clang-driver: use llvm_fast_shutdown

[nhaehnle]

Summary

Avoid running almost all global destructors in the common case.

Use C->isForDiagnostics() for the decision of whether to do this, which
is the same condition as used elsewhere for triggering "-disable-free".

[efriedma]

LGTM

clang/tools/driver/driver.cpp

 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Option/OptTable.h"
 #include "llvm/Option/Option.h"
 #include "llvm/Support/BuryPointer.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/FastShutdown.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/PrettyStackTrace.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/Regex.h"
if (Tool == "-cc1gen-reproducer")
     return cc1gen_reproducer_main(makeArrayRef(ArgV).slice(2), ArgV[0],
                                   GetExecutablePathVP);
   // Reject unknown tools.
   llvm::errs() << "error: unknown integrated tool '" << Tool << "'. "
                << "Valid tools include '-cc1' and '-cc1as'.\n";
   return 1;
 }
 
-int clang_main(int Argc, char **Argv) {
-  noteBottomOfStack();
-  llvm::InitLLVM X(Argc, Argv);
-  llvm::setBugReportMsg("PLEASE submit a bug report to " BUG_REPORT_URL
-                        " and include the crash backtrace, preprocessed "
-                        "source, and associated run script.\n");
+// Return (FastShutdown, RetCode).
+//
+// Fast shutdown is implemented in the caller. We want the locals of this
+// function to be cleaned up even when fast shutdown is used, as at least the
+// driver's destructor must run to properly flush and close output streams (at
+// least the compilation database stream).
+static std::pair<bool, int> ExecuteClang(int Argc, char **Argv) {
   SmallVector<const char *, 256> Args(Argv, Argv + Argc);
 
   if (llvm::sys::Process::FixupStandardFileDescriptors())
-    return 1;
+    return {false, 1};
 
   llvm::InitializeAllTargets();
 
   llvm::BumpPtrAllocator A;
   llvm::StringSaver Saver(A);
 
   // Parse response files using the GNU syntax, unless we're in CL mode. There
   // are two ways to put clang in CL compatibility mode: Args[0] is either
static std::pair<bool, int> ExecuteClang(int Argc, char **Argv) {
   auto FirstArg = llvm::find_if(llvm::drop_begin(Args),
                                 [](const char *A) { return A != nullptr; });
   if (FirstArg != Args.end() && StringRef(*FirstArg).startswith("-cc1")) {
     // If -cc1 came from a response file, remove the EOL sentinels.
     if (MarkEOLs) {
       auto newEnd = std::remove(Args.begin(), Args.end(), nullptr);
       Args.resize(newEnd - Args.begin());
     }
-    return ExecuteCC1Tool(Args);
+    return {false, ExecuteCC1Tool(Args)};
   }
 
   // Handle options that need handling before the real command line parsing in
   // Driver::BuildCompilation()
   bool CanonicalPrefixes = true;
   for (int i = 1, size = Args.size(); i < size; ++i) {
     // Skip end-of-line response file markers
     if (Args[i] == nullptr)
auto Level = llvm::StringSwitch<Optional<Driver::ReproLevel>>(A->getValue())
                      .Case("off", Driver::ReproLevel::Off)
                      .Case("crash", Driver::ReproLevel::OnCrash)
                      .Case("error", Driver::ReproLevel::OnError)
                      .Case("always", Driver::ReproLevel::Always)
                      .Default(None);
     if (!Level) {
       llvm::errs() << "Unknown value for " << A->getSpelling() << ": '"
                    << A->getValue() << "'\n";
-      return 1;
+      return {false, 1};
     }
     ReproLevel = *Level;
   }
   if (!!::getenv("FORCE_CLANG_DIAGNOSTICS_CRASH"))
     ReproLevel = Driver::ReproLevel::Always;
 
   int Res = 1;
   bool IsCrash = false;
#ifdef _WIN32
   // Once abnormal termination was caught, negative status should not be
   // propagated.
   if (Res < 0)
     Res = 1;
 #endif
 
   // If we have multiple failing commands, we return the result of the first
   // failing command.
+  bool FastShutdown = !C->isForDiagnostics();
+  return {FastShutdown, Res};
+}
+
+int clang_main(int Argc, char **Argv) {
+  noteBottomOfStack();
+  llvm::InitLLVM X(Argc, Argv);
+  llvm::setBugReportMsg("PLEASE submit a bug report to " BUG_REPORT_URL
+                        " and include the crash backtrace, preprocessed "
+                        "source, and associated run script.\n");
+
+  bool FastShutdown;
+  int Res;
+  std::tie(FastShutdown, Res) = ExecuteClang(Argc, Argv);
+
+  if (FastShutdown) {
+    llvm::llvm_fast_shutdown();
+    llvm::sys::Process::Exit(Res, /*NoCleanup=*/true);
+  }
+
   return Res;
 }