[clang] [compiler-rt] [llvm] [InstrFDO][TypeProf] Implement binary instrumentation and profile read/write (PR #66825)

[Snehasish Kumar via cfe-commits]

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@@ -1237,6 +1259,101 @@ void InstrLowerer::maybeSetComdat(GlobalVariable *GV, Function *Fn,
     GV->setLinkage(GlobalValue::InternalLinkage);
 }
 
+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: Introduce an internal alias like what's done for functions to reduce
+// the number of relocation entries.
+static inline Constant *getVTableAddrForProfData(GlobalVariable *GV) {
+  auto *Int8PtrTy = PointerType::getUnqual(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);
+}
+
+void InstrLowerer::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.") ||
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snehasish wrote:

Add a comment to explain this if condition.

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