[clang][LLVM Demangler] Add a diagnostic that validates that all mang…

clang/include/clang/Basic/CodeGenOptions.def

@@ -462,6 +462,9 @@ ENUM_CODEGENOPT(ZeroCallUsedRegs, llvm::ZeroCallUsedRegs::ZeroCallUsedRegsKind,
 /// non-deleting destructors. (No effect on Microsoft ABI.)
 CODEGENOPT(CtorDtorReturnThis, 1, 0)
 
+/// Whether to issue a diagnostic if a produced mangled name can not be demangled with the LLVM demangler.
+CODEGENOPT(DiagnosticsDemanglerFailures, 1, 0)
+
 /// FIXME: Make DebugOptions its own top-level .def file.
 #include "DebugOptions.def"
 

clang/include/clang/Basic/DiagnosticFrontendKinds.td

@@ -384,4 +384,8 @@ def warn_hlsl_langstd_minimal :
   Warning<"support for HLSL language version %0 is incomplete, "
           "recommend using %1 instead">,
   InGroup<HLSLDXCCompat>;
+
+def warn_name_cannot_be_demangled : Warning<
+  "cannot demangle the name '%0'">,
+  InGroup<Demangler>;
 }

clang/include/clang/Basic/DiagnosticGroups.td

@@ -1582,3 +1582,6 @@ def ExtractAPIMisuse : DiagGroup<"extractapi-misuse">;
 // Warnings about using the non-standard extension having an explicit specialization
 // with a storage class specifier.
 def ExplicitSpecializationStorageClass : DiagGroup<"explicit-specialization-storage-class">;
+
+// Diagnostics related to the LLVM demangler.
+def Demangler: DiagGroup<"demangler">;

clang/include/clang/Driver/Options.td

@@ -1967,6 +1967,10 @@ def fclang_abi_compat_EQ : Joined<["-"], "fclang-abi-compat=">, Group<f_clang_Gr
   Visibility<[ClangOption, CC1Option]>,
   MetaVarName<"<version>">, Values<"<major>.<minor>,latest">,
   HelpText<"Attempt to match the ABI of Clang <version>">;
+def fdiagnostics_demangler_failures: Flag<["-"], "fdiagnostics-demangler-failures">, Group<f_clang_Group>,
+  Visibility<[ClangOption, CC1Option]>,
+  HelpText<"Produce a diagnostic if clang cannot demangle a mangled name it generates">,
+  MarshallingInfoFlag<CodeGenOpts<"DiagnosticsDemanglerFailures">>;
 def fclasspath_EQ : Joined<["-"], "fclasspath=">, Group<f_Group>;
 def fcolor_diagnostics : Flag<["-"], "fcolor-diagnostics">, Group<f_Group>,
 

clang/lib/CodeGen/CodeGenModule.cpp

@@ -54,6 +54,7 @@
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/BinaryFormat/ELF.h"
+#include "llvm/Demangle/Demangle.h"
 #include "llvm/Frontend/OpenMP/OMPIRBuilder.h"
 #include "llvm/IR/AttributeMask.h"
 #include "llvm/IR/CallingConv.h"
@@ -2044,6 +2045,14 @@ StringRef CodeGenModule::getMangledName(GlobalDecl GD) {
                  GD.getWithKernelReferenceKind(KernelReferenceKind::Kernel),
                  ND));
 
+  if (getContext().getLangOpts().getClangABICompat() >
+      LangOptions::ClangABI::Ver19) {
+    if (llvm::isMangledName(MangledName) &&
+        llvm::demangle(MangledName) == MangledName)
+      Diags.Report(ND->getLocation(), diag::warn_name_cannot_be_demangled)
+          << MangledName;
+  }
+
   auto Result = Manglings.insert(std::make_pair(MangledName, GD));
   return MangledDeclNames[CanonicalGD] = Result.first->first();
 }

clang/lib/Driver/ToolChains/Clang.cpp

@@ -4444,6 +4444,9 @@ static void RenderDiagnosticsOptions(const Driver &D, const ArgList &Args,
 
   Args.addOptOutFlag(CmdArgs, options::OPT_fspell_checking,
                      options::OPT_fno_spell_checking);
+
+  if (Args.hasArg(options::OPT_fdiagnostics_demangler_failures))
+    CmdArgs.push_back("-fdiagnostics-demangler-failures");
 }
 
 DwarfFissionKind tools::getDebugFissionKind(const Driver &D,

clang/test/CodeGenCXX/warn-demangling-failure.cpp

@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -emit-llvm -fdemangling-failures -triple %itanium_abi_triple -o - %s | FileCheck %s
+template <class F> void parallel_loop(F &&f) { f(0); }
+
+//CHECK-LABEL: @main
+int main() {
+  int x;
+  parallel_loop([&](auto y) { // expected-warning {{cannot demangle the name '_ZZ4mainENK3$_0clIiEEDaT_'}}
+#pragma clang __debug captured
+    {
+      x = y;
+    };
+  });
+}

llvm/include/llvm/Demangle/Demangle.h

@@ -67,6 +67,13 @@ char *dlangDemangle(std::string_view MangledName);
 /// demangling occurred.
 std::string demangle(std::string_view MangledName);
 
+/// Determines if the argument string is a valid mangled name known to the
+/// demangler.
+/// \param Name - reference to a string that is potentially a mangled name.
+/// \returns - true if the argument represents a valid mangled name, false
+/// otherwise.
+bool isMangledName(std::string_view Name);
+
 bool nonMicrosoftDemangle(std::string_view MangledName, std::string &Result,
                           bool CanHaveLeadingDot = true,
                           bool ParseParams = true);

llvm/lib/Demangle/Demangle.cpp

@@ -47,6 +47,15 @@ static bool isRustEncoding(std::string_view S) { return starts_with(S, "_R"); }
 
 static bool isDLangEncoding(std::string_view S) { return starts_with(S, "_D"); }
 
+static bool isMicrosoftEncoding(std::string_view S) {
+  return starts_with(S, '?');
+}
+
+bool llvm::isMangledName(std::string_view Name) {
+  return isItaniumEncoding(Name) || isRustEncoding(Name) ||
+         isDLangEncoding(Name) || isMicrosoftEncoding(Name);
+}
+
 bool llvm::nonMicrosoftDemangle(std::string_view MangledName,
                                 std::string &Result, bool CanHaveLeadingDot,
                                 bool ParseParams) {