Remove unnecessary jump dest map. Create jump table block on demand.

libevmjit/BasicBlock.h

@@ -67,6 +67,9 @@ public:
 	ProgramCounter begin() { return m_beginInstIdx; }
 	ProgramCounter end() { return m_endInstIdx; }
 
+	bool isJumpDest() const { return m_isJumpDest; }
+	void markAsJumpDest() { m_isJumpDest = true; }
+
 	LocalStack& localStack() { return m_stack; }
 
 	/// Optimization: propagates values between local stacks in basic blocks
@@ -109,6 +112,10 @@ private:
 	/// How many items higher is the current stack than the initial one.
 	/// May be negative.
 	int m_tosOffset = 0;
+
+	/// Is the basic block a valid jump destination.
+	/// JUMPDEST is the first instruction of the basic block.
+	bool m_isJumpDest = false;
 };
 
 }

libevmjit/Compiler.cpp

@@ -95,10 +95,27 @@ void Compiler::createBasicBlocks(bytes const& _bytecode)
 
 	m_stopBB = llvm::BasicBlock::Create(m_mainFunc->getContext(), "Stop", m_mainFunc);
 	m_badJumpBlock = std::unique_ptr<BasicBlock>(new BasicBlock("BadJumpBlock", m_mainFunc, m_builder));
-	m_jumpTableBlock = std::unique_ptr<BasicBlock>(new BasicBlock("JumpTableBlock", m_mainFunc, m_builder));
 
 	for (auto it = indirectJumpTargets.cbegin(); it != indirectJumpTargets.cend(); ++it)
-		m_jumpDests[*it] = basicBlocks.find(*it)->second.llvm();
+		basicBlocks.find(*it)->second.markAsJumpDest();
+}
+
+BasicBlock& Compiler::getJumpTableBlock()
+{
+	if (!m_jumpTableBlock)
+	{
+		m_jumpTableBlock.reset(new BasicBlock("JumpTable", m_mainFunc, m_builder));
+		InsertPointGuard g{m_builder};
+		m_builder.SetInsertPoint(m_jumpTableBlock->llvm());
+		auto dest = m_jumpTableBlock->localStack().pop();
+		auto switchInstr = m_builder.CreateSwitch(dest, m_badJumpBlock->llvm());
+		for (auto&& p : basicBlocks)
+		{
+			if (p.second.isJumpDest())
+				switchInstr->addCase(Constant::get(p.first), p.second.llvm());
+		}
+	}
+	return *m_jumpTableBlock;
 }
 
 std::unique_ptr<llvm::Module> Compiler::compile(bytes const& _bytecode, std::string const& _id)
@@ -144,21 +161,6 @@ std::unique_ptr<llvm::Module> Compiler::compile(bytes const& _bytecode, std::str
 	m_builder.SetInsertPoint(m_badJumpBlock->llvm());
 	m_builder.CreateRet(Constant::get(ReturnCode::BadJumpDestination));	
 
-	m_builder.SetInsertPoint(m_jumpTableBlock->llvm());
-	if (m_jumpDests.size() > 0)
-	{
-		auto dest = m_jumpTableBlock->localStack().pop();
-		auto switchInstr = m_builder.CreateSwitch(dest, m_badJumpBlock->llvm(), m_jumpDests.size());
-		for (auto it = m_jumpDests.cbegin(); it != m_jumpDests.cend(); ++it)
-		{
-			auto& bb = *it;
-			auto dest = Constant::get(it->first);
-			switchInstr->addCase(dest, it->second);
-		}
-	}
-	else
-		m_builder.CreateBr(m_badJumpBlock->llvm());
-
 	removeDeadBlocks();
 
 	dumpCFGifRequired("blocks-init.dot");
@@ -552,16 +554,14 @@ void Compiler::compileBasicBlock(BasicBlock& _basicBlock, bytes const& _bytecode
 				if (c.ult(_bytecode.size()))
 				{
 					auto v = c.getZExtValue();
-					auto it = m_jumpDests.find(v);
-					if (it != m_jumpDests.end())
-						targetBlock = it->second;
+					auto it = basicBlocks.find(v);
+					if (it != basicBlocks.end() && it->second.isJumpDest())
+						targetBlock = it->second.llvm();
 				}
 
 				if (!targetBlock)
-				{
 					targetBlock = m_badJumpBlock->llvm();
 			}
-			}
 
 			if (inst == Instruction::JUMP)
 			{
@@ -574,7 +574,7 @@ void Compiler::compileBasicBlock(BasicBlock& _basicBlock, bytes const& _bytecode
 				else
 				{
 					stack.push(target);
-					m_builder.CreateBr(m_jumpTableBlock->llvm());
+					m_builder.CreateBr(getJumpTableBlock().llvm());
 				}
 			}
 			else // JUMPI
@@ -594,7 +594,6 @@ void Compiler::compileBasicBlock(BasicBlock& _basicBlock, bytes const& _bytecode
 					m_builder.CreateCondBr(cond, m_jumpTableBlock->llvm(), _nextBasicBlock);
 				}
 			}
-
 			break;
 		}
 
@@ -830,13 +829,6 @@ void Compiler::removeDeadBlocks()
 		}
 	}
 	while (sthErased);
-
-	// Remove jump table block if no predecessors
-	if (llvm::pred_begin(m_jumpTableBlock->llvm()) == llvm::pred_end(m_jumpTableBlock->llvm()))
-	{
-		m_jumpTableBlock->llvm()->eraseFromParent();
-		m_jumpTableBlock.reset();
-	}
 }
 
 void Compiler::dumpCFGifRequired(std::string const& _dotfilePath)

libevmjit/Compiler.h

@@ -47,6 +47,8 @@ private:
 
 	void compileBasicBlock(BasicBlock& _basicBlock, bytes const& _bytecode, class RuntimeManager& _runtimeManager, class Arith256& _arith, class Memory& _memory, class Ext& _ext, class GasMeter& _gasMeter, llvm::BasicBlock* _nextBasicBlock);
 
+	BasicBlock& getJumpTableBlock();
+
 	void removeDeadBlocks();
 
 	/// Dumps basic block graph in graphviz format to a file, if option dumpCFG is enabled.
@@ -65,10 +67,7 @@ private:
 	llvm::IRBuilder<> m_builder;
 
 	/// Maps a program counter pc to a basic block that starts at pc (if any).
-	std::map<ProgramCounter, BasicBlock> basicBlocks = {};
-
-	/// Map of jump destinations
-	std::map<ProgramCounter, llvm::BasicBlock*> m_jumpDests = {};
+	std::map<ProgramCounter, BasicBlock> basicBlocks;
 
 	/// Stop basic block - terminates execution with STOP code (0)
 	llvm::BasicBlock* m_stopBB = nullptr;