[Clang] Own the CommandLineArgs in CodeGenOptions

[aganea]

Summary

As reported in PR52704: https://github.com/llvm/llvm-project/issues/52704

Since the round-tripping generates function-local arguments, before this patch accessing CodeGenOptions.CommandLineArgs or MCTargetOptions.CommandLineArgs used to keep references on free'd data.

+@hans for the CC1Command change which otherwise blocks the usage append_range. This was unconsistent with how CommandLineArgs were passed around in other places (without the terminating nullptr element).

[jansvoboda11]

LGTM!

[aganea]

clang/lib/Driver/Job.cpp

390

I changed this to match the behavior of the main function, ie. argv[argc] is guaranteed to be a null pointer. Please let me know if you disagree.

[aheejin]

clang/lib/Driver/Job.cpp

389–390

If we push nullptr and then pop it right after that, why do we push it in the first place?

[aganea]

clang/lib/Driver/Job.cpp

389–390

Simply to guarantee that we will have a nullptr element after the end of the container. .pop_back() only decrements the size, the nullptr value will remain there.

[aganea]

clang/lib/Driver/Job.cpp

389–390

Frankly a better fix would be to change the API of ExecuteCC1Tool to take an ArrayRef and not rely on internal behavior of SmallVector. Maybe we should do that.

clang/include/clang/Basic/CodeGenOptions.h

public:
   /// Name of the stack usage file (i.e., .su file) if user passes
   /// -fstack-usage. If empty, it can be implied that -fstack-usage is not
   /// passed on the command line.
   std::string StackUsageOutput;
 
   /// Executable and command-line used to create a given CompilerInvocation.
   /// Most of the time this will be the full -cc1 command.
   const char *Argv0 = nullptr;
-  ArrayRef<const char *> CommandLineArgs;
+  std::vector<std::string> CommandLineArgs;
 
   /// The minimum hotness value a diagnostic needs in order to be included in
   /// optimization diagnostics.
   ///
   /// The threshold is an Optional value, which maps to one of the 3 states:
   /// 1. 0            => threshold disabled. All remarks will be printed.
   /// 2. positive int => manual threshold by user. Remarks with hotness exceed
   ///                    threshold will be printed.

clang/lib/Driver/Job.cpp

int CC1Command::Execute(ArrayRef<llvm::Optional<StringRef>> Redirects,
   // out-of-process execution. See discussion in https://reviews.llvm.org/D74447
   if (!InProcess)
     return Command::Execute(Redirects, ErrMsg, ExecutionFailed);
 
   PrintFileNames();
 
   SmallVector<const char *, 128> Argv;
   Argv.push_back(getExecutable());
   Argv.append(getArguments().begin(), getArguments().end());
-  Argv.push_back(nullptr);
 
   // This flag simply indicates that the program couldn't start, which isn't
   // applicable here.
   if (ExecutionFailed)
     *ExecutionFailed = false;
 
   llvm::CrashRecoveryContext CRC;
   CRC.DumpStackAndCleanupOnFailure = true;
 

clang/lib/Frontend/CompilerInvocation.cpp

bool CompilerInvocation::CreateFromArgsImpl(
   if (Res.getCodeGenOpts().FineGrainedBitfieldAccesses &&
       !Res.getLangOpts()->Sanitize.empty()) {
     Res.getCodeGenOpts().FineGrainedBitfieldAccesses = false;
     Diags.Report(diag::warn_drv_fine_grained_bitfield_accesses_ignored);
   }
 
   // Store the command-line for using in the CodeView backend.
   Res.getCodeGenOpts().Argv0 = Argv0;
-  Res.getCodeGenOpts().CommandLineArgs = CommandLineArgs;
+  append_range(Res.getCodeGenOpts().CommandLineArgs, CommandLineArgs);
 
   FixupInvocation(Res, Diags, Args, DashX);
 
   return Diags.getNumErrors() == NumErrorsBefore;
 }
 
 bool CompilerInvocation::CreateFromArgs(CompilerInvocation &Invocation,
                                         ArrayRef<const char *> CommandLineArgs,

llvm/include/llvm/MC/MCTargetOptions.h

public:
   bool Dwarf64 : 1;
   int DwarfVersion = 0;
 
   std::string ABIName;
   std::string AssemblyLanguage;
   std::string SplitDwarfFile;
 
   const char *Argv0 = nullptr;
-  ArrayRef<const char *> CommandLineArgs;
+  ArrayRef<std::string> CommandLineArgs;
 
   /// Additional paths to search for `.include` directives when using the
   /// integrated assembler.
   std::vector<std::string> IASSearchPaths;
 
   MCTargetOptions();
 
   /// getABIName - If this returns a non-empty string this represents the