diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1478650b6..7ae24b95e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -23,7 +23,7 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
 else()
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-return-type")
 endif()
-set(CMAKE_CXX_FLAGS_DEBUG "-g")
+set(CMAKE_CXX_FLAGS_DEBUG "-O1 -g")
 if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
   set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -fno-limit-debug-info")
 endif()
diff --git a/codon/parser/ast/stmt.cpp b/codon/parser/ast/stmt.cpp
index de8056a14..daac792c2 100644
--- a/codon/parser/ast/stmt.cpp
+++ b/codon/parser/ast/stmt.cpp
@@ -333,12 +333,14 @@ std::string GlobalStmt::toString(int indent) const {
 FunctionStmt::FunctionStmt(std::string name, Expr *ret, std::vector<Param> args,
                            Stmt *suite, std::vector<Expr *> decorators, bool async)
     : AcceptorExtend(), Items(std::move(args)), name(std::move(name)), ret(ret),
-      suite(SuiteStmt::wrap(suite)), decorators(std::move(decorators)), async(async) {}
+      suite(SuiteStmt::wrap(suite)), decorators(std::move(decorators)), async(async),
+      nonInferrableGenerics(nullptr) {}
 FunctionStmt::FunctionStmt(const FunctionStmt &stmt, bool clean)
     : AcceptorExtend(stmt, clean), Items(ast::clone(stmt.items, clean)),
       name(stmt.name), ret(ast::clone(stmt.ret, clean)),
       suite(ast::clone(stmt.suite, clean)),
-      decorators(ast::clone(stmt.decorators, clean)), async(stmt.async) {}
+      decorators(ast::clone(stmt.decorators, clean)), async(stmt.async),
+      nonInferrableGenerics(nullptr) {}
 std::string FunctionStmt::toString(int indent) const {
   std::string pad = indent > 0 ? ("\n" + std::string(indent + INDENT_SIZE, ' ')) : " ";
   std::vector<std::string> as;
@@ -431,8 +433,10 @@ class IdSearchVisitor : public CallbackASTVisitor<bool, bool> {
 
 /// Check if a function can be called with the given arguments.
 /// See @c reorderNamedArgs for details.
-std::unordered_set<std::string> FunctionStmt::getNonInferrableGenerics() const {
-  std::unordered_set<std::string> nonInferrableGenerics;
+const std::unordered_set<std::string> &FunctionStmt::getNonInferrableGenerics() {
+  if (nonInferrableGenerics)
+    return *nonInferrableGenerics;
+  nonInferrableGenerics = std::make_shared<std::unordered_set<std::string>>();
   for (const auto &a : items) {
     if (a.status == Param::Generic && !a.defaultValue) {
       bool inferrable = false;
@@ -444,10 +448,10 @@ std::unordered_set<std::string> FunctionStmt::getNonInferrableGenerics() const {
       if (ret && IdSearchVisitor(a.name).transform(ret))
         inferrable = true;
       if (!inferrable)
-        nonInferrableGenerics.insert(a.name);
+        nonInferrableGenerics->insert(a.name);
     }
   }
-  return nonInferrableGenerics;
+  return *nonInferrableGenerics;
 }
 
 ClassStmt::ClassStmt(std::string name, std::vector<Param> args, Stmt *suite,
diff --git a/codon/parser/ast/stmt.h b/codon/parser/ast/stmt.h
index 86692b11d..475cca769 100644
--- a/codon/parser/ast/stmt.h
+++ b/codon/parser/ast/stmt.h
@@ -3,6 +3,7 @@
 #pragma once
 
 #include <memory>
+#include <optional>
 #include <ostream>
 #include <string>
 #include <vector>
@@ -500,7 +501,11 @@ struct FunctionStmt : public AcceptorExtend<FunctionStmt, Stmt>, Items<Param> {
   void setDecorators(const std::vector<Expr *> &d) { decorators = d; }
   bool isAsync() const { return async; }
   void setAsync() { async = true; }
-  void addParam(const Param &p) { items.push_back(p); }
+  void addParam(const Param &p) {
+    items.push_back(p);
+    if (nonInferrableGenerics)
+      nonInferrableGenerics->clear();
+  }
 
   /// @return a function signature that consists of generics and arguments in a
   /// S-expression form.
@@ -509,7 +514,7 @@ struct FunctionStmt : public AcceptorExtend<FunctionStmt, Stmt>, Items<Param> {
   size_t getStarArgs() const;
   size_t getKwStarArgs() const;
   std::string getDocstr() const;
-  std::unordered_set<std::string> getNonInferrableGenerics() const;
+  const std::unordered_set<std::string> &getNonInferrableGenerics();
   bool hasFunctionAttribute(const std::string &attr) const;
 
   ACCEPT(FunctionStmt, ASTVisitor, name, items, ret, suite, decorators, async);
@@ -522,6 +527,9 @@ struct FunctionStmt : public AcceptorExtend<FunctionStmt, Stmt>, Items<Param> {
   bool async;
   std::string signature;
 
+  // Cache non-inferrable generics for speed.
+  std::shared_ptr<std::unordered_set<std::string>> nonInferrableGenerics;
+
   friend struct Cache;
 };
 
diff --git a/codon/parser/ast/types/class.cpp b/codon/parser/ast/types/class.cpp
index 5fbb297e8..4ab5f75d3 100644
--- a/codon/parser/ast/types/class.cpp
+++ b/codon/parser/ast/types/class.cpp
@@ -153,11 +153,13 @@ int ClassType::unify(Type *typ, Unification *us) {
 
 TypePtr ClassType::generalize(int atLevel) const {
   std::vector<Generic> g, hg;
+  g.reserve(generics.size());
+  hg.reserve(hiddenGenerics.size());
   for (auto &t : generics)
     g.push_back(t.generalize(atLevel));
   for (auto &t : hiddenGenerics)
     hg.push_back(t.generalize(atLevel));
-  auto c = std::make_shared<ClassType>(cache, name, g, hg);
+  auto c = std::make_shared<ClassType>(cache, name, std::move(g), std::move(hg));
   c->isTuple = isTuple;
   c->setSrcInfo(getSrcInfo());
   return c;
@@ -166,11 +168,13 @@ TypePtr ClassType::generalize(int atLevel) const {
 TypePtr ClassType::instantiate(int atLevel, int *unboundCount,
                                std::unordered_map<int, TypePtr> *cache) const {
   std::vector<Generic> g, hg;
+  g.reserve(generics.size());
+  hg.reserve(hiddenGenerics.size());
   for (auto &t : generics)
     g.push_back(t.instantiate(atLevel, unboundCount, cache));
   for (auto &t : hiddenGenerics)
     hg.push_back(t.instantiate(atLevel, unboundCount, cache));
-  auto c = std::make_shared<ClassType>(this->cache, name, g, hg);
+  auto c = std::make_shared<ClassType>(this->cache, name, std::move(g), std::move(hg));
   c->isTuple = isTuple;
   c->setSrcInfo(getSrcInfo());
   return c;
diff --git a/codon/parser/ast/types/function.cpp b/codon/parser/ast/types/function.cpp
index 41511fe7b..f383c14d4 100644
--- a/codon/parser/ast/types/function.cpp
+++ b/codon/parser/ast/types/function.cpp
@@ -15,6 +15,13 @@ FuncType::FuncType(const ClassType *baseType, FunctionStmt *ast,
     : ClassType(baseType), ast(ast), funcGenerics(std::move(funcGenerics)),
       funcParent(std::move(funcParent)) {}
 
+// Instantiation/generalization produce a private temporary base. Take its storage
+// instead of copying its generic names and shared pointers into the function type.
+FuncType::FuncType(ClassType &&baseType, FunctionStmt *ast,
+                   std::vector<Generic> funcGenerics, TypePtr funcParent)
+    : ClassType(std::move(baseType)), ast(ast), funcGenerics(std::move(funcGenerics)),
+      funcParent(std::move(funcParent)) {}
+
 int FuncType::unify(Type *typ, Unification *us) {
   if (this == typ)
     return 0;
@@ -43,18 +50,20 @@ int FuncType::unify(Type *typ, Unification *us) {
 
 TypePtr FuncType::generalize(int atLevel) const {
   std::vector<Generic> fg;
+  fg.reserve(funcGenerics.size());
   for (auto &t : funcGenerics)
     fg.push_back(t.generalize(atLevel));
   auto p = funcParent ? funcParent->generalize(atLevel) : nullptr;
 
   auto r = std::static_pointer_cast<ClassType>(this->ClassType::generalize(atLevel));
-  auto t = std::make_shared<FuncType>(r->getClass(), ast, fg, p);
+  auto t = std::make_shared<FuncType>(std::move(*r), ast, std::move(fg), std::move(p));
   return t;
 }
 
 TypePtr FuncType::instantiate(int atLevel, int *unboundCount,
                               std::unordered_map<int, TypePtr> *cache) const {
   std::vector<Generic> fg;
+  fg.reserve(funcGenerics.size());
   for (auto &t : funcGenerics) {
     fg.push_back(t.instantiate(atLevel, unboundCount, cache));
     if (cache && fg.back().type) {
@@ -65,7 +74,7 @@ TypePtr FuncType::instantiate(int atLevel, int *unboundCount,
   auto p = funcParent ? funcParent->instantiate(atLevel, unboundCount, cache) : nullptr;
   auto r = std::static_pointer_cast<ClassType>(
       this->ClassType::instantiate(atLevel, unboundCount, cache));
-  auto t = std::make_shared<FuncType>(r->getClass(), ast, fg, p);
+  auto t = std::make_shared<FuncType>(std::move(*r), ast, std::move(fg), std::move(p));
   return t;
 }
 
diff --git a/codon/parser/ast/types/function.h b/codon/parser/ast/types/function.h
index c0105e062..5bb9d7ad6 100644
--- a/codon/parser/ast/types/function.h
+++ b/codon/parser/ast/types/function.h
@@ -33,6 +33,8 @@ struct FuncType : public ClassType {
       const ClassType *baseType, FunctionStmt *ast,
       std::vector<ClassType::Generic> funcGenerics = std::vector<ClassType::Generic>(),
       TypePtr funcParent = nullptr);
+  FuncType(ClassType &&baseType, FunctionStmt *ast,
+           std::vector<ClassType::Generic> funcGenerics, TypePtr funcParent);
 
 public:
   int unify(Type *typ, Unification *undo) override;
diff --git a/codon/parser/visitors/typecheck/call.cpp b/codon/parser/visitors/typecheck/call.cpp
index 4f61b4e10..e8b5f8044 100644
--- a/codon/parser/visitors/typecheck/call.cpp
+++ b/codon/parser/visitors/typecheck/call.cpp
@@ -725,7 +725,7 @@ Expr *TypecheckVisitor::callReorderArguments(FuncType *calleeFn, CallExpr *expr,
                  typeArgs.size() == calleeFn->funcGenerics.size()),
             "bad vector sizes");
   if (!calleeFn->funcGenerics.empty()) {
-    auto niGenerics = calleeFn->ast->getNonInferrableGenerics();
+    const auto &niGenerics = calleeFn->ast->getNonInferrableGenerics();
     for (size_t si = 0; !expr->hasAttribute(Attr::ExprOrderedCall) &&
                         si < calleeFn->funcGenerics.size();
          si++) {
diff --git a/codon/parser/visitors/typecheck/typecheck.cpp b/codon/parser/visitors/typecheck/typecheck.cpp
index 5f52eb3ea..b5dc7adef 100644
--- a/codon/parser/visitors/typecheck/typecheck.cpp
+++ b/codon/parser/visitors/typecheck/typecheck.cpp
@@ -487,7 +487,7 @@ int TypecheckVisitor::canCall(types::FuncType *fn, const std::vector<CallArg> &a
   }
 
   std::vector<std::pair<types::Type *, size_t>> reordered;
-  auto niGenerics = fn->ast->getNonInferrableGenerics();
+  const auto &niGenerics = fn->ast->getNonInferrableGenerics();
   auto score = reorderNamedArgs(
       fn, args,
       [&](int s, int k, const std::vector<std::vector<int>> &slots, bool _) {
@@ -611,8 +611,9 @@ TypecheckVisitor::canWrapExpr(Type *exprType, Type *expectedType, FuncType *call
                               bool allowUnwrap, bool isEllipsis) {
   auto expectedClass = expectedType->getClass();
   auto exprClass = exprType->getClass();
-  auto doArgWrap = !callee || !callee->ast->hasFunctionAttribute(getMangledFunc(
-                                  "std.internal.attributes", "no_argument_wrap"));
+  static const auto noArgumentWrap =
+      getMangledFunc("std.internal.attributes", "no_argument_wrap");
+  auto doArgWrap = !callee || !callee->ast->hasFunctionAttribute(noArgumentWrap);
   if (!doArgWrap)
     return {true, expectedType ? expectedType->shared_from_this() : nullptr, nullptr};
 
@@ -1019,10 +1020,11 @@ TypecheckVisitor::extractNamedTuple(Expr *expr) {
 
 std::vector<Cache::Class::ClassField>
 TypecheckVisitor::getClassFields(types::ClassType *t) const {
-  auto f = getClass(t->name)->fields;
+  // Tuple has MAX_TUPLE fields; copy only the requested prefix, not the whole table.
+  const auto &f = getClass(t->name)->fields;
   if (t->is(TYPE_TUPLE))
-    f = std::vector<Cache::Class::ClassField>(f.begin(),
-                                              f.begin() + t->generics.size());
+    return std::vector<Cache::Class::ClassField>(f.begin(),
+                                                 f.begin() + t->generics.size());
   return f;
 }