Revert of SkSL performance improvements

src/sksl/SkSLIRGenerator.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
  
 #include "SkSLIRGenerator.h"
 
 #include "limits.h"
@@ skipping 50 matching lines @@
         fIR->popSymbolTable();
         ASSERT(fPrevious == fIR->fSymbolTable);
     }
 
     IRGenerator* fIR;
     std::shared_ptr<SymbolTable> fPrevious;
 };
 
 IRGenerator::IRGenerator(std::shared_ptr<SymbolTable> symbolTable, 
                          ErrorReporter& errorReporter)
-: fCurrentFunction(nullptr)
-, fSymbolTable(std::move(symbolTable))
-, fErrors(errorReporter) {}
+: fSymbolTable(std::move(symbolTable))
+, fErrors(errorReporter) {
+}
 
 void IRGenerator::pushSymbolTable() {
     fSymbolTable.reset(new SymbolTable(std::move(fSymbolTable), fErrors));
 }
 
 void IRGenerator::popSymbolTable() {
     fSymbolTable = fSymbolTable->fParent;
 }
 
 std::unique_ptr<Extension> IRGenerator::convertExtension(const ASTExtension& extension) {
@@ skipping 32 matching lines @@
 std::unique_ptr<Block> IRGenerator::convertBlock(const ASTBlock& block) {
     AutoSymbolTable table(this);
     std::vector<std::unique_ptr<Statement>> statements;
     for (size_t i = 0; i < block.fStatements.size(); i++) {
         std::unique_ptr<Statement> statement = this->convertStatement(*block.fStatements[i]);
         if (!statement) {
             return nullptr;
         }
         statements.push_back(std::move(statement));
     }
-    return std::unique_ptr<Block>(new Block(block.fPosition, std::move(statements), fSymbolTable));
+    return std::unique_ptr<Block>(new Block(block.fPosition, std::move(statements)));
 }
 
 std::unique_ptr<Statement> IRGenerator::convertVarDeclarationStatement(
                                                               const ASTVarDeclarationStatement& s) {
     auto decl = this->convertVarDeclaration(*s.fDeclaration, Variable::kLocal_Storage);
     if (!decl) {
         return nullptr;
     }
     return std::unique_ptr<Statement>(new VarDeclarationStatement(std::move(decl)));
 }
 
 Modifiers IRGenerator::convertModifiers(const ASTModifiers& modifiers) {
     return Modifiers(modifiers);
 }
 
 std::unique_ptr<VarDeclaration> IRGenerator::convertVarDeclaration(const ASTVarDeclaration& decl,
                                                                    Variable::Storage storage) {
-    std::vector<const Variable*> variables;
+    std::vector<std::shared_ptr<Variable>> variables;
     std::vector<std::vector<std::unique_ptr<Expression>>> sizes;
     std::vector<std::unique_ptr<Expression>> values;
-    const Type* baseType = this->convertType(*decl.fType);
+    std::shared_ptr<Type> baseType = this->convertType(*decl.fType);
     if (!baseType) {
         return nullptr;
     }
     for (size_t i = 0; i < decl.fNames.size(); i++) {
         Modifiers modifiers = this->convertModifiers(decl.fModifiers);
-        const Type* type = baseType;
+        std::shared_ptr<Type> type = baseType;
         ASSERT(type->kind() != Type::kArray_Kind);
         std::vector<std::unique_ptr<Expression>> currentVarSizes;
         for (size_t j = 0; j < decl.fSizes[i].size(); j++) {
             if (decl.fSizes[i][j]) {
                 ASTExpression& rawSize = *decl.fSizes[i][j];
-                auto size = this->coerce(this->convertExpression(rawSize), *kInt_Type);
+                auto size = this->coerce(this->convertExpression(rawSize), kInt_Type);
                 if (!size) {
                     return nullptr;
                 }
                 std::string name = type->fName;
                 uint64_t count;
                 if (size->fKind == Expression::kIntLiteral_Kind) {
                     count = ((IntLiteral&) *size).fValue;
                     if (count <= 0) {
                         fErrors.error(size->fPosition, "array size must be positive");
                     }
                     name += "[" + to_string(count) + "]";
                 } else {
                     count = -1;
                     name += "[]";
                 }
-                type = new Type(name, Type::kArray_Kind, *type, (int) count);
-                fSymbolTable->takeOwnership((Type*) type);
+                type = std::shared_ptr<Type>(new Type(name, Type::kArray_Kind, type, (int) count));
                 currentVarSizes.push_back(std::move(size));
             } else {
-                type = new Type(type->fName + "[]", Type::kArray_Kind, *type, -1);
-                fSymbolTable->takeOwnership((Type*) type);
+                type = std::shared_ptr<Type>(new Type(type->fName + "[]", Type::kArray_Kind, type, 
+                                                      -1));
                 currentVarSizes.push_back(nullptr);
             }
         }
         sizes.push_back(std::move(currentVarSizes));
-        auto var = std::unique_ptr<Variable>(new Variable(decl.fPosition, modifiers, decl.fNames[i], 
-                                                          *type, storage));
+        auto var = std::make_shared<Variable>(decl.fPosition, modifiers, decl.fNames[i], type, 
+                                              storage);
+        variables.push_back(var);
         std::unique_ptr<Expression> value;
         if (decl.fValues[i]) {
             value = this->convertExpression(*decl.fValues[i]);
             if (!value) {
                 return nullptr;
             }
-            value = this->coerce(std::move(value), *type);
+            value = this->coerce(std::move(value), type);
         }
-        variables.push_back(var.get());
-        fSymbolTable->add(decl.fNames[i], std::move(var));
+        fSymbolTable->add(var->fName, var);
         values.push_back(std::move(value));
     }
     return std::unique_ptr<VarDeclaration>(new VarDeclaration(decl.fPosition, std::move(variables), 
                                                               std::move(sizes), std::move(values)));
 }
 
 std::unique_ptr<Statement> IRGenerator::convertIf(const ASTIfStatement& s) {
-    std::unique_ptr<Expression> test = this->coerce(this->convertExpression(*s.fTest), *kBool_Type);
+    std::unique_ptr<Expression> test = this->coerce(this->convertExpression(*s.fTest), kBool_Type);
     if (!test) {
         return nullptr;
     }
     std::unique_ptr<Statement> ifTrue = this->convertStatement(*s.fIfTrue);
     if (!ifTrue) {
         return nullptr;
     }
     std::unique_ptr<Statement> ifFalse;
     if (s.fIfFalse) {
         ifFalse = this->convertStatement(*s.fIfFalse);
         if (!ifFalse) {
             return nullptr;
         }
     }
     return std::unique_ptr<Statement>(new IfStatement(s.fPosition, std::move(test), 
                                                       std::move(ifTrue), std::move(ifFalse)));
 }
 
 std::unique_ptr<Statement> IRGenerator::convertFor(const ASTForStatement& f) {
     AutoSymbolTable table(this);
     std::unique_ptr<Statement> initializer = this->convertStatement(*f.fInitializer);
     if (!initializer) {
         return nullptr;
     }
-    std::unique_ptr<Expression> test = this->coerce(this->convertExpression(*f.fTest), *kBool_Type);
+    std::unique_ptr<Expression> test = this->coerce(this->convertExpression(*f.fTest), kBool_Type);
     if (!test) {
         return nullptr;
     }
     std::unique_ptr<Expression> next = this->convertExpression(*f.fNext);
     if (!next) {
         return nullptr;
     }
     this->checkValid(*next);
     std::unique_ptr<Statement> statement = this->convertStatement(*f.fStatement);
     if (!statement) {
         return nullptr;
     }
     return std::unique_ptr<Statement>(new ForStatement(f.fPosition, std::move(initializer), 
                                                        std::move(test), std::move(next),
-                                                       std::move(statement), fSymbolTable));
+                                                       std::move(statement)));
 }
 
 std::unique_ptr<Statement> IRGenerator::convertWhile(const ASTWhileStatement& w) {
-    std::unique_ptr<Expression> test = this->coerce(this->convertExpression(*w.fTest), *kBool_Type);
+    std::unique_ptr<Expression> test = this->coerce(this->convertExpression(*w.fTest), kBool_Type);
     if (!test) {
         return nullptr;
     }
     std::unique_ptr<Statement> statement = this->convertStatement(*w.fStatement);
     if (!statement) {
         return nullptr;
     }
     return std::unique_ptr<Statement>(new WhileStatement(w.fPosition, std::move(test),
                                                          std::move(statement)));
 }
 
 std::unique_ptr<Statement> IRGenerator::convertDo(const ASTDoStatement& d) {
-    std::unique_ptr<Expression> test = this->coerce(this->convertExpression(*d.fTest), *kBool_Type);
+    std::unique_ptr<Expression> test = this->coerce(this->convertExpression(*d.fTest), kBool_Type);
     if (!test) {
         return nullptr;
     }
     std::unique_ptr<Statement> statement = this->convertStatement(*d.fStatement);
     if (!statement) {
         return nullptr;
     }
     return std::unique_ptr<Statement>(new DoStatement(d.fPosition, std::move(statement), 
                                                       std::move(test)));
 }
 
 std::unique_ptr<Statement> IRGenerator::convertExpressionStatement(
                                                                   const ASTExpressionStatement& s) {
     std::unique_ptr<Expression> e = this->convertExpression(*s.fExpression);
     if (!e) {
         return nullptr;
     }
     this->checkValid(*e);
     return std::unique_ptr<Statement>(new ExpressionStatement(std::move(e)));
 }
 
 std::unique_ptr<Statement> IRGenerator::convertReturn(const ASTReturnStatement& r) {
     ASSERT(fCurrentFunction);
     if (r.fExpression) {
         std::unique_ptr<Expression> result = this->convertExpression(*r.fExpression);
         if (!result) {
             return nullptr;
         }
-        if (fCurrentFunction->fReturnType == *kVoid_Type) {
+        if (fCurrentFunction->fReturnType == kVoid_Type) {
             fErrors.error(result->fPosition, "may not return a value from a void function");
         } else {
             result = this->coerce(std::move(result), fCurrentFunction->fReturnType);
             if (!result) {
                 return nullptr;
             }
         }
         return std::unique_ptr<Statement>(new ReturnStatement(std::move(result)));
     } else {
-        if (fCurrentFunction->fReturnType != *kVoid_Type) {
+        if (fCurrentFunction->fReturnType != kVoid_Type) {
             fErrors.error(r.fPosition, "expected function to return '" +
-                                       fCurrentFunction->fReturnType.description() + "'");
+                                       fCurrentFunction->fReturnType->description() + "'");
         }
         return std::unique_ptr<Statement>(new ReturnStatement(r.fPosition));
     }
 }
 
 std::unique_ptr<Statement> IRGenerator::convertBreak(const ASTBreakStatement& b) {
     return std::unique_ptr<Statement>(new BreakStatement(b.fPosition));
 }
 
 std::unique_ptr<Statement> IRGenerator::convertContinue(const ASTContinueStatement& c) {
     return std::unique_ptr<Statement>(new ContinueStatement(c.fPosition));
 }
 
 std::unique_ptr<Statement> IRGenerator::convertDiscard(const ASTDiscardStatement& d) {
     return std::unique_ptr<Statement>(new DiscardStatement(d.fPosition));
 }
 
-static const Type& expand_generics(const Type& type, int i) {
-    if (type.kind() == Type::kGeneric_Kind) {
-        return *type.coercibleTypes()[i];
+static std::shared_ptr<Type> expand_generics(std::shared_ptr<Type> type, int i) {
+    if (type->kind() == Type::kGeneric_Kind) {
+        return type->coercibleTypes()[i];
     }
     return type;
 }
 
-static void expand_generics(const FunctionDeclaration& decl, 
-                            std::shared_ptr<SymbolTable> symbolTable) {
+static void expand_generics(FunctionDeclaration& decl, 
+                            SymbolTable& symbolTable) {
     for (int i = 0; i < 4; i++) {
-        const Type& returnType = expand_generics(decl.fReturnType, i);
-        std::vector<const Variable*> parameters;
+        std::shared_ptr<Type> returnType = expand_generics(decl.fReturnType, i);
+        std::vector<std::shared_ptr<Variable>> arguments;
         for (const auto& p : decl.fParameters) {
-            Variable* var = new Variable(p->fPosition, Modifiers(p->fModifiers), p->fName,
-                                         expand_generics(p->fType, i),
-                                         Variable::kParameter_Storage);
-            symbolTable->takeOwnership(var);
-            parameters.push_back(var);
+            arguments.push_back(std::shared_ptr<Variable>(new Variable(
+                                                                    p->fPosition, 
+                                                                    Modifiers(p->fModifiers), 
+                                                                    p->fName,
+                                                                    expand_generics(p->fType, i),
+                                                                    Variable::kParameter_Storage)));
         }
-        symbolTable->add(decl.fName, std::unique_ptr<FunctionDeclaration>(new FunctionDeclaration(
-                                                                           decl.fPosition,
-                                                                           decl.fName,
-                                                                           std::move(parameters),
-                                                                           std::move(returnType))));
+        std::shared_ptr<FunctionDeclaration> expanded(new FunctionDeclaration(
+                                                                            decl.fPosition, 
+                                                                            decl.fName, 
+                                                                            std::move(arguments), 
+                                                                            std::move(returnType)));
+        symbolTable.add(expanded->fName, expanded);
     }
 }
 
 std::unique_ptr<FunctionDefinition> IRGenerator::convertFunction(const ASTFunction& f) {
+    std::shared_ptr<SymbolTable> old = fSymbolTable;
+    AutoSymbolTable table(this);
     bool isGeneric;
-    const Type* returnType = this->convertType(*f.fReturnType);
+    std::shared_ptr<Type> returnType = this->convertType(*f.fReturnType);
     if (!returnType) {
         return nullptr;
     }
     isGeneric = returnType->kind() == Type::kGeneric_Kind;
-    std::vector<const Variable*> parameters;
+    std::vector<std::shared_ptr<Variable>> parameters;
     for (const auto& param : f.fParameters) {
-        const Type* type = this->convertType(*param->fType);
+        std::shared_ptr<Type> type = this->convertType(*param->fType);
         if (!type) {
             return nullptr;
         }
         for (int j = (int) param->fSizes.size() - 1; j >= 0; j--) {
             int size = param->fSizes[j];
             std::string name = type->name() + "[" + to_string(size) + "]";
-            Type* newType = new Type(std::move(name), Type::kArray_Kind, *type, size);
-            fSymbolTable->takeOwnership(newType);
-            type = newType;
+            type = std::shared_ptr<Type>(new Type(std::move(name), Type::kArray_Kind, 
+                                                  std::move(type), size));
         }
         std::string name = param->fName;
         Modifiers modifiers = this->convertModifiers(param->fModifiers);
         Position pos = param->fPosition;
-        Variable* var = new Variable(pos, modifiers, std::move(name), *type,
-                                     Variable::kParameter_Storage);
-        fSymbolTable->takeOwnership(var);
-        parameters.push_back(var);
+        std::shared_ptr<Variable> var = std::shared_ptr<Variable>(new Variable(
+                                                                     pos, 
+                                                                     modifiers, 
+                                                                     std::move(name), 
+                                                                     type,
+                                                                     Variable::kParameter_Storage));
+        parameters.push_back(std::move(var));
         isGeneric |= type->kind() == Type::kGeneric_Kind;
     }
 
     // find existing declaration
-    const FunctionDeclaration* decl = nullptr;
-    auto entry = (*fSymbolTable)[f.fName];
+    std::shared_ptr<FunctionDeclaration> decl;
+    auto entry = (*old)[f.fName];
     if (entry) {
-        std::vector<const FunctionDeclaration*> functions;
+        std::vector<std::shared_ptr<FunctionDeclaration>> functions;
         switch (entry->fKind) {
             case Symbol::kUnresolvedFunction_Kind:
-                functions = ((UnresolvedFunction*) entry)->fFunctions;
+                functions = std::static_pointer_cast<UnresolvedFunction>(entry)->fFunctions;
                 break;
             case Symbol::kFunctionDeclaration_Kind:
-                functions.push_back((FunctionDeclaration*) entry);
+                functions.push_back(std::static_pointer_cast<FunctionDeclaration>(entry));
                 break;
             default:
                 fErrors.error(f.fPosition, "symbol '" + f.fName + "' was already defined");
                 return nullptr;
         }
         for (const auto& other : functions) {
             ASSERT(other->fName == f.fName);
             if (parameters.size() == other->fParameters.size()) {
                 bool match = true;
                 for (size_t i = 0; i < parameters.size(); i++) {
                     if (parameters[i]->fType != other->fParameters[i]->fType) {
                         match = false;
                         break;
                     }
                 }
                 if (match) {
-                    if (*returnType != other->fReturnType) {
-                        FunctionDeclaration newDecl(f.fPosition, f.fName, parameters, *returnType);
+                    if (returnType != other->fReturnType) {
+                        FunctionDeclaration newDecl = FunctionDeclaration(f.fPosition, 
+                                                                          f.fName, 
+                                                                          parameters, 
+                                                                          returnType);
                         fErrors.error(f.fPosition, "functions '" + newDecl.description() +
                                                    "' and '" + other->description() + 
                                                    "' differ only in return type");
                         return nullptr;
                     }
                     decl = other;
                     for (size_t i = 0; i < parameters.size(); i++) {
                         if (parameters[i]->fModifiers != other->fParameters[i]->fModifiers) {
                             fErrors.error(f.fPosition, "modifiers on parameter " + 
                                                        to_string(i + 1) + " differ between " +
                                                        "declaration and definition");
                             return nullptr;
                         }
+                        fSymbolTable->add(parameters[i]->fName, decl->fParameters[i]);
                     }
                     if (other->fDefined) {
                         fErrors.error(f.fPosition, "duplicate definition of " + 
                                                    other->description());
                     }
                     break;
                 }
             }
         }
     }
     if (!decl) {
         // couldn't find an existing declaration
-        if (isGeneric) {
-            ASSERT(!f.fBody);
-            expand_generics(FunctionDeclaration(f.fPosition, f.fName, parameters, *returnType), 
-                            fSymbolTable);
-        } else {
-            auto newDecl = std::unique_ptr<FunctionDeclaration>(new FunctionDeclaration(
-                                                                                     f.fPosition, 
-                                                                                     f.fName, 
-                                                                                     parameters, 
-                                                                                     *returnType));
-            decl = newDecl.get();
-            fSymbolTable->add(decl->fName, std::move(newDecl));
+        decl.reset(new FunctionDeclaration(f.fPosition, f.fName, parameters, returnType));
+        for (auto var : parameters) {
+            fSymbolTable->add(var->fName, var);
         }
     }
-    if (f.fBody) {
-        ASSERT(!fCurrentFunction);
-        fCurrentFunction = decl;
-        decl->fDefined = true;
-        std::shared_ptr<SymbolTable> old = fSymbolTable;
-        AutoSymbolTable table(this);
-        for (size_t i = 0; i < parameters.size(); i++) {
-            fSymbolTable->addWithoutOwnership(parameters[i]->fName, decl->fParameters[i]);
+    if (isGeneric) {
+        ASSERT(!f.fBody);
+        expand_generics(*decl, *old);
+    } else {
+        old->add(decl->fName, decl);
+        if (f.fBody) {
+            ASSERT(!fCurrentFunction);
+            fCurrentFunction = decl;
+            decl->fDefined = true;
+            std::unique_ptr<Block> body = this->convertBlock(*f.fBody);
+            fCurrentFunction = nullptr;
+            if (!body) {
+                return nullptr;
+            }
+            return std::unique_ptr<FunctionDefinition>(new FunctionDefinition(f.fPosition, decl, 
+                                                                              std::move(body)));
         }
-        std::unique_ptr<Block> body = this->convertBlock(*f.fBody);
-        fCurrentFunction = nullptr;
-        if (!body) {
-            return nullptr;
-        }
-        return std::unique_ptr<FunctionDefinition>(new FunctionDefinition(f.fPosition, *decl, 
-                                                                          std::move(body)));
     }
     return nullptr;
 }
 
 std::unique_ptr<InterfaceBlock> IRGenerator::convertInterfaceBlock(const ASTInterfaceBlock& intf) {
     std::shared_ptr<SymbolTable> old = fSymbolTable;
     AutoSymbolTable table(this);
     Modifiers mods = this->convertModifiers(intf.fModifiers);
     std::vector<Type::Field> fields;
     for (size_t i = 0; i < intf.fDeclarations.size(); i++) {
         std::unique_ptr<VarDeclaration> decl = this->convertVarDeclaration(
                                                                          *intf.fDeclarations[i], 
                                                                          Variable::kGlobal_Storage);
         for (size_t j = 0; j < decl->fVars.size(); j++) {
             fields.push_back(Type::Field(decl->fVars[j]->fModifiers, decl->fVars[j]->fName, 
                                          decl->fVars[j]->fType));
             if (decl->fValues[j]) {
                 fErrors.error(decl->fPosition, 
                               "initializers are not permitted on interface block fields");
             }
             if (decl->fVars[j]->fModifiers.fFlags & (Modifiers::kIn_Flag |
                                                      Modifiers::kOut_Flag |
                                                      Modifiers::kUniform_Flag |
                                                      Modifiers::kConst_Flag)) {
                 fErrors.error(decl->fPosition, 
                               "interface block fields may not have storage qualifiers");
             }
         }        
     }
-    Type* type = new Type(intf.fInterfaceName, fields);
-    fSymbolTable->takeOwnership(type);
+    std::shared_ptr<Type> type = std::shared_ptr<Type>(new Type(intf.fInterfaceName, fields));
     std::string name = intf.fValueName.length() > 0 ? intf.fValueName : intf.fInterfaceName;
-    Variable* var = new Variable(intf.fPosition, mods, name, *type, Variable::kGlobal_Storage);
-    fSymbolTable->takeOwnership(var);
+    std::shared_ptr<Variable> var = std::shared_ptr<Variable>(new Variable(intf.fPosition, mods, 
+                                                                          name, type,
+                                                                Variable::kGlobal_Storage));
     if (intf.fValueName.length()) {
-        old->addWithoutOwnership(intf.fValueName, var);
+        old->add(intf.fValueName, var);
+
     } else {
         for (size_t i = 0; i < fields.size(); i++) {
-            old->add(fields[i].fName, std::unique_ptr<Field>(new Field(intf.fPosition, *var, 
-                                                                       (int) i)));
+            std::shared_ptr<Field> field = std::shared_ptr<Field>(new Field(intf.fPosition, var, 
+                                                                            (int) i));
+            old->add(fields[i].fName, field);
         }
     }
-    return std::unique_ptr<InterfaceBlock>(new InterfaceBlock(intf.fPosition, *var, fSymbolTable));
+    return std::unique_ptr<InterfaceBlock>(new InterfaceBlock(intf.fPosition, var));
 }
 
-const Type* IRGenerator::convertType(const ASTType& type) {
-    const Symbol* result = (*fSymbolTable)[type.fName];
+std::shared_ptr<Type> IRGenerator::convertType(const ASTType& type) {
+    std::shared_ptr<Symbol> result = (*fSymbolTable)[type.fName];
     if (result && result->fKind == Symbol::kType_Kind) {
-        return (const Type*) result;
+        return std::static_pointer_cast<Type>(result);
     }
     fErrors.error(type.fPosition, "unknown type '" + type.fName + "'");
     return nullptr;
 }
 
 std::unique_ptr<Expression> IRGenerator::convertExpression(const ASTExpression& expr) {
     switch (expr.fKind) {
         case ASTExpression::kIdentifier_Kind:
             return this->convertIdentifier((ASTIdentifier&) expr);
         case ASTExpression::kBool_Kind:
@@ skipping 12 matching lines @@
         case ASTExpression::kSuffix_Kind:
             return this->convertSuffixExpression((ASTSuffixExpression&) expr);
         case ASTExpression::kTernary_Kind:
             return this->convertTernaryExpression((ASTTernaryExpression&) expr);
         default:
             ABORT("unsupported expression type: %d\n", expr.fKind);
     }
 }
 
 std::unique_ptr<Expression> IRGenerator::convertIdentifier(const ASTIdentifier& identifier) {
-    const Symbol* result = (*fSymbolTable)[identifier.fText];
+    std::shared_ptr<Symbol> result = (*fSymbolTable)[identifier.fText];
     if (!result) {
         fErrors.error(identifier.fPosition, "unknown identifier '" + identifier.fText + "'");
         return nullptr;
     }
     switch (result->fKind) {
         case Symbol::kFunctionDeclaration_Kind: {
-            std::vector<const FunctionDeclaration*> f = {
-                (const FunctionDeclaration*) result
+            std::vector<std::shared_ptr<FunctionDeclaration>> f = {
+                std::static_pointer_cast<FunctionDeclaration>(result)
             };
             return std::unique_ptr<FunctionReference>(new FunctionReference(identifier.fPosition,
-                                                                            f));
+                                                                            std::move(f)));
         }
         case Symbol::kUnresolvedFunction_Kind: {
-            const UnresolvedFunction* f = (const UnresolvedFunction*) result;
+            auto f = std::static_pointer_cast<UnresolvedFunction>(result);
             return std::unique_ptr<FunctionReference>(new FunctionReference(identifier.fPosition,
                                                                             f->fFunctions));
         }
         case Symbol::kVariable_Kind: {
-            const Variable* var = (const Variable*) result;
-            this->markReadFrom(*var);
+            std::shared_ptr<Variable> var = std::static_pointer_cast<Variable>(result);
+            this->markReadFrom(var);
             return std::unique_ptr<VariableReference>(new VariableReference(identifier.fPosition,
-                                                                            *var));
+                                                                            std::move(var)));
         }
         case Symbol::kField_Kind: {
-            const Field* field = (const Field*) result;
+            std::shared_ptr<Field> field = std::static_pointer_cast<Field>(result);
             VariableReference* base = new VariableReference(identifier.fPosition, field->fOwner);
             return std::unique_ptr<Expression>(new FieldAccess(std::unique_ptr<Expression>(base),
                                                                field->fFieldIndex));
         }
         case Symbol::kType_Kind: {
-            const Type* t = (const Type*) result;
+            auto t = std::static_pointer_cast<Type>(result);
             return std::unique_ptr<TypeReference>(new TypeReference(identifier.fPosition, 
-                                                                    *t));
+                                                                    std::move(t)));
         }
         default:
             ABORT("unsupported symbol type %d\n", result->fKind);
     }
 
 }
 
 std::unique_ptr<Expression> IRGenerator::coerce(std::unique_ptr<Expression> expr, 
-                                                const Type& type) {
+                                                std::shared_ptr<Type> type) {
     if (!expr) {
         return nullptr;
     }
-    if (expr->fType == type) {
+    if (*expr->fType == *type) {
         return expr;
     }
     this->checkValid(*expr);
-    if (expr->fType == *kInvalid_Type) {
+    if (*expr->fType == *kInvalid_Type) {
         return nullptr;
     }
-    if (!expr->fType.canCoerceTo(type)) {
-        fErrors.error(expr->fPosition, "expected '" + type.description() + "', but found '" + 
-                                        expr->fType.description() + "'");
+    if (!expr->fType->canCoerceTo(type)) {
+        fErrors.error(expr->fPosition, "expected '" + type->description() + "', but found '" + 
+                                        expr->fType->description() + "'");
         return nullptr;
     }
-    if (type.kind() == Type::kScalar_Kind) {
+    if (type->kind() == Type::kScalar_Kind) {
         std::vector<std::unique_ptr<Expression>> args;
         args.push_back(std::move(expr));
-        ASTIdentifier id(Position(), type.description());
+        ASTIdentifier id(Position(), type->description());
         std::unique_ptr<Expression> ctor = this->convertIdentifier(id);
         ASSERT(ctor);
         return this->call(Position(), std::move(ctor), std::move(args));
     }
-    ABORT("cannot coerce %s to %s", expr->fType.description().c_str(), 
-          type.description().c_str());
+    ABORT("cannot coerce %s to %s", expr->fType->description().c_str(), 
+          type->description().c_str());
 }
 
 /**
  * Determines the operand and result types of a binary expression. Returns true if the expression is
  * legal, false otherwise. If false, the values of the out parameters are undefined.
  */
-static bool determine_binary_type(Token::Kind op, const Type& left, const Type& right, 
-                                  const Type** outLeftType,
-                                  const Type** outRightType,
-                                  const Type** outResultType,
+static bool determine_binary_type(Token::Kind op, std::shared_ptr<Type> left, 
+                                  std::shared_ptr<Type> right, 
+                                  std::shared_ptr<Type>* outLeftType,
+                                  std::shared_ptr<Type>* outRightType,
+                                  std::shared_ptr<Type>* outResultType,
                                   bool tryFlipped) {
     bool isLogical;
     switch (op) {
         case Token::EQEQ: // fall through
         case Token::NEQ:  // fall through
         case Token::LT:   // fall through
         case Token::GT:   // fall through
         case Token::LTEQ: // fall through
         case Token::GTEQ:
             isLogical = true;
             break;
         case Token::LOGICALOR: // fall through
         case Token::LOGICALAND: // fall through
         case Token::LOGICALXOR: // fall through
         case Token::LOGICALOREQ: // fall through
         case Token::LOGICALANDEQ: // fall through
         case Token::LOGICALXOREQ:
             *outLeftType = kBool_Type;
             *outRightType = kBool_Type;
             *outResultType = kBool_Type;
-            return left.canCoerceTo(*kBool_Type) && right.canCoerceTo(*kBool_Type);
+            return left->canCoerceTo(kBool_Type) && right->canCoerceTo(kBool_Type);
         case Token::STAR: // fall through
         case Token::STAREQ: 
             // FIXME need to handle non-square matrices
-            if (left.kind() == Type::kMatrix_Kind && right.kind() == Type::kVector_Kind) {
-                *outLeftType = &left;
-                *outRightType = &right;
-                *outResultType = &right;
-                return left.rows() == right.columns();
+            if (left->kind() == Type::kMatrix_Kind && right->kind() == Type::kVector_Kind) {
+                *outLeftType = left;
+                *outRightType = right;
+                *outResultType = right;
+                return left->rows() == right->columns();
             }  
-            if (left.kind() == Type::kVector_Kind && right.kind() == Type::kMatrix_Kind) {
-                *outLeftType = &left;
-                *outRightType = &right;
-                *outResultType = &left;
-                return left.columns() == right.columns();
+            if (left->kind() == Type::kVector_Kind && right->kind() == Type::kMatrix_Kind) {
+                *outLeftType = left;
+                *outRightType = right;
+                *outResultType = left;
+                return left->columns() == right->columns();
             }
             // fall through
         default:
             isLogical = false;
     }
     // FIXME: need to disallow illegal operations like vec3 > vec3. Also do not currently have
     // full support for numbers other than float.
     if (left == right) {
-        *outLeftType = &left;
-        *outRightType = &left;
+        *outLeftType = left;
+        *outRightType = left;
         if (isLogical) {
             *outResultType = kBool_Type;
         } else {
-            *outResultType = &left;
+            *outResultType = left;
         }
         return true;
     }
     // FIXME: incorrect for shift operations
-    if (left.canCoerceTo(right)) {
-        *outLeftType = &right;
-        *outRightType = &right;
+    if (left->canCoerceTo(right)) {
+        *outLeftType = right;
+        *outRightType = right;
         if (isLogical) {
             *outResultType = kBool_Type;
         } else {
-            *outResultType = &right;
+            *outResultType = right;
         }
         return true;
     }
-    if ((left.kind() == Type::kVector_Kind || left.kind() == Type::kMatrix_Kind) && 
-        (right.kind() == Type::kScalar_Kind)) {
-        if (determine_binary_type(op, left.componentType(), right, outLeftType, outRightType,
+    if ((left->kind() == Type::kVector_Kind || left->kind() == Type::kMatrix_Kind) && 
+        (right->kind() == Type::kScalar_Kind)) {
+        if (determine_binary_type(op, left->componentType(), right, outLeftType, outRightType,
                                   outResultType, false)) {
-            *outLeftType = &(*outLeftType)->toCompound(left.columns(), left.rows());
+            *outLeftType = (*outLeftType)->toCompound(left->columns(), left->rows());
             if (!isLogical) {
-                *outResultType = &(*outResultType)->toCompound(left.columns(), left.rows());
+                *outResultType = (*outResultType)->toCompound(left->columns(), left->rows());
             }
             return true;
         }
         return false;
     }
     if (tryFlipped) {
         return determine_binary_type(op, right, left, outRightType, outLeftType, outResultType, 
                                      false);
     }
     return false;
 }
 
 std::unique_ptr<Expression> IRGenerator::convertBinaryExpression(
                                                             const ASTBinaryExpression& expression) {
     std::unique_ptr<Expression> left = this->convertExpression(*expression.fLeft);
     if (!left) {
         return nullptr;
     }
     std::unique_ptr<Expression> right = this->convertExpression(*expression.fRight);
     if (!right) {
         return nullptr;
     }
-    const Type* leftType;
-    const Type* rightType;
-    const Type* resultType;
+    std::shared_ptr<Type> leftType;
+    std::shared_ptr<Type> rightType;
+    std::shared_ptr<Type> resultType;
     if (!determine_binary_type(expression.fOperator, left->fType, right->fType, &leftType,
                                &rightType, &resultType, true)) {
         fErrors.error(expression.fPosition, "type mismatch: '" + 
                                             Token::OperatorName(expression.fOperator) + 
-                                            "' cannot operate on '" + left->fType.fName + 
-                                            "', '" + right->fType.fName + "'");
+                                            "' cannot operate on '" + left->fType->fName + 
+                                            "', '" + right->fType->fName + "'");
         return nullptr;
     }
     switch (expression.fOperator) {
         case Token::EQ:           // fall through
         case Token::PLUSEQ:       // fall through
         case Token::MINUSEQ:      // fall through
         case Token::STAREQ:       // fall through
         case Token::SLASHEQ:      // fall through
         case Token::PERCENTEQ:    // fall through
         case Token::SHLEQ:        // fall through
         case Token::SHREQ:        // fall through
         case Token::BITWISEOREQ:  // fall through
         case Token::BITWISEXOREQ: // fall through
         case Token::BITWISEANDEQ: // fall through
         case Token::LOGICALOREQ:  // fall through
         case Token::LOGICALXOREQ: // fall through
         case Token::LOGICALANDEQ: 
             this->markWrittenTo(*left);
         default:
             break;
     }
     return std::unique_ptr<Expression>(new BinaryExpression(expression.fPosition, 
-                                                            this->coerce(std::move(left), 
-                                                                         *leftType), 
+                                                            this->coerce(std::move(left), leftType), 
                                                             expression.fOperator, 
                                                             this->coerce(std::move(right), 
-                                                                         *rightType), 
-                                                            *resultType));
+                                                                         rightType), 
+                                                            resultType));
 }
 
 std::unique_ptr<Expression> IRGenerator::convertTernaryExpression(  
                                                            const ASTTernaryExpression& expression) {
     std::unique_ptr<Expression> test = this->coerce(this->convertExpression(*expression.fTest), 
-                                                    *kBool_Type);
+                                                    kBool_Type);
     if (!test) {
         return nullptr;
     }
     std::unique_ptr<Expression> ifTrue = this->convertExpression(*expression.fIfTrue);
     if (!ifTrue) {
         return nullptr;
     }
     std::unique_ptr<Expression> ifFalse = this->convertExpression(*expression.fIfFalse);
     if (!ifFalse) {
         return nullptr;
     }
-    const Type* trueType;
-    const Type* falseType;
-    const Type* resultType;
+    std::shared_ptr<Type> trueType;
+    std::shared_ptr<Type> falseType;
+    std::shared_ptr<Type> resultType;
     if (!determine_binary_type(Token::EQEQ, ifTrue->fType, ifFalse->fType, &trueType,
                                &falseType, &resultType, true)) {
         fErrors.error(expression.fPosition, "ternary operator result mismatch: '" + 
-                                            ifTrue->fType.fName + "', '" + 
-                                            ifFalse->fType.fName + "'");
+                                            ifTrue->fType->fName + "', '" + 
+                                            ifFalse->fType->fName + "'");
         return nullptr;
     }
     ASSERT(trueType == falseType);
-    ifTrue = this->coerce(std::move(ifTrue), *trueType);
-    ifFalse = this->coerce(std::move(ifFalse), *falseType);
+    ifTrue = this->coerce(std::move(ifTrue), trueType);
+    ifFalse = this->coerce(std::move(ifFalse), falseType);
     return std::unique_ptr<Expression>(new TernaryExpression(expression.fPosition, 
                                                              std::move(test),
                                                              std::move(ifTrue), 
                                                              std::move(ifFalse)));
 }
 
-std::unique_ptr<Expression> IRGenerator::call(Position position, 
-                                              const FunctionDeclaration& function, 
-                                              std::vector<std::unique_ptr<Expression>> arguments) {
-    if (function.fParameters.size() != arguments.size()) {
-        std::string msg = "call to '" + function.fName + "' expected " + 
-                                 to_string(function.fParameters.size()) + 
+std::unique_ptr<Expression> IRGenerator::call(
+                                         Position position, 
+                                         std::shared_ptr<FunctionDeclaration> function, 
+                                         std::vector<std::unique_ptr<Expression>> arguments) {
+    if (function->fParameters.size() != arguments.size()) {
+        std::string msg = "call to '" + function->fName + "' expected " + 
+                                 to_string(function->fParameters.size()) + 
                                  " argument";
-        if (function.fParameters.size() != 1) {
+        if (function->fParameters.size() != 1) {
             msg += "s";
         }
         msg += ", but found " + to_string(arguments.size());
         fErrors.error(position, msg);
         return nullptr;
     }
     for (size_t i = 0; i < arguments.size(); i++) {
-        arguments[i] = this->coerce(std::move(arguments[i]), function.fParameters[i]->fType);
-        if (arguments[i] && (function.fParameters[i]->fModifiers.fFlags & Modifiers::kOut_Flag)) {
+        arguments[i] = this->coerce(std::move(arguments[i]), function->fParameters[i]->fType);
+        if (arguments[i] && (function->fParameters[i]->fModifiers.fFlags & Modifiers::kOut_Flag)) {
             this->markWrittenTo(*arguments[i]);
         }
     }
-    return std::unique_ptr<FunctionCall>(new FunctionCall(position, function,
+    return std::unique_ptr<FunctionCall>(new FunctionCall(position, std::move(function),
                                                           std::move(arguments)));
 }
 
 /**
  * Determines the cost of coercing the arguments of a function to the required types. Returns true 
  * if the cost could be computed, false if the call is not valid. Cost has no particular meaning 
  * other than "lower costs are preferred".
  */
-bool IRGenerator::determineCallCost(const FunctionDeclaration& function, 
+bool IRGenerator::determineCallCost(std::shared_ptr<FunctionDeclaration> function, 
                                     const std::vector<std::unique_ptr<Expression>>& arguments,
                                     int* outCost) {
-    if (function.fParameters.size() != arguments.size()) {
+    if (function->fParameters.size() != arguments.size()) {
         return false;
     }
     int total = 0;
     for (size_t i = 0; i < arguments.size(); i++) {
         int cost;
-        if (arguments[i]->fType.determineCoercionCost(function.fParameters[i]->fType, &cost)) {
+        if (arguments[i]->fType->determineCoercionCost(function->fParameters[i]->fType, &cost)) {
             total += cost;
         } else {
             return false;
         }
     }
     *outCost = total;
     return true;
 }
 
 std::unique_ptr<Expression> IRGenerator::call(Position position, 
                                               std::unique_ptr<Expression> functionValue, 
                                               std::vector<std::unique_ptr<Expression>> arguments) {
     if (functionValue->fKind == Expression::kTypeReference_Kind) {
         return this->convertConstructor(position, 
                                         ((TypeReference&) *functionValue).fValue, 
                                         std::move(arguments));
     }
     if (functionValue->fKind != Expression::kFunctionReference_Kind) {
         fErrors.error(position, "'" + functionValue->description() + "' is not a function");
         return nullptr;
     }
     FunctionReference* ref = (FunctionReference*) functionValue.get();
     int bestCost = INT_MAX;
-    const FunctionDeclaration* best = nullptr;
+    std::shared_ptr<FunctionDeclaration> best;
     if (ref->fFunctions.size() > 1) {
         for (const auto& f : ref->fFunctions) {
             int cost;
-            if (this->determineCallCost(*f, arguments, &cost) && cost < bestCost) {
+            if (this->determineCallCost(f, arguments, &cost) && cost < bestCost) {
                 bestCost = cost;
                 best = f;
             }
         }
         if (best) {
-            return this->call(position, *best, std::move(arguments));
+            return this->call(position, std::move(best), std::move(arguments));
         }
         std::string msg = "no match for " + ref->fFunctions[0]->fName + "(";
         std::string separator = "";
         for (size_t i = 0; i < arguments.size(); i++) {
             msg += separator;
             separator = ", ";
-            msg += arguments[i]->fType.description();
+            msg += arguments[i]->fType->description();
         }
         msg += ")";
         fErrors.error(position, msg);
         return nullptr;
     }
-    return this->call(position, *ref->fFunctions[0], std::move(arguments));
+    return this->call(position, ref->fFunctions[0], std::move(arguments));
 }
 
 std::unique_ptr<Expression> IRGenerator::convertConstructor(
                                                     Position position, 
-                                                    const Type& type, 
+                                                    std::shared_ptr<Type> type, 
                                                     std::vector<std::unique_ptr<Expression>> args) {
     // FIXME: add support for structs and arrays
-    Type::Kind kind = type.kind();
-    if (!type.isNumber() && kind != Type::kVector_Kind && kind != Type::kMatrix_Kind) {
-        fErrors.error(position, "cannot construct '" + type.description() + "'");
+    Type::Kind kind = type->kind();
+    if (!type->isNumber() && kind != Type::kVector_Kind && kind != Type::kMatrix_Kind) {
+        fErrors.error(position, "cannot construct '" + type->description() + "'");
         return nullptr;
     }
-    if (type == *kFloat_Type && args.size() == 1 && 
+    if (type == kFloat_Type && args.size() == 1 && 
         args[0]->fKind == Expression::kIntLiteral_Kind) {
         int64_t value = ((IntLiteral&) *args[0]).fValue;
         return std::unique_ptr<Expression>(new FloatLiteral(position, (double) value));
     }
     if (args.size() == 1 && args[0]->fType == type) {
         // argument is already the right type, just return it
         return std::move(args[0]);
     }
-    if (type.isNumber()) {
+    if (type->isNumber()) {
         if (args.size() != 1) {
-            fErrors.error(position, "invalid arguments to '" + type.description() + 
+            fErrors.error(position, "invalid arguments to '" + type->description() + 
                                     "' constructor, (expected exactly 1 argument, but found " +
                                     to_string(args.size()) + ")");
         }
-        if (args[0]->fType == *kBool_Type) {
+        if (args[0]->fType == kBool_Type) {
             std::unique_ptr<IntLiteral> zero(new IntLiteral(position, 0));
             std::unique_ptr<IntLiteral> one(new IntLiteral(position, 1));
             return std::unique_ptr<Expression>(
                                          new TernaryExpression(position, std::move(args[0]),
                                                                this->coerce(std::move(one), type),
                                                                this->coerce(std::move(zero), 
                                                                             type)));
-        } else if (!args[0]->fType.isNumber()) {
-            fErrors.error(position, "invalid argument to '" + type.description() + 
+        } else if (!args[0]->fType->isNumber()) {
+            fErrors.error(position, "invalid argument to '" + type->description() + 
                                     "' constructor (expected a number or bool, but found '" +
-                                    args[0]->fType.description() + "')");
+                                    args[0]->fType->description() + "')");
         }
     } else {
         ASSERT(kind == Type::kVector_Kind || kind == Type::kMatrix_Kind);
         int actual = 0;
         for (size_t i = 0; i < args.size(); i++) {
-            if (args[i]->fType.kind() == Type::kVector_Kind || 
-                args[i]->fType.kind() == Type::kMatrix_Kind) {
-                int columns = args[i]->fType.columns();
-                int rows = args[i]->fType.rows();
+            if (args[i]->fType->kind() == Type::kVector_Kind || 
+                args[i]->fType->kind() == Type::kMatrix_Kind) {
+                int columns = args[i]->fType->columns();
+                int rows = args[i]->fType->rows();
                 args[i] = this->coerce(std::move(args[i]), 
-                                       type.componentType().toCompound(columns, rows));
-                actual += args[i]->fType.rows() * args[i]->fType.columns();
-            } else if (args[i]->fType.kind() == Type::kScalar_Kind) {
+                                       type->componentType()->toCompound(columns, rows));
+                actual += args[i]->fType->rows() * args[i]->fType->columns();
+            } else if (args[i]->fType->kind() == Type::kScalar_Kind) {
                 actual += 1;
-                if (type.kind() != Type::kScalar_Kind) {
-                    args[i] = this->coerce(std::move(args[i]), type.componentType());
+                if (type->kind() != Type::kScalar_Kind) {
+                    args[i] = this->coerce(std::move(args[i]), type->componentType());
                 }
             } else {
-                fErrors.error(position, "'" + args[i]->fType.description() + "' is not a valid "
-                                        "parameter to '" + type.description() + "' constructor");
+                fErrors.error(position, "'" + args[i]->fType->description() + "' is not a valid "
+                                        "parameter to '" + type->description() + "' constructor");
                 return nullptr;
             }
         }
-        int min = type.rows() * type.columns();
-        int max = type.columns() > 1 ? INT_MAX : min;
+        int min = type->rows() * type->columns();
+        int max = type->columns() > 1 ? INT_MAX : min;
         if ((actual < min || actual > max) &&
             !((kind == Type::kVector_Kind || kind == Type::kMatrix_Kind) && (actual == 1))) {
-            fErrors.error(position, "invalid arguments to '" + type.description() + 
+            fErrors.error(position, "invalid arguments to '" + type->description() + 
                                     "' constructor (expected " + to_string(min) + " scalar" + 
                                     (min == 1 ? "" : "s") + ", but found " + to_string(actual) + 
                                     ")");
             return nullptr;
         }
     }
     return std::unique_ptr<Expression>(new Constructor(position, std::move(type), std::move(args)));
 }
 
 std::unique_ptr<Expression> IRGenerator::convertPrefixExpression(
                                                             const ASTPrefixExpression& expression) {
     std::unique_ptr<Expression> base = this->convertExpression(*expression.fOperand);
     if (!base) {
         return nullptr;
     }
     switch (expression.fOperator) {
         case Token::PLUS:
-            if (!base->fType.isNumber() && base->fType.kind() != Type::kVector_Kind) {
+            if (!base->fType->isNumber() && base->fType->kind() != Type::kVector_Kind) {
                 fErrors.error(expression.fPosition, 
-                              "'+' cannot operate on '" + base->fType.description() + "'");
+                              "'+' cannot operate on '" + base->fType->description() + "'");
                 return nullptr;
             }
             return base;
         case Token::MINUS:
-            if (!base->fType.isNumber() && base->fType.kind() != Type::kVector_Kind) {
+            if (!base->fType->isNumber() && base->fType->kind() != Type::kVector_Kind) {
                 fErrors.error(expression.fPosition, 
-                              "'-' cannot operate on '" + base->fType.description() + "'");
+                              "'-' cannot operate on '" + base->fType->description() + "'");
                 return nullptr;
             }
             if (base->fKind == Expression::kIntLiteral_Kind) {
                 return std::unique_ptr<Expression>(new IntLiteral(base->fPosition,
                                                                   -((IntLiteral&) *base).fValue));
             }
             if (base->fKind == Expression::kFloatLiteral_Kind) {
                 double value = -((FloatLiteral&) *base).fValue;
                 return std::unique_ptr<Expression>(new FloatLiteral(base->fPosition, value));
             }
             return std::unique_ptr<Expression>(new PrefixExpression(Token::MINUS, std::move(base)));
         case Token::PLUSPLUS:
-            if (!base->fType.isNumber()) {
+            if (!base->fType->isNumber()) {
                 fErrors.error(expression.fPosition, 
                               "'" + Token::OperatorName(expression.fOperator) + 
-                              "' cannot operate on '" + base->fType.description() + "'");
+                              "' cannot operate on '" + base->fType->description() + "'");
                 return nullptr;
             }
             this->markWrittenTo(*base);
             break;
         case Token::MINUSMINUS: 
-            if (!base->fType.isNumber()) {
+            if (!base->fType->isNumber()) {
                 fErrors.error(expression.fPosition, 
                               "'" + Token::OperatorName(expression.fOperator) + 
-                              "' cannot operate on '" + base->fType.description() + "'");
+                              "' cannot operate on '" + base->fType->description() + "'");
                 return nullptr;
             }
             this->markWrittenTo(*base);
             break;
         case Token::NOT:
-            if (base->fType != *kBool_Type) {
+            if (base->fType != kBool_Type) {
                 fErrors.error(expression.fPosition, 
                               "'" + Token::OperatorName(expression.fOperator) + 
-                              "' cannot operate on '" + base->fType.description() + "'");
+                              "' cannot operate on '" + base->fType->description() + "'");
                 return nullptr;
             }
             break;
         default: 
             ABORT("unsupported prefix operator\n");
     }
     return std::unique_ptr<Expression>(new PrefixExpression(expression.fOperator, 
                                                             std::move(base)));
 }
 
 std::unique_ptr<Expression> IRGenerator::convertIndex(std::unique_ptr<Expression> base,
                                                       const ASTExpression& index) {
-    if (base->fType.kind() != Type::kArray_Kind && base->fType.kind() != Type::kMatrix_Kind) {
-        fErrors.error(base->fPosition, "expected array, but found '" + base->fType.description() + 
+    if (base->fType->kind() != Type::kArray_Kind && base->fType->kind() != Type::kMatrix_Kind) {
+        fErrors.error(base->fPosition, "expected array, but found '" + base->fType->description() + 
                                        "'");
         return nullptr;
     }
     std::unique_ptr<Expression> converted = this->convertExpression(index);
     if (!converted) {
         return nullptr;
     }
-    converted = this->coerce(std::move(converted), *kInt_Type);
+    converted = this->coerce(std::move(converted), kInt_Type);
     if (!converted) {
         return nullptr;
     }
     return std::unique_ptr<Expression>(new IndexExpression(std::move(base), std::move(converted)));
 }
 
 std::unique_ptr<Expression> IRGenerator::convertField(std::unique_ptr<Expression> base,
                                                       const std::string& field) {
-    auto fields = base->fType.fields();
+    auto fields = base->fType->fields();
     for (size_t i = 0; i < fields.size(); i++) {
         if (fields[i].fName == field) {
             return std::unique_ptr<Expression>(new FieldAccess(std::move(base), (int) i));
         }
     }
-    fErrors.error(base->fPosition, "type '" + base->fType.description() + "' does not have a "
+    fErrors.error(base->fPosition, "type '" + base->fType->description() + "' does not have a "
                                    "field named '" + field + "");
     return nullptr;
 }
 
 std::unique_ptr<Expression> IRGenerator::convertSwizzle(std::unique_ptr<Expression> base,
                                                         const std::string& fields) {
-    if (base->fType.kind() != Type::kVector_Kind) {
-        fErrors.error(base->fPosition, "cannot swizzle type '" + base->fType.description() + "'");
+    if (base->fType->kind() != Type::kVector_Kind) {
+        fErrors.error(base->fPosition, "cannot swizzle type '" + base->fType->description() + "'");
         return nullptr;
     }
     std::vector<int> swizzleComponents;
     for (char c : fields) {
         switch (c) {
             case 'x': // fall through
             case 'r': // fall through
             case 's': 
                 swizzleComponents.push_back(0);
                 break;
             case 'y': // fall through
             case 'g': // fall through
             case 't':
-                if (base->fType.columns() >= 2) {
+                if (base->fType->columns() >= 2) {
                     swizzleComponents.push_back(1);
                     break;
                 }
                 // fall through
             case 'z': // fall through
             case 'b': // fall through
             case 'p': 
-                if (base->fType.columns() >= 3) {
+                if (base->fType->columns() >= 3) {
                     swizzleComponents.push_back(2);
                     break;
                 }
                 // fall through
             case 'w': // fall through
             case 'a': // fall through
             case 'q':
-                if (base->fType.columns() >= 4) {
+                if (base->fType->columns() >= 4) {
                     swizzleComponents.push_back(3);
                     break;
                 }
                 // fall through
             default:
                 fErrors.error(base->fPosition, "invalid swizzle component '" + std::string(1, c) +
                                                "'");
                 return nullptr;
         }
     }
@@ skipping 22 matching lines @@
                 std::unique_ptr<Expression> converted = 
                         this->convertExpression(*(*rawArguments)[i]);
                 if (!converted) {
                     return nullptr;
                 }
                 arguments.push_back(std::move(converted));
             }
             return this->call(expression.fPosition, std::move(base), std::move(arguments));
         }
         case ASTSuffix::kField_Kind: {
-            switch (base->fType.kind()) {
+            switch (base->fType->kind()) {
                 case Type::kVector_Kind:
                     return this->convertSwizzle(std::move(base), 
                                                 ((ASTFieldSuffix&) *expression.fSuffix).fField);
                 case Type::kStruct_Kind:
                     return this->convertField(std::move(base),
                                               ((ASTFieldSuffix&) *expression.fSuffix).fField);
                 default:
                     fErrors.error(base->fPosition, "cannot swizzle value of type '" + 
-                                                   base->fType.description() + "'");
+                                                   base->fType->description() + "'");
                     return nullptr;
             }
         }
         case ASTSuffix::kPostIncrement_Kind:
-            if (!base->fType.isNumber()) {
+            if (!base->fType->isNumber()) {
                 fErrors.error(expression.fPosition, 
-                              "'++' cannot operate on '" + base->fType.description() + "'");
+                              "'++' cannot operate on '" + base->fType->description() + "'");
                 return nullptr;
             }
             this->markWrittenTo(*base);
             return std::unique_ptr<Expression>(new PostfixExpression(std::move(base), 
                                                                      Token::PLUSPLUS));
         case ASTSuffix::kPostDecrement_Kind:
-            if (!base->fType.isNumber()) {
+            if (!base->fType->isNumber()) {
                 fErrors.error(expression.fPosition, 
-                              "'--' cannot operate on '" + base->fType.description() + "'");
+                              "'--' cannot operate on '" + base->fType->description() + "'");
                 return nullptr;
             }
             this->markWrittenTo(*base);
             return std::unique_ptr<Expression>(new PostfixExpression(std::move(base), 
                                                                      Token::MINUSMINUS));
         default:
             ABORT("unsupported suffix operator");
     }
 }
 
 void IRGenerator::checkValid(const Expression& expr) {
     switch (expr.fKind) {
         case Expression::kFunctionReference_Kind:
             fErrors.error(expr.fPosition, "expected '(' to begin function call");
             break;
         case Expression::kTypeReference_Kind:
             fErrors.error(expr.fPosition, "expected '(' to begin constructor invocation");
             break;
         default:
-            ASSERT(expr.fType != *kInvalid_Type);
+            ASSERT(expr.fType != kInvalid_Type);
             break;
     }
 }
 
-void IRGenerator::markReadFrom(const Variable& var) {
-    var.fIsReadFrom = true;
+void IRGenerator::markReadFrom(std::shared_ptr<Variable> var) {
+    var->fIsReadFrom = true;
 }
 
 static bool has_duplicates(const Swizzle& swizzle) {
     int bits = 0;
     for (int idx : swizzle.fComponents) {
         ASSERT(idx >= 0 && idx <= 3);
         int bit = 1 << idx;
         if (bits & bit) {
             return true;
         }
         bits |= bit;
     }
     return false;
 }
 
 void IRGenerator::markWrittenTo(const Expression& expr) {
     switch (expr.fKind) {
         case Expression::kVariableReference_Kind: {
-            const Variable& var = ((VariableReference&) expr).fVariable;
+            const Variable& var = *((VariableReference&) expr).fVariable;
             if (var.fModifiers.fFlags & (Modifiers::kConst_Flag | Modifiers::kUniform_Flag)) {
                 fErrors.error(expr.fPosition, 
                               "cannot modify immutable variable '" + var.fName + "'");
             }
             var.fIsWrittenTo = true;
             break;
         }
         case Expression::kFieldAccess_Kind:
             this->markWrittenTo(*((FieldAccess&) expr).fBase);
             break;
         case Expression::kSwizzle_Kind:
             if (has_duplicates((Swizzle&) expr)) {
                 fErrors.error(expr.fPosition, 
                               "cannot write to the same swizzle field more than once");
             }
             this->markWrittenTo(*((Swizzle&) expr).fBase);
             break;
         case Expression::kIndex_Kind:
             this->markWrittenTo(*((IndexExpression&) expr).fBase);
             break;
         default:
             fErrors.error(expr.fPosition, "cannot assign to '" + expr.description() + "'");
             break;
     }
 }
 
 }