message: [lldb] Reland "Refactor guard variable checks in IRForTarget"
  It seems the broken guard variable check for Windows was a feature(TM)
  and not a bug, so let's keep add a flag to the guard check that keeps
  the old behavior in the places where we ignored guard variables before.
diff: @@ -155,6 +155,15 @@ clang::NamedDecl *IRForTarget::DeclForGlobal(GlobalValue *global_val) {
  return DeclForGlobal(global_val, m_module);
  }
  +/// Returns true iff the mangled symbol is for a static guard variable.
  +static bool isGuardVariableSymbol(llvm::StringRef mangled_symbol,
  + bool check_ms_abi = true) {
  + bool result = mangled_symbol.startswith("_ZGV"); // Itanium ABI guard variable
  + if (check_ms_abi)
  + result |= mangled_symbol.startswith("@4IA"); // Microsoft ABI
  + return result;
  +}
  +
  bool IRForTarget::CreateResultVariable(llvm::Function &llvm_function) {
  lldb_private::Log *log(
  lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_EXPRESSIONS));
  @@ -172,15 +181,17 @@ bool IRForTarget::CreateResultVariable(llvm::Function &llvm_function) {
  for (StringMapEntry<llvm::Value *> &value_symbol : value_symbol_table) {
  result_name = value_symbol.first();
  - if (result_name.contains("$__lldb_expr_result_ptr") &&
  - !result_name.startswith("_ZGV")) {
  + // Check if this is a guard variable. It seems this causes some hiccups
  + // on Windows, so let's only check for Itanium guard variables.
  + bool is_guard_var = isGuardVariableSymbol(result_name, /*MS ABI*/ false);
  +
  + if (result_name.contains("$__lldb_expr_result_ptr") && !is_guard_var) {
  found_result = true;
  m_result_is_pointer = true;
  break;
  }
  - if (result_name.contains("$__lldb_expr_result") &&
  - !result_name.startswith("_ZGV")) {
  + if (result_name.contains("$__lldb_expr_result") && !is_guard_var) {
  found_result = true;
  m_result_is_pointer = false;
  break;
  @@ -1528,14 +1539,12 @@ bool IRForTarget::ResolveExternals(Function &llvm_function) {
  }
  static bool isGuardVariableRef(Value *V) {
  - Constant *Old = nullptr;
  + Constant *Old = dyn_cast<Constant>(V);
  - if (!(Old = dyn_cast<Constant>(V)))
  + if (!Old)
  return false;
  - ConstantExpr *CE = nullptr;
  -
  - if ((CE = dyn_cast<ConstantExpr>(V))) {
  + if (auto CE = dyn_cast<ConstantExpr>(V)) {
  if (CE->getOpcode() != Instruction::BitCast)
  return false;
  @@ -1544,12 +1553,8 @@ static bool isGuardVariableRef(Value *V) {
  GlobalVariable *GV = dyn_cast<GlobalVariable>(Old);
  - if (!GV || !GV->hasName() ||
  - (!GV->getName().startswith("_ZGV") && // Itanium ABI guard variable
  - !GV->getName().endswith("@4IA"))) // Microsoft ABI guard variable
  - {
  + if (!GV || !GV->hasName() || !isGuardVariableSymbol(GV->getName()))
  return false;
  - }
  return true;
  }
  