[clang] Don't emit type test/assume for virtual classes that should never participate in WPD

Reviewed By: pcc

Differential Revision: https://reviews.llvm.org/D127876

Author: aeubanks

Diff for: clang/docs/LTOVisibility.rst

@@ -35,13 +35,14 @@ other classes receive hidden LTO visibility. Classes with internal linkage
 (e.g. classes declared in unnamed namespaces) also receive hidden LTO
 visibility.
 
-During the LTO link, all classes with public LTO visibility will be refined
-to hidden LTO visibility when the ``--lto-whole-program-visibility`` lld linker
-option is applied (``-plugin-opt=whole-program-visibility`` for gold). This flag
-can be used to defer specifying whether classes have hidden LTO visibility until
-link time, to allow bitcode objects to be shared by different LTO links.
-Due to an implementation limitation, symbols associated with classes with hidden
-LTO visibility may still be exported from the binary when using this flag. It is
+During the LTO link, all classes with public LTO visibility but not marked with
+``[[clang::lto_visibility_public]]`` (see below) will be refined to hidden LTO
+visibility when the ``--lto-whole-program-visibility`` lld linker option is
+applied (``-plugin-opt=whole-program-visibility`` for gold).  This flag can be
+used to defer specifying whether classes have hidden LTO visibility until link
+time, to allow bitcode objects to be shared by different LTO links.  Due to an
+implementation limitation, symbols associated with classes with hidden LTO
+visibility may still be exported from the binary when using this flag. It is
 unsafe to refer to these symbols, and their visibility may be relaxed to hidden
 in a future compiler release.
 

Diff for: clang/lib/CodeGen/CGClass.cpp

@@ -2695,9 +2695,9 @@ void CodeGenFunction::EmitTypeMetadataCodeForVCall(const CXXRecordDecl *RD,
   if (SanOpts.has(SanitizerKind::CFIVCall))
     EmitVTablePtrCheckForCall(RD, VTable, CodeGenFunction::CFITCK_VCall, Loc);
   else if (CGM.getCodeGenOpts().WholeProgramVTables &&
-           // Don't insert type test assumes if we are forcing public std
+           // Don't insert type test assumes if we are forcing public
            // visibility.
-           !CGM.HasLTOVisibilityPublicStd(RD)) {
+           !CGM.AlwaysHasLTOVisibilityPublic(RD)) {
     llvm::Metadata *MD =
         CGM.CreateMetadataIdentifierForType(QualType(RD->getTypeForDecl(), 0));
     llvm::Value *TypeId =

Diff for: clang/lib/CodeGen/CGVTables.cpp

@@ -1175,7 +1175,10 @@ void CodeGenModule::EmitDeferredVTables() {
   DeferredVTables.clear();
 }
 
-bool CodeGenModule::HasLTOVisibilityPublicStd(const CXXRecordDecl *RD) {
+bool CodeGenModule::AlwaysHasLTOVisibilityPublic(const CXXRecordDecl *RD) {
+  if (RD->hasAttr<LTOVisibilityPublicAttr>() || RD->hasAttr<UuidAttr>())
+    return true;
+
   if (!getCodeGenOpts().LTOVisibilityPublicStd)
     return false;
 
@@ -1200,9 +1203,6 @@ bool CodeGenModule::HasHiddenLTOVisibility(const CXXRecordDecl *RD) {
   if (!isExternallyVisible(LV.getLinkage()))
     return true;
 
-  if (RD->hasAttr<LTOVisibilityPublicAttr>() || RD->hasAttr<UuidAttr>())
-    return false;
-
   if (getTriple().isOSBinFormatCOFF()) {
     if (RD->hasAttr<DLLExportAttr>() || RD->hasAttr<DLLImportAttr>())
       return false;
@@ -1211,7 +1211,7 @@ bool CodeGenModule::HasHiddenLTOVisibility(const CXXRecordDecl *RD) {
       return false;
   }
 
-  return !HasLTOVisibilityPublicStd(RD);
+  return !AlwaysHasLTOVisibilityPublic(RD);
 }
 
 llvm::GlobalObject::VCallVisibility CodeGenModule::GetVCallVisibilityLevel(

Diff for: clang/lib/CodeGen/CodeGenModule.h

@@ -1382,10 +1382,10 @@ class CodeGenModule : public CodeGenTypeCache {
   /// optimization.
   bool HasHiddenLTOVisibility(const CXXRecordDecl *RD);
 
-  /// Returns whether the given record has public std LTO visibility
-  /// and therefore may not participate in (single-module) CFI and whole-program
-  /// vtable optimization.
-  bool HasLTOVisibilityPublicStd(const CXXRecordDecl *RD);
+  /// Returns whether the given record has public LTO visibility (regardless of
+  /// -lto-whole-program-visibility) and therefore may not participate in
+  /// (single-module) CFI and whole-program vtable optimization.
+  bool AlwaysHasLTOVisibilityPublic(const CXXRecordDecl *RD);
 
   /// Returns the vcall visibility of the given type. This is the scope in which
   /// a virtual function call could be made which ends up being dispatched to a

Diff for: clang/lib/CodeGen/ItaniumCXXABI.cpp

@@ -668,8 +668,8 @@ CGCallee ItaniumCXXABI::EmitLoadOfMemberFunctionPointer(
                            CGM.HasHiddenLTOVisibility(RD);
   bool ShouldEmitWPDInfo =
       CGM.getCodeGenOpts().WholeProgramVTables &&
-      // Don't insert type tests if we are forcing public std visibility.
-      !CGM.HasLTOVisibilityPublicStd(RD);
+      // Don't insert type tests if we are forcing public visibility.
+      !CGM.AlwaysHasLTOVisibilityPublic(RD);
   llvm::Value *VirtualFn = nullptr;
 
   {

Diff for: clang/test/CodeGenCXX/lto-visibility-inference.cpp

@@ -79,11 +79,11 @@ void f(C1 *c1, C2 *c2, C3 *c3, C4 *c4, C5 *c5, C6 *c6, std::C7 *c7,
   // ITANIUM: type.test{{.*}}!"_ZTS2C4"
   // MS: type.test{{.*}}!"?AUC4@@"
   c4->f();
-  // ITANIUM: type.test{{.*}}!"_ZTS2C5"
-  // MS: type.test{{.*}}!"?AUC5@@"
+  // ITANIUM-NOT: type.test{{.*}}!"_ZTS2C5"
+  // MS-NOT: type.test{{.*}}!"?AUC5@@"
   c5->f();
-  // ITANIUM: type.test{{.*}}!"_ZTS2C6"
-  // MS: type.test{{.*}}!"?AUC6@@"
+  // ITANIUM-NOT: type.test{{.*}}!"_ZTS2C6"
+  // MS-NOT: type.test{{.*}}!"?AUC6@@"
   c6->f();
   // ITANIUM: type.test{{.*}}!"_ZTSSt2C7"
   // MS-STD: type.test{{.*}}!"?AUC7@std@@"