[compiler-rt] [llvm] [clang-tools-extra] [clang] [IRPGO][ValueProfile] Instrument virtual table address that could be used to do virtual table address comparision for indirect-call-promotion. (PR #66825)

[Snehasish Kumar via cfe-commits]

================
@@ -1070,8 +1084,138 @@ void InstrProfiling::maybeSetComdat(GlobalVariable *GV, Function *Fn,
     GV->setLinkage(GlobalValue::InternalLinkage);
 }
 
-GlobalVariable *InstrProfiling::setupProfileSection(InstrProfInstBase *Inc,
-                                                    InstrProfSectKind IPSK) {
+static inline bool shouldRecordVTableAddr(GlobalVariable *GV) {
+  if (!profDataReferencedByCode(*GV->getParent()))
+    return false;
+
+  if (!GV->hasLinkOnceLinkage() && !GV->hasLocalLinkage() &&
+      !GV->hasAvailableExternallyLinkage())
+    return true;
+
+  // This avoids the profile data from referencing internal symbols in
+  // COMDAT.
+  if (GV->hasLocalLinkage() && GV->hasComdat())
+    return false;
+
+  return true;
+}
+
+// FIXME: Does symbollic relocation from 'getFuncAddrForProfData' matter here?
+static inline Constant *getVTableAddrForProfData(GlobalVariable *GV) {
+  auto *Int8PtrTy = Type::getInt8PtrTy(GV->getContext());
+
+  // Store a nullptr in __profvt_ if a real address shouldn't be used.
+  if (!shouldRecordVTableAddr(GV))
+    return ConstantPointerNull::get(Int8PtrTy);
+
+  return ConstantExpr::getBitCast(GV, Int8PtrTy);
+}
+
+/// Get the name of a profiling variable for a particular variable.
+static std::string getVarName(GlobalVariable *GV, StringRef Prefix) {
+  StringRef Name = getPGOName(*GV);
+  return (Prefix + Name).str();
+}
+
+void InstrProfiling::getOrCreateVTableProfData(GlobalVariable *GV) {
+  assert(!DebugInfoCorrelate &&
+         "Value profiling is not supported with lightweight instrumentation");
+  if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
+    return;
+
+  if (GV->getName().starts_with("llvm.") ||
+      GV->getName().starts_with("__llvm") ||
+      GV->getName().starts_with("__prof"))
+    return;
+
+  // VTableProfData already created
+  auto It = VTableDataMap.find(GV);
+  if (It != VTableDataMap.end() && It->second)
+    return;
+
+  GlobalValue::LinkageTypes Linkage = GV->getLinkage();
+  GlobalValue::VisibilityTypes Visibility = GV->getVisibility();
+
+  // This is to keep consistent with per-function profile data
+  // for correctness.
+  if (TT.isOSBinFormatXCOFF()) {
+    Linkage = GlobalValue::InternalLinkage;
+    Visibility = GlobalValue::DefaultVisibility;
+  }
+
+  LLVMContext &Ctx = M->getContext();
+  Type *DataTypes[] = {
+#define INSTR_PROF_VTABLE_DATA(Type, LLVMType, Name, Init) LLVMType,
+#include "llvm/ProfileData/InstrProfData.inc"
+  };
+
+  auto *DataTy = StructType::get(Ctx, ArrayRef(DataTypes));
+
+  // Used by INSTR_PROF_VTABLE_DATA MACRO
+  Constant *VTableAddr = getVTableAddrForProfData(GV);
+  StringRef VTableName = GV->getName();
+  StringRef PGOVTableName = getPGOName(*GV);
+  // Record the length of the vtable. This is needed since vtable pointers
+  // loaded from C++ objects might be from the middle of a vtable definition.
+  uint32_t VTableSizeVal =
+      M->getDataLayout().getTypeAllocSize(GV->getValueType());
+
+  Constant *DataVals[] = {
+#define INSTR_PROF_VTABLE_DATA(Type, LLVMType, Name, Init) Init,
+#include "llvm/ProfileData/InstrProfData.inc"
+  };
+
+  auto *Data =
+      new GlobalVariable(*M, DataTy, false /* constant */, Linkage,
+                         ConstantStruct::get(DataTy, DataVals),
+                         getVarName(GV, getInstrProfVTableVarPrefix()));
+
+  Data->setVisibility(Visibility);
+  Data->setSection(getInstrProfSectionName(IPSK_vtab, TT.getObjectFormat()));
+  Data->setAlignment(Align(8));
+
+  const bool NeedComdat = needsComdatForCounter(*GV, *M);
+
+  // GV is the data structure to record vtable information.
+  // Place the global variable for per-vtable profile data in a comdat group
+  // if the associated vtable definition is a COMDAT. This makes sure only one
+  // copy of the variable for the vtable will be emitted after linking.
+  auto MaybeSetComdat = [&](GlobalVariable *GV, StringRef GroupName) {
+    bool UseComdat = (NeedComdat || TT.isOSBinFormatELF());
+    if (UseComdat) {
+      // Create a new comdat group using the name of the global variable as
+      // opposed to using the comdat group of the vtable.
+      Comdat *C = M->getOrInsertComdat(GroupName);
+      // For ELF, when not using COMDAT, put the vtable profile data into a
+      // nodeduplicate COMDAT which is lowered to a zero-flag zero group.
+      // This allows -z -start-top-gc to discard the entire group when the
----------------
snehasish wrote:

s/start-top-gc/start-stop-gc

https://github.com/llvm/llvm-project/pull/66825