From 33e36ce6cce1de6114bf68ce75b2d3816edfaf4b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Bylica?= <pawel.bylica@imapp.pl>
Date: Mon, 6 Oct 2014 15:58:57 +0200
Subject: [PATCH] Basic stack implementation for basic block. Values on stack
 are not preserved between basic blocks (jumps)

---
 evmcc/Compiler.cpp | 16 +++++++---------
 evmcc/Stack.cpp    | 24 ++++++++++++++++++++++++
 evmcc/Stack.h      | 22 ++++++++++++++++++++++
 3 files changed, 53 insertions(+), 9 deletions(-)

diff --git a/evmcc/Compiler.cpp b/evmcc/Compiler.cpp
index 4fead05c0..26b23bff0 100644
--- a/evmcc/Compiler.cpp
+++ b/evmcc/Compiler.cpp
@@ -188,11 +188,12 @@ std::unique_ptr<llvm::Module> Compiler::compile(const dev::bytes& bytecode)
 	createBasicBlocks(bytecode);
 
 	// Init runtime structures.
-	auto stack = Stack(builder, module.get());
+	auto globalStack = Stack(builder, module.get());
 	auto memory = Memory(builder, module.get());
 	auto ext = Ext(builder, module.get());
 
 	BasicBlock* currentBlock = entryBlock;
+	BBStack stack; // Stack for current block
 
 	for (auto pc = bytecode.cbegin(); pc != bytecode.cend(); ++pc)
 	{
@@ -211,6 +212,7 @@ std::unique_ptr<llvm::Module> Compiler::compile(const dev::bytes& bytecode)
 			mainFunc->getBasicBlockList().push_back(nextBlock);
 			builder.SetInsertPoint(nextBlock);
 			currentBlock = nextBlock;
+			stack = BBStack();	// Reset stack
 		}
 
 		assert(currentBlock != nullptr);
@@ -498,9 +500,8 @@ std::unique_ptr<llvm::Module> Compiler::compile(const dev::bytes& bytecode)
 		case Instruction::DUP15:
 		case Instruction::DUP16:
 		{
-			auto index = static_cast<uint32_t>(inst) - static_cast<uint32_t>(Instruction::DUP1);
-			auto value = stack.get(index);
-			stack.push(value);
+			auto index = static_cast<size_t>(inst) - static_cast<size_t>(Instruction::DUP1);
+			stack.dup(index);
 			break;
 		}
 
@@ -521,11 +522,8 @@ std::unique_ptr<llvm::Module> Compiler::compile(const dev::bytes& bytecode)
 		case Instruction::SWAP15:
 		case Instruction::SWAP16:
 		{
-			auto index = static_cast<uint32_t>(inst) - static_cast<uint32_t>(Instruction::SWAP1) + 1;
-			auto loValue = stack.get(index);
-			auto hiValue = stack.get(0);
-			stack.set(index, hiValue);
-			stack.set(0, loValue);
+			auto index = static_cast<size_t>(inst) - static_cast<size_t>(Instruction::SWAP1) + 1;
+			stack.swap(index);
 			break;
 		}
 
diff --git a/evmcc/Stack.cpp b/evmcc/Stack.cpp
index ef99d603b..6a4cf4d61 100644
--- a/evmcc/Stack.cpp
+++ b/evmcc/Stack.cpp
@@ -20,6 +20,30 @@
 namespace evmcc
 {
 
+void BBStack::push(llvm::Value* _value)
+{
+	m_state.push_back(_value);
+}
+
+llvm::Value* BBStack::pop()
+{
+	auto top = m_state.back();
+	m_state.pop_back();
+	return top;
+}
+
+void BBStack::dup(size_t _index)
+{
+	auto value = *(m_state.rbegin() + _index);
+	m_state.push_back(value);
+}
+
+void BBStack::swap(size_t _index)
+{
+	assert(_index != 0);
+	std::swap(*m_state.rbegin(), *(m_state.rbegin() + _index));
+}
+
 Stack::Stack(llvm::IRBuilder<>& _builder, llvm::Module* _module)
 	: m_builder(_builder)
 {
diff --git a/evmcc/Stack.h b/evmcc/Stack.h
index 53e935a8a..6336f3412 100644
--- a/evmcc/Stack.h
+++ b/evmcc/Stack.h
@@ -1,6 +1,8 @@
 
 #pragma once
 
+#include <vector>
+
 #include <llvm/IR/IRBuilder.h>
 
 namespace evmcc
@@ -26,4 +28,24 @@ private:
 	llvm::Function* m_stackSet;
 };
 
+/**
+ Stack adapter for Basic Block
+ 
+ Transforms stack to SSA: tracks values and their positions on the imaginary stack used inside a basic block.
+ */
+class BBStack
+{
+public:
+	//BBStack(llvm::IRBuilder<>& _builder, llvm::Module* _module);
+
+	void push(llvm::Value* _value);
+	llvm::Value* pop();
+	void dup(size_t _index);
+	void swap(size_t _index);
+
+private:
+	std::vector<llvm::Value*> m_state;	///< Basic black state vector - current values and their positions
+};
+
+
 }
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