diff --git a/src/Reactor/LLVMReactor.cpp b/src/Reactor/LLVMReactor.cpp
index bc214f3..3a56b4c 100644
--- a/src/Reactor/LLVMReactor.cpp
+++ b/src/Reactor/LLVMReactor.cpp
@@ -1781,6 +1781,12 @@
 	return V(ptr);
 }
 
+void Nucleus::setOptimizerCallback(OptimizerCallback *callback)
+{
+	// The LLVM backend does not produce optimizer reports.
+	(void)callback;
+}
+
 Type *Void::type()
 {
 	return T(llvm::Type::getVoidTy(*jit->context));
diff --git a/src/Reactor/Nucleus.hpp b/src/Reactor/Nucleus.hpp
index 4d2b003..d430845 100644
--- a/src/Reactor/Nucleus.hpp
+++ b/src/Reactor/Nucleus.hpp
@@ -333,6 +333,20 @@
 	static Type *getContainedType(Type *vectorType);
 	static Type *getPointerType(Type *elementType);
 	static Type *getPrintfStorageType(Type *valueType);
+
+	// Diagnostic utilities
+	struct OptimizerReport
+	{
+		int allocas = 0;
+		int loads = 0;
+		int stores = 0;
+	};
+
+	using OptimizerCallback = void(const OptimizerReport *report);
+
+	// Sets the callback to be used by the next optimizer invocation (during acquireRoutine),
+	// for reporting stats about the resulting IR code. For testing only.
+	static void setOptimizerCallback(OptimizerCallback *callback);
 };
 
 }  // namespace rr
diff --git a/src/Reactor/Optimizer.cpp b/src/Reactor/Optimizer.cpp
index d5f95e8..8ec7af1 100644
--- a/src/Reactor/Optimizer.cpp
+++ b/src/Reactor/Optimizer.cpp
@@ -24,6 +24,11 @@
 class Optimizer
 {
 public:
+	Optimizer(rr::Nucleus::OptimizerReport *report)
+	    : report(report)
+	{
+	}
+
 	void run(Ice::Cfg *function);
 
 private:
@@ -46,6 +51,8 @@
 	static std::size_t storeSize(const Ice::Inst *instruction);
 	static bool loadTypeMatchesStore(const Ice::Inst *load, const Ice::Inst *store);
 
+	void collectDiagnostics();
+
 	Ice::Cfg *function;
 	Ice::GlobalContext *context;
 
@@ -88,6 +95,8 @@
 	bool hasLoadStoreInsts(Ice::CfgNode *node) const;
 
 	std::vector<Ice::Operand *> operandsWithUses;
+
+	rr::Nucleus::OptimizerReport *report = nullptr;
 };
 
 void Optimizer::run(Ice::Cfg *function)
@@ -115,6 +124,8 @@
 		setUses(operand, nullptr);
 	}
 	operandsWithUses.clear();
+
+	collectDiagnostics();
 }
 
 // Eliminates allocas which store the address of other allocas.
@@ -719,6 +730,38 @@
 	return true;
 }
 
+void Optimizer::collectDiagnostics()
+{
+	if(report)
+	{
+		*report = {};
+
+		for(auto *basicBlock : function->getNodes())
+		{
+			for(auto &inst : basicBlock->getInsts())
+			{
+				if(inst.isDeleted())
+				{
+					continue;
+				}
+
+				if(llvm::isa<Ice::InstAlloca>(inst))
+				{
+					report->allocas++;
+				}
+				else if(isLoad(inst))
+				{
+					report->loads++;
+				}
+				else if(isStore(inst))
+				{
+					report->stores++;
+				}
+			}
+		}
+	}
+}
+
 Optimizer::Uses *Optimizer::getUses(Ice::Operand *operand)
 {
 	Optimizer::Uses *uses = (Optimizer::Uses *)operand->Ice::Operand::getExternalData();
@@ -846,9 +889,9 @@
 
 namespace rr {
 
-void optimize(Ice::Cfg *function)
+void optimize(Ice::Cfg *function, Nucleus::OptimizerReport *report)
 {
-	Optimizer optimizer;
+	Optimizer optimizer(report);
 
 	optimizer.run(function);
 }
diff --git a/src/Reactor/Optimizer.hpp b/src/Reactor/Optimizer.hpp
index b51c74a..7d82a93 100644
--- a/src/Reactor/Optimizer.hpp
+++ b/src/Reactor/Optimizer.hpp
@@ -15,11 +15,13 @@
 #ifndef rr_Optimizer_hpp
 #define rr_Optimizer_hpp
 
+#include "Nucleus.hpp"
+
 #include "src/IceCfg.h"
 
 namespace rr {
 
-void optimize(Ice::Cfg *function);
+void optimize(Ice::Cfg *function, Nucleus::OptimizerReport *report = nullptr);
 
 }  // namespace rr
 
diff --git a/src/Reactor/SubzeroReactor.cpp b/src/Reactor/SubzeroReactor.cpp
index 53377ca..ada1072 100644
--- a/src/Reactor/SubzeroReactor.cpp
+++ b/src/Reactor/SubzeroReactor.cpp
@@ -241,6 +241,9 @@
 
 	return *scheduler;
 }
+
+rr::Nucleus::OptimizerCallback *optimizerCallback = nullptr;
+
 }  // Anonymous namespace
 
 namespace {
@@ -1008,7 +1011,17 @@
 
 		currFunc->setFunctionName(Ice::GlobalString::createWithString(::context, names[i]));
 
-		rr::optimize(currFunc);
+		if(::optimizerCallback)
+		{
+			Nucleus::OptimizerReport report;
+			rr::optimize(currFunc, &report);
+			::optimizerCallback(&report);
+			::optimizerCallback = nullptr;
+		}
+		else
+		{
+			rr::optimize(currFunc);
+		}
 
 		currFunc->computeInOutEdges();
 		ASSERT_MSG(!currFunc->hasError(), "%s", currFunc->getError().c_str());
@@ -2186,6 +2199,11 @@
 	return V(IceConstantData(v, strlen(v) + 1));
 }
 
+void Nucleus::setOptimizerCallback(OptimizerCallback *callback)
+{
+	::optimizerCallback = callback;
+}
+
 Type *Void::type()
 {
 	return T(Ice::IceType_void);
diff --git a/tests/ReactorUnitTests/ReactorUnitTests.cpp b/tests/ReactorUnitTests/ReactorUnitTests.cpp
index 6b85a48..51a7531 100644
--- a/tests/ReactorUnitTests/ReactorUnitTests.cpp
+++ b/tests/ReactorUnitTests/ReactorUnitTests.cpp
@@ -395,7 +395,6 @@
 
 // This test excercises the Optimizer::eliminateLoadsFollowingSingleStore() optimization pass.
 // The three load operations for `y` should get eliminated.
-// TODO(b/180665600): Check that the optimization took place.
 TEST(ReactorUnitTests, EliminateLoadsFollowingSingleStore)
 {
 	FunctionT<int(int)> function;
@@ -415,6 +414,12 @@
 		Return(z);
 	}
 
+	Nucleus::setOptimizerCallback([](const Nucleus::OptimizerReport *report) {
+		EXPECT_EQ(report->allocas, 2);
+		EXPECT_EQ(report->loads, 2);
+		EXPECT_EQ(report->stores, 2);
+	});
+
 	auto routine = function(testName().c_str());
 
 	int result = routine(11);
@@ -423,7 +428,6 @@
 
 // This test excercises the Optimizer::propagateAlloca() optimization pass.
 // The pointer variable should not get stored to / loaded from memory.
-// TODO(b/180665600): Check that the optimization took place.
 TEST(ReactorUnitTests, PropagateAlloca)
 {
 	FunctionT<int(int)> function;
@@ -443,6 +447,12 @@
 		Return(Int(*p));  // TODO(b/179694472): Support Return(*p)
 	}
 
+	Nucleus::setOptimizerCallback([](const Nucleus::OptimizerReport *report) {
+		EXPECT_EQ(report->allocas, 1);
+		EXPECT_EQ(report->loads, 1);
+		EXPECT_EQ(report->stores, 1);
+	});
+
 	auto routine = function(testName().c_str());
 
 	int result = routine(true);