diff --git a/src/Reactor/LLVMReactor.cpp b/src/Reactor/LLVMReactor.cpp
index 624af83..55ca049 100644
--- a/src/Reactor/LLVMReactor.cpp
+++ b/src/Reactor/LLVMReactor.cpp
@@ -1052,6 +1052,9 @@
 	void Nucleus::setInsertBlock(BasicBlock *basicBlock)
 	{
 	//	assert(::builder->GetInsertBlock()->back().isTerminator());
+
+		Variable::materializeAll();
+
 		::builder->SetInsertPoint(B(basicBlock));
 	}
 
@@ -1090,21 +1093,35 @@
 
 	void Nucleus::createRetVoid()
 	{
+		// Code generated after this point is unreachable, so any variables
+		// being read can safely return an undefined value. We have to avoid
+		// materializing variables after the terminator ret instruction.
+		Variable::killUnmaterialized();
+
 		::builder->CreateRetVoid();
 	}
 
 	void Nucleus::createRet(Value *v)
 	{
+		// Code generated after this point is unreachable, so any variables
+		// being read can safely return an undefined value. We have to avoid
+		// materializing variables after the terminator ret instruction.
+		Variable::killUnmaterialized();
+
 		::builder->CreateRet(V(v));
 	}
 
 	void Nucleus::createBr(BasicBlock *dest)
 	{
+		Variable::materializeAll();
+
 		::builder->CreateBr(B(dest));
 	}
 
 	void Nucleus::createCondBr(Value *cond, BasicBlock *ifTrue, BasicBlock *ifFalse)
 	{
+		Variable::materializeAll();
+
 		::builder->CreateCondBr(V(cond), B(ifTrue), B(ifFalse));
 	}
 
diff --git a/src/Reactor/Reactor.cpp b/src/Reactor/Reactor.cpp
index 559cb4f..b022533 100644
--- a/src/Reactor/Reactor.cpp
+++ b/src/Reactor/Reactor.cpp
@@ -14,8 +14,46 @@
 
 #include "Reactor.hpp"
 
+// Define REACTOR_MATERIALIZE_LVALUES_ON_DEFINITION to non-zero to ensure all
+// variables have a stack location obtained throuch alloca().
+#ifndef REACTOR_MATERIALIZE_LVALUES_ON_DEFINITION
+#define REACTOR_MATERIALIZE_LVALUES_ON_DEFINITION 0
+#endif
+
 namespace rr
 {
+	// Set of variables that do not have a stack location yet.
+	std::unordered_set<Variable*> Variable::unmaterializedVariables;
+
+	Variable::Variable(Type *type, int arraySize) : type(type), arraySize(arraySize)
+	{
+		#if REACTOR_MATERIALIZE_LVALUES_ON_DEFINITION
+			materialize();
+		#else
+			unmaterializedVariables.emplace(this);
+		#endif
+	}
+
+	Variable::~Variable()
+	{
+		unmaterializedVariables.erase(this);
+	}
+
+	void Variable::materializeAll()
+	{
+		for(auto *var : unmaterializedVariables)
+		{
+			var->materialize();
+		}
+
+		unmaterializedVariables.clear();
+	}
+
+	void Variable::killUnmaterialized()
+	{
+		unmaterializedVariables.clear();
+	}
+
 	static Value *createSwizzle4(Value *val, unsigned char select)
 	{
 		int swizzle[4] =
diff --git a/src/Reactor/Reactor.hpp b/src/Reactor/Reactor.hpp
index ebf2a7a..ee473a6 100644
--- a/src/Reactor/Reactor.hpp
+++ b/src/Reactor/Reactor.hpp
@@ -24,6 +24,7 @@
 
 #include <string>
 #include <tuple>
+#include <unordered_set>
 
 #undef Bool // b/127920555
 
@@ -81,16 +82,37 @@
 
 	class Variable
 	{
+		friend class Nucleus;
 		friend class PrintValue;
 
+		Variable() = delete;
 		Variable &operator=(const Variable&) = delete;
 
 	public:
-		Variable() = default;
-		Variable(const Variable&) = default;
+		void materialize() const;
+
+		Value *loadValue() const;
+		Value *storeValue(Value *value) const;
+
+		Value *getBaseAddress() const;
+		Value *getElementPointer(Value *index, bool unsignedIndex) const;
 
 	protected:
-		Value *address;
+		Variable(Type *type, int arraySize);
+		Variable(const Variable&) = default;
+
+		~Variable();
+
+	private:
+		static void materializeAll();
+		static void killUnmaterialized();
+
+		static std::unordered_set<Variable*> unmaterializedVariables;
+
+		Type *const type;
+		const int arraySize;
+		mutable Value *rvalue = nullptr;
+		mutable Value *address = nullptr;
 	};
 
 	template<class T>
@@ -105,10 +127,6 @@
 		{
 			return false;
 		}
-
-		Value *loadValue() const;
-		Value *storeValue(Value *value) const;
-		Value *getAddress(Value *index, bool unsignedIndex) const;
 	};
 
 	template<class T>
@@ -2320,33 +2338,68 @@
 namespace rr
 {
 	template<class T>
-	LValue<T>::LValue(int arraySize)
+	LValue<T>::LValue(int arraySize) : Variable(T::getType(), arraySize)
 	{
-		address = Nucleus::allocateStackVariable(T::getType(), arraySize);
 	}
 
-	template<class T>
-	Value *LValue<T>::loadValue() const
+	inline void Variable::materialize() const
 	{
-		return Nucleus::createLoad(address, T::getType(), false, 0);
+		if(!address)
+		{
+			address = Nucleus::allocateStackVariable(type, arraySize);
+
+			if(rvalue)
+			{
+				storeValue(rvalue);
+				rvalue = nullptr;
+			}
+		}
 	}
 
-	template<class T>
-	Value *LValue<T>::storeValue(Value *value) const
+	inline Value *Variable::loadValue() const
 	{
-		return Nucleus::createStore(value, address, T::getType(), false, 0);
+		if(rvalue)
+		{
+			return rvalue;
+		}
+
+		if(!address)
+		{
+			// TODO: Return undef instead.
+			materialize();
+		}
+
+		return Nucleus::createLoad(address, type, false, 0);
 	}
 
-	template<class T>
-	Value *LValue<T>::getAddress(Value *index, bool unsignedIndex) const
+	inline Value *Variable::storeValue(Value *value) const
 	{
-		return Nucleus::createGEP(address, T::getType(), index, unsignedIndex);
+		if(address)
+		{
+			return Nucleus::createStore(value, address, type, false, 0);
+		}
+
+		rvalue = value;
+
+		return value;
+	}
+
+	inline Value *Variable::getBaseAddress() const
+	{
+		materialize();
+
+		return address;
+	}
+
+	inline Value *Variable::getElementPointer(Value *index, bool unsignedIndex) const
+	{
+		return Nucleus::createGEP(getBaseAddress(), type, index, unsignedIndex);
 	}
 
 	template<class T>
 	RValue<Pointer<T>> LValue<T>::operator&()
 	{
-		return RValue<Pointer<T>>(address);
+		return RValue<Pointer<T>>(getBaseAddress());
 	}
 
 	template<class T>
@@ -2680,7 +2733,7 @@
 	template<class T, int S>
 	Reference<T> Array<T, S>::operator[](int index)
 	{
-		Value *element = LValue<T>::getAddress(Nucleus::createConstantInt(index), false);
+		Value *element = LValue<T>::getElementPointer(Nucleus::createConstantInt(index), false);
 
 		return Reference<T>(element);
 	}
@@ -2688,7 +2741,7 @@
 	template<class T, int S>
 	Reference<T> Array<T, S>::operator[](unsigned int index)
 	{
-		Value *element = LValue<T>::getAddress(Nucleus::createConstantInt(index), true);
+		Value *element = LValue<T>::getElementPointer(Nucleus::createConstantInt(index), true);
 
 		return Reference<T>(element);
 	}
@@ -2696,7 +2749,7 @@
 	template<class T, int S>
 	Reference<T> Array<T, S>::operator[](RValue<Int> index)
 	{
-		Value *element = LValue<T>::getAddress(index.value, false);
+		Value *element = LValue<T>::getElementPointer(index.value, false);
 
 		return Reference<T>(element);
 	}
@@ -2704,7 +2757,7 @@
 	template<class T, int S>
 	Reference<T> Array<T, S>::operator[](RValue<UInt> index)
 	{
-		Value *element = LValue<T>::getAddress(index.value, true);
+		Value *element = LValue<T>::getElementPointer(index.value, true);
 
 		return Reference<T>(element);
 	}
diff --git a/src/Reactor/ReactorUnitTests.cpp b/src/Reactor/ReactorUnitTests.cpp
index e44533e..a5de4f9 100644
--- a/src/Reactor/ReactorUnitTests.cpp
+++ b/src/Reactor/ReactorUnitTests.cpp
@@ -112,6 +112,65 @@
 	delete routine;
 }
 
+TEST(ReactorUnitTests, Unreachable)
+{
+	Routine *routine = nullptr;
+
+	{
+		Function<Int(Int)> function;
+		{
+			Int a = function.Arg<0>();
+			Int z = 4;
+
+			Return(a + z);
+
+			// Code beyond this point is unreachable but should not cause any
+			// compilation issues.
+
+			z += a;
+		}
+
+		routine = function("one");
+
+		if(routine)
+		{
+			int (*callable)(int) = (int(*)(int))routine->getEntry();
+			int result = callable(16);
+			EXPECT_EQ(result, 20);
+		}
+	}
+
+	delete routine;
+}
+
+TEST(ReactorUnitTests, VariableAddress)
+{
+	Routine *routine = nullptr;
+
+	{
+		Function<Int(Int)> function;
+		{
+			Int a = function.Arg<0>();
+			Int z = 0;
+			Pointer<Int> p = &z;
+			*p = 4;
+
+			Return(a + z);
+		}
+
+		routine = function("one");
+
+		if(routine)
+		{
+			int (*callable)(int) = (int(*)(int))routine->getEntry();
+			int result = callable(16);
+			EXPECT_EQ(result, 20);
+		}
+	}
+
+	delete routine;
+}
+
 TEST(ReactorUnitTests, SubVectorLoadStore)
 {
 	Routine *routine = nullptr;
diff --git a/src/Reactor/SubzeroReactor.cpp b/src/Reactor/SubzeroReactor.cpp
index fce1717..dee4af0 100644
--- a/src/Reactor/SubzeroReactor.cpp
+++ b/src/Reactor/SubzeroReactor.cpp
@@ -649,6 +649,9 @@
 	void Nucleus::setInsertBlock(BasicBlock *basicBlock)
 	{
 	//	assert(::basicBlock->getInsts().back().getTerminatorEdges().size() >= 0 && "Previous basic block must have a terminator");
+
+		Variable::materializeAll();
+
 		::basicBlock = basicBlock;
 	}
 
@@ -676,24 +679,38 @@
 
 	void Nucleus::createRetVoid()
 	{
+		// Code generated after this point is unreachable, so any variables
+		// being read can safely return an undefined value. We have to avoid
+		// materializing variables after the terminator ret instruction.
+		Variable::killUnmaterialized();
+
 		Ice::InstRet *ret = Ice::InstRet::create(::function);
 		::basicBlock->appendInst(ret);
 	}
 
 	void Nucleus::createRet(Value *v)
 	{
+		// Code generated after this point is unreachable, so any variables
+		// being read can safely return an undefined value. We have to avoid
+		// materializing variables after the terminator ret instruction.
+		Variable::killUnmaterialized();
+
 		Ice::InstRet *ret = Ice::InstRet::create(::function, v);
 		::basicBlock->appendInst(ret);
 	}
 
 	void Nucleus::createBr(BasicBlock *dest)
 	{
+		Variable::materializeAll();
+
 		auto br = Ice::InstBr::create(::function, dest);
 		::basicBlock->appendInst(br);
 	}
 
 	void Nucleus::createCondBr(Value *cond, BasicBlock *ifTrue, BasicBlock *ifFalse)
 	{
+		Variable::materializeAll();
+
 		auto br = Ice::InstBr::create(::function, cond, ifTrue, ifFalse);
 		::basicBlock->appendInst(br);
 	}