diff --git a/source/opt/basic_block.h b/source/opt/basic_block.h
index 360eaefc4..62b50ceed 100644
--- a/source/opt/basic_block.h
+++ b/source/opt/basic_block.h
@@ -36,6 +36,7 @@
 #include <vector>
 
 #include "instruction.h"
+#include "iterator.h"
 
 namespace spvtools {
 namespace ir {
@@ -45,16 +46,22 @@ class Function;
 // A SPIR-V basic block.
 class BasicBlock {
  public:
-  // Creates a basic block with the given enclosing |function| and starting
-  // |label|.
-  BasicBlock(std::unique_ptr<Instruction> label)
-      : function_(nullptr), label_(std::move(label)) {}
+  using iterator = UptrVectorIterator<Instruction>;
+  using const_iterator = UptrVectorIterator<Instruction, true>;
+
+  // Creates a basic block with the given starting |label|.
+  inline explicit BasicBlock(std::unique_ptr<Instruction> label);
 
   // Sets the enclosing function for this basic block.
   void SetParent(Function* function) { function_ = function; }
   // Appends an instruction to this basic block.
   inline void AddInstruction(std::unique_ptr<Instruction> i);
 
+  iterator begin() { return iterator(&insts_, insts_.begin()); }
+  iterator end() { return iterator(&insts_, insts_.end()); }
+  const_iterator cbegin() { return const_iterator(&insts_, insts_.cbegin()); }
+  const_iterator cend() { return const_iterator(&insts_, insts_.cend()); }
+
   // Runs the given function |f| on each instruction in this basic block.
   inline void ForEachInst(const std::function<void(Instruction*)>& f);
 
@@ -71,6 +78,9 @@ class BasicBlock {
   std::vector<std::unique_ptr<Instruction>> insts_;
 };
 
+inline BasicBlock::BasicBlock(std::unique_ptr<Instruction> label)
+    : function_(nullptr), label_(std::move(label)) {}
+
 inline void BasicBlock::AddInstruction(std::unique_ptr<Instruction> i) {
   insts_.emplace_back(std::move(i));
 }
diff --git a/source/opt/function.h b/source/opt/function.h
index 70c7ff132..8615a3672 100644
--- a/source/opt/function.h
+++ b/source/opt/function.h
@@ -47,11 +47,9 @@ class Function {
   using iterator = UptrVectorIterator<BasicBlock>;
   using const_iterator = UptrVectorIterator<BasicBlock, true>;
 
-  // Creates a function instance declared by the given instruction |def_inst|.
-  Function(std::unique_ptr<Instruction> def_inst)
-      : module_(nullptr),
-        def_inst_(std::move(def_inst)),
-        end_inst_(SpvOpFunctionEnd) {}
+  // Creates a function instance declared by the given OpFunction instruction
+  // |def_inst|.
+  inline explicit Function(std::unique_ptr<Instruction> def_inst);
 
   // Sets the enclosing module for this function.
   void SetParent(Module* module) { module_ = module; }
@@ -59,6 +57,7 @@ class Function {
   inline void AddParameter(std::unique_ptr<Instruction> p);
   // Appends a basic block to this function.
   inline void AddBasicBlock(std::unique_ptr<BasicBlock> b);
+
   iterator begin() { return iterator(&blocks_, blocks_.begin()); }
   iterator end() { return iterator(&blocks_, blocks_.end()); }
   const_iterator cbegin() { return const_iterator(&blocks_, blocks_.cbegin()); }
@@ -84,6 +83,11 @@ class Function {
   Instruction end_inst_;
 };
 
+inline Function::Function(std::unique_ptr<Instruction> def_inst)
+    : module_(nullptr),
+      def_inst_(std::move(def_inst)),
+      end_inst_(SpvOpFunctionEnd) {}
+
 inline void Function::AddParameter(std::unique_ptr<Instruction> p) {
   params_.emplace_back(std::move(p));
 }
diff --git a/source/opt/module.cpp b/source/opt/module.cpp
index d83d21ef6..c08b2fd5d 100644
--- a/source/opt/module.cpp
+++ b/source/opt/module.cpp
@@ -57,6 +57,15 @@ std::vector<Instruction*> Module::GetConstants() {
   return insts;
 };
 
+std::vector<const Instruction*> Module::GetConstants() const {
+  std::vector<const Instruction*> insts;
+  for (uint32_t i = 0; i < types_values_.size(); ++i) {
+    if (IsConstantInst(types_values_[i]->opcode()))
+      insts.push_back(types_values_[i].get());
+  }
+  return insts;
+};
+
 void Module::ForEachInst(const std::function<void(Instruction*)>& f) {
   for (auto& i : capabilities_) f(i.get());
   for (auto& i : extensions_) f(i.get());
diff --git a/source/opt/module.h b/source/opt/module.h
index ac93acfc6..f34c9117b 100644
--- a/source/opt/module.h
+++ b/source/opt/module.h
@@ -94,6 +94,7 @@ class Module {
   // Returns a vector of pointers to constant-creation instructions in this
   // module.
   std::vector<Instruction*> GetConstants();
+  std::vector<const Instruction*> GetConstants() const;
 
   // Iterators for debug instructions (excluding OpLine & OpNoLine) contained in
   // this module.