[Type checker] Remove some pointless cached state from the type checker.

We can retrieve these standard library declarations from the ASTContext
easily enough, and the interface type is already cached, so do that.

Author: DougGregor

lib/Sema/TypeCheckType.cpp

@@ -420,46 +420,47 @@ Type TypeChecker::getUnsafeMutablePointerType(SourceLoc loc, Type pointeeType) {
   return getPointerType(*this, loc, pointeeType, PTK_UnsafeMutablePointer);
 }
 
-static Type getStdlibType(TypeChecker &TC, Type &cached, DeclContext *dc,
-                          StringRef name) {
-  if (cached.isNull()) {
-    ModuleDecl *stdlib = TC.Context.getStdlibModule();
-    LookupTypeResult lookup = TC.lookupMemberType(dc, ModuleType::get(stdlib),
-                                                  TC.Context.getIdentifier(
-                                                    name));
-    if (lookup)
-      cached = lookup.back().MemberType;
-  }
-  return cached;
-}
-
 Type TypeChecker::getStringType(DeclContext *dc) {
-  return ::getStdlibType(*this, StringType, dc, "String");
+  if (auto typeDecl = Context.getStringDecl())
+    return typeDecl->getDeclaredInterfaceType();
+
+  return Type();
 }
+
 Type TypeChecker::getSubstringType(DeclContext *dc) {
-  return ::getStdlibType(*this, SubstringType, dc, "Substring");
+  if (auto typeDecl = Context.getSubstringDecl())
+    return typeDecl->getDeclaredInterfaceType();
+
+  return Type();
 }
+
 Type TypeChecker::getIntType(DeclContext *dc) {
-  return ::getStdlibType(*this, IntType, dc, "Int");
+  if (auto typeDecl = Context.getIntDecl())
+    return typeDecl->getDeclaredInterfaceType();
+
+  return Type();
 }
+
 Type TypeChecker::getInt8Type(DeclContext *dc) {
-  return ::getStdlibType(*this, Int8Type, dc, "Int8");
+  if (auto typeDecl = Context.getInt8Decl())
+    return typeDecl->getDeclaredInterfaceType();
+
+  return Type();
 }
+
 Type TypeChecker::getUInt8Type(DeclContext *dc) {
-  return ::getStdlibType(*this, UInt8Type, dc, "UInt8");
+  if (auto typeDecl = Context.getUInt8Decl())
+    return typeDecl->getDeclaredInterfaceType();
+
+  return Type();
 }
 
 /// Find the standard type of exceptions.
 ///
 /// We call this the "exception type" to try to avoid confusion with
 /// the AST's ErrorType node.
 Type TypeChecker::getExceptionType(DeclContext *dc, SourceLoc loc) {
-  if (NominalTypeDecl *decl = Context.getErrorDecl())
-    return decl->getDeclaredType();
-
-  // Not really sugar, but the actual diagnostic text is fine.
-  diagnose(loc, diag::sugar_type_not_found, 4);
-  return Type();
+  return Context.getErrorDecl()->getDeclaredType();
 }
 
 Type

lib/Sema/TypeChecker.h

@@ -663,19 +663,10 @@ class TypeChecker final : public LazyResolver {
 
 private:
   Type MaxIntegerType;
-  Type StringType;
-  Type SubstringType;
-  Type IntType;
-  Type Int8Type;
-  Type UInt8Type;
   Type NSObjectType;
   Type NSNumberType;
   Type NSValueType;
   Type ObjCSelectorType;
-  Type ExceptionType;
-
-  /// The \c Swift.UnsafeMutablePointer<T> declaration.
-  Optional<NominalTypeDecl *> ArrayDecl;
 
   /// The set of expressions currently being analyzed for failures.
   llvm::DenseMap<Expr*, Expr*> DiagnosedExprs;