Restore "[LTO/WPD] Enable aggressive WPD under LTO option"

This restores 59733525d37cf9ad88b5021b33ecdbaf2e18911c (D71913), along
with bot fix 19c76989bb505c3117730c47df85fd3800ea2767.

The bot failure should be fixed by D73418, committed as
af954e441a5170a75687699d91d85e0692929d43.

I also added a fix for non-x86 bot failures by requiring x86 in new test
lld/test/ELF/lto/devirt_vcall_vis_public.ll.
diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index f379c10..6eff6bd 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -51,6 +51,7 @@
 #include "llvm/Transforms/Coroutines.h"
 #include "llvm/Transforms/IPO.h"
 #include "llvm/Transforms/IPO/AlwaysInliner.h"
+#include "llvm/Transforms/IPO/LowerTypeTests.h"
 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
 #include "llvm/Transforms/IPO/ThinLTOBitcodeWriter.h"
 #include "llvm/Transforms/InstCombine/InstCombine.h"
@@ -553,6 +554,16 @@
   std::unique_ptr<TargetLibraryInfoImpl> TLII(
       createTLII(TargetTriple, CodeGenOpts));
 
+  // If we reached here with a non-empty index file name, then the index file
+  // was empty and we are not performing ThinLTO backend compilation (used in
+  // testing in a distributed build environment). Drop any the type test
+  // assume sequences inserted for whole program vtables so that codegen doesn't
+  // complain.
+  if (!CodeGenOpts.ThinLTOIndexFile.empty())
+    MPM.add(createLowerTypeTestsPass(/*ExportSummary=*/nullptr,
+                                     /*ImportSummary=*/nullptr,
+                                     /*DropTypeTests=*/true));
+
   PassManagerBuilderWrapper PMBuilder(TargetTriple, CodeGenOpts, LangOpts);
 
   // At O0 and O1 we only run the always inliner which is more efficient. At
@@ -1114,6 +1125,15 @@
     bool IsLTO = CodeGenOpts.PrepareForLTO;
 
     if (CodeGenOpts.OptimizationLevel == 0) {
+      // If we reached here with a non-empty index file name, then the index
+      // file was empty and we are not performing ThinLTO backend compilation
+      // (used in testing in a distributed build environment). Drop any the type
+      // test assume sequences inserted for whole program vtables so that
+      // codegen doesn't complain.
+      if (!CodeGenOpts.ThinLTOIndexFile.empty())
+        MPM.addPass(LowerTypeTestsPass(/*ExportSummary=*/nullptr,
+                                       /*ImportSummary=*/nullptr,
+                                       /*DropTypeTests=*/true));
       if (Optional<GCOVOptions> Options = getGCOVOptions(CodeGenOpts))
         MPM.addPass(GCOVProfilerPass(*Options));
       if (Optional<InstrProfOptions> Options =
@@ -1150,6 +1170,18 @@
       // configure the pipeline.
       PassBuilder::OptimizationLevel Level = mapToLevel(CodeGenOpts);
 
+      // If we reached here with a non-empty index file name, then the index
+      // file was empty and we are not performing ThinLTO backend compilation
+      // (used in testing in a distributed build environment). Drop any the type
+      // test assume sequences inserted for whole program vtables so that
+      // codegen doesn't complain.
+      if (!CodeGenOpts.ThinLTOIndexFile.empty())
+        PB.registerPipelineStartEPCallback([](ModulePassManager &MPM) {
+          MPM.addPass(LowerTypeTestsPass(/*ExportSummary=*/nullptr,
+                                         /*ImportSummary=*/nullptr,
+                                         /*DropTypeTests=*/true));
+        });
+
       PB.registerPipelineStartEPCallback([](ModulePassManager &MPM) {
         MPM.addPass(createModuleToFunctionPassAdaptor(
             EntryExitInstrumenterPass(/*PostInlining=*/false)));
diff --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
index 3f3825b..7389207 100644
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -2641,7 +2641,9 @@
   if (SanOpts.has(SanitizerKind::CFIVCall))
     EmitVTablePtrCheckForCall(RD, VTable, CodeGenFunction::CFITCK_VCall, Loc);
   else if (CGM.getCodeGenOpts().WholeProgramVTables &&
-           CGM.HasHiddenLTOVisibility(RD)) {
+           // Don't insert type test assumes if we are forcing public std
+           // visibility.
+           !CGM.HasLTOVisibilityPublicStd(RD)) {
     llvm::Metadata *MD =
         CGM.CreateMetadataIdentifierForType(QualType(RD->getTypeForDecl(), 0));
     llvm::Value *TypeId =
diff --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
index cbc969a..403b9e2 100644
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -1011,6 +1011,26 @@
   DeferredVTables.clear();
 }
 
+bool CodeGenModule::HasLTOVisibilityPublicStd(const CXXRecordDecl *RD) {
+  if (!getCodeGenOpts().LTOVisibilityPublicStd)
+    return false;
+
+  const DeclContext *DC = RD;
+  while (1) {
+    auto *D = cast<Decl>(DC);
+    DC = DC->getParent();
+    if (isa<TranslationUnitDecl>(DC->getRedeclContext())) {
+      if (auto *ND = dyn_cast<NamespaceDecl>(D))
+        if (const IdentifierInfo *II = ND->getIdentifier())
+          if (II->isStr("std") || II->isStr("stdext"))
+            return true;
+      break;
+    }
+  }
+
+  return false;
+}
+
 bool CodeGenModule::HasHiddenLTOVisibility(const CXXRecordDecl *RD) {
   LinkageInfo LV = RD->getLinkageAndVisibility();
   if (!isExternallyVisible(LV.getLinkage()))
@@ -1027,22 +1047,7 @@
       return false;
   }
 
-  if (getCodeGenOpts().LTOVisibilityPublicStd) {
-    const DeclContext *DC = RD;
-    while (1) {
-      auto *D = cast<Decl>(DC);
-      DC = DC->getParent();
-      if (isa<TranslationUnitDecl>(DC->getRedeclContext())) {
-        if (auto *ND = dyn_cast<NamespaceDecl>(D))
-          if (const IdentifierInfo *II = ND->getIdentifier())
-            if (II->isStr("std") || II->isStr("stdext"))
-              return false;
-        break;
-      }
-    }
-  }
-
-  return true;
+  return !HasLTOVisibilityPublicStd(RD);
 }
 
 llvm::GlobalObject::VCallVisibility
diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index 115e754..a711d5c 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -1292,6 +1292,11 @@
   /// 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 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
   /// member function of this class. This scope can be wider than the visibility
diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index b5b8702..057c726 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -670,6 +670,10 @@
                             CGM.HasHiddenLTOVisibility(RD);
   bool ShouldEmitVFEInfo = CGM.getCodeGenOpts().VirtualFunctionElimination &&
                            CGM.HasHiddenLTOVisibility(RD);
+  bool ShouldEmitWPDInfo =
+      CGM.getCodeGenOpts().WholeProgramVTables &&
+      // Don't insert type tests if we are forcing public std visibility.
+      !CGM.HasLTOVisibilityPublicStd(RD);
   llvm::Value *VirtualFn = nullptr;
 
   {
@@ -677,8 +681,9 @@
     llvm::Value *TypeId = nullptr;
     llvm::Value *CheckResult = nullptr;
 
-    if (ShouldEmitCFICheck || ShouldEmitVFEInfo) {
-      // If doing CFI or VFE, we will need the metadata node to check against.
+    if (ShouldEmitCFICheck || ShouldEmitVFEInfo || ShouldEmitWPDInfo) {
+      // If doing CFI, VFE or WPD, we will need the metadata node to check
+      // against.
       llvm::Metadata *MD =
           CGM.CreateMetadataIdentifierForVirtualMemPtrType(QualType(MPT, 0));
       TypeId = llvm::MetadataAsValue::get(CGF.getLLVMContext(), MD);
@@ -702,7 +707,7 @@
     } else {
       // When not doing VFE, emit a normal load, as it allows more
       // optimisations than type.checked.load.
-      if (ShouldEmitCFICheck) {
+      if (ShouldEmitCFICheck || ShouldEmitWPDInfo) {
         CheckResult = Builder.CreateCall(
             CGM.getIntrinsic(llvm::Intrinsic::type_test),
             {Builder.CreateBitCast(VFPAddr, CGF.Int8PtrTy), TypeId});
@@ -713,7 +718,8 @@
                                             "memptr.virtualfn");
     }
     assert(VirtualFn && "Virtual fuction pointer not created!");
-    assert((!ShouldEmitCFICheck || !ShouldEmitVFEInfo || CheckResult) &&
+    assert((!ShouldEmitCFICheck || !ShouldEmitVFEInfo || !ShouldEmitWPDInfo ||
+            CheckResult) &&
            "Check result required but not created!");
 
     if (ShouldEmitCFICheck) {