[Member name lookup] Eliminate non-lazy member loading.

Lazy member loading has been in use and the default for several years
now. However, the lazy loading was disabled for any type whose primary
definition was parsed even though some of its extensions could have
been deserialized, e.g., from a Clang module. Moreover, the non-lazy
path walked all of the extensions of such a type for all member name
lookup operations. Faced with a large number of extensions to the same
type (in my example, 6,000), this walk of the list of the extensions
could dominate type-checking time.

Eliminate all effects of the `-disable-named-lazy-member-loading`
flag, and always use the "lazy" path, which effectively does no work
for parsed type definitions and extensions thereof. The example with
6,000 extensions of a single type goes from type checking in 6 seconds
down to type checking in 0.6 seconds, and name lookup completely
disappears from the profiling trace.

The deleted tests relied on the flag that is now inert. They aren't by
themselves providing much value nowadays, and it's better to have the
simpler (and more efficient) implementation of member name lookup be
the only one.

(cherry picked from commit 234534e)

Author: DougGregor

include/swift/Basic/LangOptions.h

@@ -333,9 +333,6 @@ namespace swift {
     /// Flags for developers
     ///
 
-    /// Enable named lazy member loading.
-    bool NamedLazyMemberLoading = true;
-    
     /// Whether to record request references for incremental builds.
     bool RecordRequestReferences = true;
 

lib/AST/NameLookup.cpp

@@ -1218,6 +1218,9 @@ class swift::MemberLookupTable : public ASTAllocated<swift::MemberLookupTable> {
   /// Lookup table mapping names to the set of declarations with that name.
   LookupTable Lookup;
 
+  /// List of containers that have lazily-loaded members
+  llvm::SmallVector<ExtensionDecl *, 2> ExtensionsWithLazyMembers;
+
   /// The set of names of lazily-loaded members that the lookup table has a
   /// complete accounting of with respect to all known extensions of its
   /// parent nominal type.
@@ -1246,6 +1249,14 @@ class swift::MemberLookupTable : public ASTAllocated<swift::MemberLookupTable> {
   /// Add the given members to the lookup table.
   void addMembers(DeclRange members);
 
+  void addExtensionWithLazyMembers(ExtensionDecl *ext) {
+    ExtensionsWithLazyMembers.push_back(ext);
+  }
+
+  ArrayRef<ExtensionDecl *> getExtensionsWithLazyMembers() const {
+    return ExtensionsWithLazyMembers;
+  }
+
   /// Returns \c true if the lookup table has a complete accounting of the
   /// given name.
   bool isLazilyComplete(DeclBaseName name) const {
@@ -1435,10 +1446,11 @@ void NominalTypeDecl::addedExtension(ExtensionDecl *ext) {
   auto *table = LookupTable.getPointer();
   assert(table);
 
-  if (ext->hasLazyMembers()) {
+  if (ext->wasDeserialized() || ext->hasClangNode()) {
     table->addMembers(ext->getCurrentMembersWithoutLoading());
     table->clearLazilyCompleteCache();
     table->clearLazilyCompleteForMacroExpansionCache();
+    table->addExtensionWithLazyMembers(ext);
   } else {
     table->addMembers(ext->getMembers());
   }
@@ -1534,6 +1546,9 @@ populateLookupTableEntryFromLazyIDCLoader(ASTContext &ctx,
                                           MemberLookupTable &LookupTable,
                                           DeclBaseName name,
                                           IterableDeclContext *IDC) {
+  if (!IDC->hasLazyMembers())
+    return;
+
   auto ci = ctx.getOrCreateLazyIterableContextData(IDC,
                                                    /*lazyLoader=*/nullptr);
   auto res = ci->loader->loadNamedMembers(IDC, name, ci->memberData);
@@ -1553,7 +1568,7 @@ populateLookupTableEntryFromExtensions(ASTContext &ctx,
   assert(!table.isLazilyComplete(name) &&
          "Should not be searching extensions for complete name!");
 
-  for (auto e : nominal->getExtensions()) {
+  for (auto e : table.getExtensionsWithLazyMembers()) {
     // If there's no lazy members to look at, all the members of this extension
     // are present in the lookup table.
     if (!e->hasLazyMembers()) {
@@ -1789,6 +1804,7 @@ void NominalTypeDecl::prepareLookupTable() {
     // LazyMemberLoader::loadNamedMembers().
     if (e->wasDeserialized() || e->hasClangNode()) {
       table->addMembers(e->getCurrentMembersWithoutLoading());
+      table->addExtensionWithLazyMembers(e);
       continue;
     }
 
@@ -1848,21 +1864,14 @@ DirectLookupRequest::evaluate(Evaluator &evaluator,
   const auto flags = desc.Options;
   auto *decl = desc.DC;
 
-  // We only use NamedLazyMemberLoading when a user opts-in and we have
-  // not yet loaded all the members into the IDC list in the first place.
   ASTContext &ctx = decl->getASTContext();
-  const bool useNamedLazyMemberLoading = (ctx.LangOpts.NamedLazyMemberLoading &&
-                                          decl->hasLazyMembers());
   const bool includeAttrImplements =
       flags.contains(NominalTypeDecl::LookupDirectFlags::IncludeAttrImplements);
   const bool excludeMacroExpansions =
       flags.contains(NominalTypeDecl::LookupDirectFlags::ExcludeMacroExpansions);
 
   LLVM_DEBUG(llvm::dbgs() << decl->getNameStr() << ".lookupDirect("
                           << name << ")"
-                          << ", hasLazyMembers()=" << decl->hasLazyMembers()
-                          << ", useNamedLazyMemberLoading="
-                          << useNamedLazyMemberLoading
                           << ", excludeMacroExpansions="
                           << excludeMacroExpansions
                           << "\n");
@@ -1875,15 +1884,7 @@ DirectLookupRequest::evaluate(Evaluator &evaluator,
   decl->prepareExtensions();
 
   auto &Table = *decl->getLookupTable();
-  if (!useNamedLazyMemberLoading) {
-    // Make sure we have the complete list of members (in this nominal and in
-    // all extensions).
-    (void)decl->getMembers();
-
-    for (auto E : decl->getExtensions())
-      (void)E->getMembers();
-
-  } else if (!Table.isLazilyComplete(name.getBaseName())) {
+  if (!Table.isLazilyComplete(name.getBaseName())) {
     DeclBaseName baseName(name.getBaseName());
 
     if (isa_and_nonnull<clang::NamespaceDecl>(decl->getClangDecl())) {

lib/Frontend/CompilerInvocation.cpp

@@ -649,8 +649,6 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
                                               /*default*/ false);
   Opts.UseClangFunctionTypes |= Args.hasArg(OPT_use_clang_function_types);
 
-  Opts.NamedLazyMemberLoading &= !Args.hasArg(OPT_disable_named_lazy_member_loading);
-
   if (Args.hasArg(OPT_emit_fine_grained_dependency_sourcefile_dot_files))
     Opts.EmitFineGrainedDependencySourcefileDotFiles = true;
 

test/ClangImporter/attr-swift_name-errors.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -I %S/Inputs/custom-modules -typecheck %s -disable-named-lazy-member-loading \
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -I %S/Inputs/custom-modules -typecheck %s \
 // RUN:     -verify -verify-additional-file %S/Inputs/custom-modules/ConflictingNames.h -verify-ignore-unknown
 
 // REQUIRES: objc_interop

test/ClangImporter/attr-swift_name.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t.mcp)
-// RUN: not %target-swift-frontend(mock-sdk: %clang-importer-sdk) -I %S/Inputs/custom-modules -Xcc -w -typecheck %s -module-cache-path %t.mcp -disable-named-lazy-member-loading 2>&1 | %FileCheck %s
+// RUN: not %target-swift-frontend(mock-sdk: %clang-importer-sdk) -I %S/Inputs/custom-modules -Xcc -w -typecheck %s -module-cache-path %t.mcp 2>&1 | %FileCheck %s
 
 // REQUIRES: objc_interop
 
@@ -26,12 +26,6 @@ func test(_ i: Int) {
   // CHECK: note: please report this issue to the owners of 'ObjCIRExtras'
   // CHECK-NOT: warning:
 
-  // CHECK: warning: too few parameters in swift_name attribute (expected 2; got 1)
-  // CHECK: + (instancetype)testW:(id)x out:(id *)outObject SWIFT_NAME(ww(_:));
-  // CHECK-NOT: warning:
-  // CHECK: note: please report this issue to the owners of 'ObjCIRExtras'
-  // CHECK-NOT: warning:
-
   // CHECK: warning: cycle detected while resolving 'CircularName' in swift_name attribute for 'CircularName'
   // CHECK: SWIFT_NAME(CircularName.Inner) @interface CircularName : NSObject @end
   // CHECK-NOT: {{warning|note}}: