 
 	private:
-		// LocalStack(llvm::BasicBlock* _llvmBB) : m_llvmBB(_llvmBB) {}
+
-		LocalStack(llvm::BasicBlock* _llvmBB) : m_llvmBB(_llvmBB), m_numRequiredStackItems(0) {}
+		LocalStack(llvm::IRBuilder<>& _builder);
 		LocalStack(LocalStack const&) = delete;
 		void operator=(LocalStack const&) = delete;
 		friend BasicBlock;
 
+		/// Gets _index'th value from top (counting from 0)
+		llvm::Value* get(size_t _index);
+
+		/// Sets _index'th value from top (counting from 0)
+		void set(size_t _index, llvm::Value* _value);
+
+		std::vector<llvm::Value*>::iterator getItemIterator(size_t _index);
+
 	private:
-		std::vector<llvm::Value*> m_backend;
 
-		/** Basic block into which phi nodes are inserted */
+		llvm::IRBuilder<>& m_builder;
-		llvm::BasicBlock* m_llvmBB;
+
+		/**
+		 *  This stack contains LLVM values that correspond to items found at
+		 *  the EVM stack when the current basic block starts executing.
+		 *  Location 0 corresponds to the top of the EVM stack, location 1 is
+		 *  the item below the top and so on. The stack grows as the code
+		 *  accesses more items on the EVM stack but once a value is put on
+		 *  the stack, it will never be replaced.
+		 */
+		std::vector<llvm::Value*> m_initialStack;
+
+		/**
+		 *  This stack tracks the contents of the EVM stack as the current basic
+		 *  block executes. It may grow on both sides, as the code pushes items on
+		 *  top of the stack or changes existing items.
+		 */
+		std::vector<llvm::Value*> m_currentStack;
+
+		/**
+		 *  How many items higher is the current stack than the initial one.
+		 *  May be negative.
+		 */
+		int m_tosOffset;
 
-		/** Number of items required on the EVM stack at the beginning of the block */
-		size_t m_numRequiredStackItems;
 	};
 
 	/// Basic block name prefix. The rest is beging instruction index.
 	static const char* NamePrefix;
 
-	explicit BasicBlock(ProgramCounter _beginInstIdx, ProgramCounter _endInstIdx, llvm::Function* _mainFunc);
+	explicit BasicBlock(ProgramCounter _beginInstIdx, ProgramCounter _endInstIdx, llvm::Function* _mainFunc, llvm::IRBuilder<>& _builder);
-	explicit BasicBlock(std::string _name, llvm::Function* _mainFunc);
+	explicit BasicBlock(std::string _name, llvm::Function* _mainFunc, llvm::IRBuilder<>& _builder);
 
 	BasicBlock(const BasicBlock&) = delete;
 	void operator=(const BasicBlock&) = delete;
@@ -68,11 +94,15 @@ public:
 	operator llvm::BasicBlock*() { return m_llvmBB; }
 	llvm::BasicBlock* llvm() { return m_llvmBB; }
 
-	LocalStack& getStack() { return m_stack; }
-
 	ProgramCounter begin() { return m_beginInstIdx; }
 	ProgramCounter end() { return m_endInstIdx; }
 
+	LocalStack& localStack() { return m_stack; }
+
+	/// Prints local stack and block instructions to stderr.
+	/// Useful for calling in a debugger session.
+	void dump();
+
 private:
 	ProgramCounter const m_beginInstIdx;
 	ProgramCounter const m_endInstIdx;

libevmjit/Compiler.cpp

@@ -123,12 +123,12 @@ void Compiler::createBasicBlocks(bytesConstRef bytecode)
 		auto beginInstIdx = *it;
 		++it;
 		auto endInstIdx = it != splitPoints.cend() ? *it : bytecode.size();
-		basicBlocks.emplace(std::piecewise_construct, std::forward_as_tuple(beginInstIdx), std::forward_as_tuple(beginInstIdx, endInstIdx, m_mainFunc));
+		basicBlocks.emplace(std::piecewise_construct, std::forward_as_tuple(beginInstIdx), std::forward_as_tuple(beginInstIdx, endInstIdx, m_mainFunc, m_builder));
 	}
 
 	m_stopBB = llvm::BasicBlock::Create(m_mainFunc->getContext(), "Stop", m_mainFunc);
-	m_badJumpBlock = std::make_unique<BasicBlock>("BadJumpBlock", m_mainFunc);
+	m_badJumpBlock = std::make_unique<BasicBlock>("BadJumpBlock", m_mainFunc, m_builder);
-	m_jumpTableBlock = std::make_unique<BasicBlock>("JumpTableBlock", m_mainFunc);
+	m_jumpTableBlock = std::make_unique<BasicBlock>("JumpTableBlock", m_mainFunc, m_builder);
 
 	for (auto it = directJumpTargets.cbegin(); it != directJumpTargets.cend(); ++it)
 	{
@@ -186,6 +186,9 @@ std::unique_ptr<llvm::Module> Compiler::compile(bytesConstRef bytecode)
 		++iterCopy;
 		auto nextBasicBlock = (iterCopy != basicBlocks.end()) ? iterCopy->second.llvm() : nullptr;
 		compileBasicBlock(basicBlock, bytecode, memory, ext, gasMeter, nextBasicBlock);
+		if (getenv("EVMCC_DEBUG_BLOCKS"))
+			basicBlock.dump();
+		basicBlock.localStack().synchronize(stack);
 	}
 
 	// Code for special blocks:
@@ -201,9 +204,9 @@ std::unique_ptr<llvm::Module> Compiler::compile(bytesConstRef bytecode)
 	m_builder.SetInsertPoint(m_jumpTableBlock->llvm());
 	if (m_indirectJumpTargets.size() > 0)
 	{
-		auto& stack = m_jumpTableBlock->getStack();
+		// auto& stack = m_jumpTableBlock->getStack();
 
-		auto dest = stack.pop();
+		auto dest = m_jumpTableBlock->localStack().pop(); //m_jumpTableBlock->localGet(0); // stack.pop();
 		auto switchInstr = 	m_builder.CreateSwitch(dest, m_badJumpBlock->llvm(),
 		                   	                     m_indirectJumpTargets.size());
 		for (auto it = m_indirectJumpTargets.cbegin(); it != m_indirectJumpTargets.cend(); ++it)
@@ -218,7 +221,8 @@ std::unique_ptr<llvm::Module> Compiler::compile(bytesConstRef bytecode)
 		m_builder.CreateBr(m_badJumpBlock->llvm());
 	}
 
-	linkBasicBlocks(stack);
+	m_jumpTableBlock->localStack().synchronize(stack);
+	linkBasicBlocks();
 
 	return module;
 }
@@ -226,8 +230,8 @@ std::unique_ptr<llvm::Module> Compiler::compile(bytesConstRef bytecode)
 
 void Compiler::compileBasicBlock(BasicBlock& basicBlock, bytesConstRef bytecode, Memory& memory, Ext& ext, GasMeter& gasMeter, llvm::BasicBlock* nextBasicBlock)
 {
-	auto& stack = basicBlock.getStack();
 	m_builder.SetInsertPoint(basicBlock.llvm());
+	auto& stack = basicBlock.localStack();
 
 	for (auto currentPC = basicBlock.begin(); currentPC != basicBlock.end(); ++currentPC)
 	{
@@ -589,8 +593,6 @@ void Compiler::compileBasicBlock(BasicBlock& basicBlock, bytesConstRef bytecode,
 				}
 				else
 				{
-					// FIXME: this get(0) is a temporary workaround to get some of the jump tests running.
-					stack.get(0);
 					m_builder.CreateBr(m_jumpTableBlock->llvm());
 				}
 			}
@@ -873,7 +875,7 @@ void Compiler::compileBasicBlock(BasicBlock& basicBlock, bytesConstRef bytecode,
 }
 
 
-void Compiler::linkBasicBlocks(Stack& stack)
+void Compiler::linkBasicBlocks() // Stack& stack)
 {
 	// Remove dead basic blocks
 	auto sthErased = false;
@@ -902,13 +904,14 @@ void Compiler::linkBasicBlocks(Stack& stack)
 		m_jumpTableBlock.reset();
 	}
 
-
+/*
 	struct BBInfo
 	{
 		BasicBlock& bblock;
 		std::vector<BBInfo*> predecessors;
 		size_t inputItems;
 		size_t outputItems;
+		std::vector<llvm::PHINode*> phisToRewrite;
 
 		BBInfo(BasicBlock& _bblock)
 			: bblock(_bblock),
@@ -978,7 +981,8 @@ void Compiler::linkBasicBlocks(Stack& stack)
 		}
 	}
 
-	std::map<llvm::Instruction*, llvm::Value*> phiReplacements;
+	// std::map<llvm::Instruction*, llvm::Value*> phiReplacements;
+	// std::vector<llvm::Instruction*> phiNodesToRewrite;
 
 	// Propagate values between blocks.
 	for (auto& pair : cfg)
@@ -1001,13 +1005,14 @@ void Compiler::linkBasicBlocks(Stack& stack)
 		}
 
 		// Turn the remaining phi nodes into stack.pop's.
-		m_builder.SetInsertPoint(llbb, llvm::BasicBlock::iterator(llbb->getFirstNonPHI()));
+		// m_builder.SetInsertPoint(llbb, llvm::BasicBlock::iterator(llbb->getFirstNonPHI()));
 		for (; llvm::isa<llvm::PHINode>(*instrIter); ++instrIter)
 		{
 			auto phi = llvm::cast<llvm::PHINode>(instrIter);
-			auto value = stack.popWord();
+			// auto value = stack.popWord();
 			// Don't delete the phi node yet. It may still be stored in a local stack of some block.
-			phiReplacements[phi] = value;
+			// phiReplacements[phi] = value;
+			bbInfo.phisToRewrite.push_back(phi);
 		}
 
 		// Emit stack push's at the end of the block, just before the terminator;
@@ -1018,11 +1023,33 @@ void Compiler::linkBasicBlocks(Stack& stack)
 			stack.pushWord(bblock.getStack().get(localStackSize - 1 - i));
 	}
 
-	for (auto& entry : phiReplacements)
+	for (auto& entry : cfg)
+	{
+		// Where was the last stack.pop() inserted
+		auto lastPopIt = entry.first->begin();
+
+		for (auto phi : entry.second.phisToRewrite)
+		{
+			// Insert stack.pop() before the first use of phi,
+			// then replace all uses of phi with the popped val.
+
+			if (phi->use_begin() == phi->use_end())
+			{
+				// For a phi with no uses, insert pop just after the previous one
+			}
+			std::cout << "*** PHI node " << phi->getName().str() << " has no uses!\n";
+		}
+		else
 		{
-		entry.first->replaceAllUsesWith(entry.second);
+			assert(llvm::isa<llvm::Instruction>(phi->use_begin()->getUser()));
-		entry.first->eraseFromParent();
+
+			m_builder.SetInsertPoint(*phi->use_begin());
+			auto popVal = stack.popWord();
+			phi->replaceAllUsesWith(popVal);
+			phi->eraseFromParent();
+		}
 	}
+	*/
 }
 
 void Compiler::dumpBasicBlockGraph(std::ostream& out)
@@ -1030,7 +1057,7 @@ void Compiler::dumpBasicBlockGraph(std::ostream& out)
 	out << "digraph BB {\n"
 	    << "  node [shape=record];\n"
 	    << "  entry [share=record, label=\"entry block\"];\n";
-
+/*
 	std::vector<BasicBlock*> blocks;
 	for (auto& pair : this->basicBlocks)
 		blocks.push_back(&pair.second);
@@ -1076,6 +1103,7 @@ void Compiler::dumpBasicBlockGraph(std::ostream& out)
 	}
 
 	out << "}\n";
+	*/
 }
 
 }

libevmjit/Compiler.h

@@ -33,7 +33,7 @@ private:
 
 	void compileBasicBlock(BasicBlock& basicBlock, bytesConstRef bytecode, class Memory& memory, class Ext& ext, class GasMeter& gasMeter, llvm::BasicBlock* nextBasicBlock);
 
-	void linkBasicBlocks(class Stack& stack);
+	void linkBasicBlocks(); //class Stack& stack);
 
 
 	llvm::IRBuilder<> m_builder;

libevmjit/ExecutionEngine.cpp

@@ -19,6 +19,7 @@
 
 #include "Runtime.h"
 #include "Memory.h"
+#include "Stack.h"
 #include "Type.h"
 
 namespace dev
@@ -35,7 +36,6 @@ ExecutionEngine::ExecutionEngine()
 
 extern "C" { EXPORT std::jmp_buf* rt_jmpBuf; }
 
-
 int ExecutionEngine::run(std::unique_ptr<llvm::Module> _module, u256& _gas, ExtVMFace* _ext)
 {
 	auto module = _module.get(); // Keep ownership of the module in _module
@@ -117,6 +117,8 @@ int ExecutionEngine::run(std::unique_ptr<llvm::Module> _module, u256& _gas, ExtV
 	// Return remaining gas
 	_gas = returnCode == ReturnCode::OutOfGas ? 0 : Runtime::getGas();
 
+	std::cout << "Max stack size: " << Stack::maxStackSize << std::endl;
+
 	if (returnCode == ReturnCode::Return)
 	{
 		returnData = Memory::getReturnData().toVector(); // TODO: It might be better to place is in Runtime interface
@@ -128,6 +130,7 @@ int ExecutionEngine::run(std::unique_ptr<llvm::Module> _module, u256& _gas, ExtV
 	}
 
 	std::cout << "RETURN CODE: " << (int)returnCode << std::endl;
+
 	return static_cast<int>(returnCode);
 }
 

libevmjit/Stack.cpp

@@ -17,34 +17,48 @@ namespace jit
 Stack::Stack(llvm::IRBuilder<>& _builder)
 	: CompilerHelper(_builder)
 {
-	auto i256Ty = m_builder.getIntNTy(256);
+	m_arg = m_builder.CreateAlloca(Type::i256, nullptr, "stack.arg");
-	auto i256PtrTy = i256Ty->getPointerTo();
-
-	m_arg = m_builder.CreateAlloca(i256Ty, nullptr, "stack.retVal");
 
 	using namespace llvm;
 	using Linkage = GlobalValue::LinkageTypes;
 
 	auto module = getModule();
-	m_push = Function::Create(FunctionType::get(m_builder.getVoidTy(), i256PtrTy, false), Linkage::ExternalLinkage, "stack_push", module);
+	m_push = Function::Create(FunctionType::get(m_builder.getVoidTy(), Type::WordPtr, false), Linkage::ExternalLinkage, "stack_push", module);
-	m_pop = Function::Create(FunctionType::get(m_builder.getVoidTy(), i256PtrTy, false), Linkage::ExternalLinkage, "stack_pop", module);
+	m_pop = Function::Create(FunctionType::get(m_builder.getVoidTy(), Type::Size, false), Linkage::ExternalLinkage, "stack_pop", module);
+	llvm::Type* getSetArgTypes[] = {Type::Size, Type::WordPtr};
+	m_get = Function::Create(FunctionType::get(m_builder.getVoidTy(), ArrayRef<llvm::Type*>(getSetArgTypes), false), Linkage::ExternalLinkage, "stack_get", module);
+	m_set = Function::Create(FunctionType::get(m_builder.getVoidTy(), ArrayRef<llvm::Type*>(getSetArgTypes), false), Linkage::ExternalLinkage, "stack_set", module);
 }
 
 Stack::~Stack()
 {}
 
-llvm::Instruction* Stack::popWord()
+llvm::Value* Stack::get(size_t _index)
 {
-	m_builder.CreateCall(m_pop, m_arg);
+	m_builder.CreateCall2(m_get, llvm::ConstantInt::get(Type::Size, _index, false), m_arg);
 	return m_builder.CreateLoad(m_arg);
 }
 
-void Stack::pushWord(llvm::Value* _word)
+void Stack::set(size_t _index, llvm::Value* _value)
+{
+	m_builder.CreateStore(_value, m_arg);
+	m_builder.CreateCall2(m_set, llvm::ConstantInt::get(Type::Size, _index, false), m_arg);
+}
+
+void Stack::pop(size_t _count)
 {
-	m_builder.CreateStore(_word, m_arg);
+	m_builder.CreateCall(m_pop, llvm::ConstantInt::get(Type::Size, _count, false));
+}
+
+void Stack::push(llvm::Value* _value)
+{
+	m_builder.CreateStore(_value, m_arg);
 	m_builder.CreateCall(m_push, m_arg);
 }
 
+
+size_t Stack::maxStackSize = 0;
+
 }
 }
 }
@@ -56,21 +70,42 @@ using namespace dev::eth::jit;
 
 extern std::jmp_buf* rt_jmpBuf;
 
-EXPORT void stack_pop(i256* _ret)
+EXPORT void stack_pop(uint64_t _count)
 {
 	auto& stack = Runtime::getStack();
-	if (stack.size() == 0)
+	if (stack.size() < _count)
 		longjmp(*rt_jmpBuf, static_cast<uint64_t>(ReturnCode::StackTooSmall));
 
-	assert(stack.size() > 0);
+	stack.erase(stack.end() - _count, stack.end());
-	*_ret = stack.back();
-	stack.pop_back();
 }
 
 EXPORT void stack_push(i256* _word)
 {
 	auto& stack = Runtime::getStack();
 	stack.push_back(*_word);
+
+	if (stack.size() > Stack::maxStackSize)
+		Stack::maxStackSize = stack.size();
+}
+
+EXPORT void stack_get(uint64_t _index, i256* _ret)
+{
+	auto& stack = Runtime::getStack();
+	// TODO: encode _index and stack size in the return code
+	if (stack.size() <= _index)
+		longjmp(*rt_jmpBuf, static_cast<uint64_t>(ReturnCode::StackTooSmall));
+
+	*_ret = *(stack.rbegin() + _index);
+}
+
+EXPORT void stack_set(uint64_t _index, i256* _word)
+{
+	auto& stack = Runtime::getStack();
+	// TODO: encode _index and stack size in the return code
+	if (stack.size() <= _index)
+		longjmp(*rt_jmpBuf, static_cast<uint64_t>(ReturnCode::StackTooSmall));
+
+	*(stack.rbegin() + _index) = *_word;
 }
 
 } // extern "C"

libevmjit/Stack.h

@@ -14,15 +14,23 @@ namespace jit
 class Stack : public CompilerHelper
 {
 public:
+
 	Stack(llvm::IRBuilder<>& builder);
 	virtual ~Stack();
 
-	void pushWord(llvm::Value* _word);
+	llvm::Value* get(size_t _index);
-	llvm::Instruction* popWord();
+	void set(size_t _index, llvm::Value* _value);
+	void pop(size_t _count);
+	void push(llvm::Value* _value);
+
+	static size_t maxStackSize;
 
 private:
+
 	llvm::Function* m_push;
 	llvm::Function* m_pop;
+	llvm::Function* m_get;
+	llvm::Function* m_set;
 
 	llvm::Value* m_arg;
 };

libevmjit/Type.cpp

@@ -13,6 +13,7 @@ namespace jit
 llvm::IntegerType* Type::i256;
 llvm::PointerType* Type::WordPtr;
 llvm::IntegerType* Type::lowPrecision;
+llvm::IntegerType* Type::Size;
 llvm::IntegerType* Type::Byte;
 llvm::PointerType* Type::BytePtr;
 llvm::Type* Type::Void;
@@ -23,6 +24,8 @@ void Type::init(llvm::LLVMContext& _context)
 	i256 = llvm::Type::getIntNTy(_context, 256);
 	WordPtr = i256->getPointerTo();
 	lowPrecision = llvm::Type::getInt64Ty(_context);
+	// TODO: Size should be architecture-dependent
+	Size = llvm::Type::getInt64Ty(_context);
 	Byte = llvm::Type::getInt8Ty(_context);
 	BytePtr = Byte->getPointerTo();
 	Void = llvm::Type::getVoidTy(_context);

libevmjit/Type.h

@@ -20,6 +20,8 @@ struct Type
 	/// @TODO: Use 64-bit for now. In 128-bit compiler-rt library functions are required
 	static llvm::IntegerType* lowPrecision;
 
+	static llvm::IntegerType* Size;
+
 	static llvm::IntegerType* Byte;
 	static llvm::PointerType* BytePtr;