[Clang][Driver] Re-use the calling process instead of creating a new process for the cc1 invocation

With this patch, the clang tool will now call the -cc1 invocation directly inside the same process. Previously, the -cc1 invocation was creating, and waiting for, a new process.
This patch therefore reduces the number of created processes during a build, thus it reduces build times on platforms where process creation can be costly (Windows) and/or impacted by a antivirus.
It also makes debugging a bit easier, as there's no need to attach to the secondary -cc1 process anymore, breakpoints will be hit inside the same process.

Crashes or signaling inside the -cc1 invocation will have the same side-effect as before, and will be reported through the same means.

This behavior can be controlled at compile-time through the CLANG_SPAWN_CC1 cmake flag, which defaults to OFF. Setting it to ON will revert to the previous behavior, where any -cc1 invocation will create/fork a secondary process.
At run-time, it is also possible to tweak the CLANG_SPAWN_CC1 environment variable. Setting it and will override the compile-time setting. A value of 0 calls -cc1 inside the calling process; a value of 1 will create a secondary process, as before.

Differential Revision: https://reviews.llvm.org/D69825

clang/CMakeLists.txt

@@ -237,6 +237,9 @@ set(ENABLE_X86_RELAX_RELOCATIONS OFF CACHE BOOL
 set(ENABLE_EXPERIMENTAL_NEW_PASS_MANAGER FALSE CACHE BOOL
   "Enable the experimental new pass manager by default.")
 
+set(CLANG_SPAWN_CC1 OFF CACHE BOOL
+    "Whether clang should use a new process for the CC1 invocation")
+
 # TODO: verify the values against LangStandards.def?
 set(CLANG_DEFAULT_STD_C "" CACHE STRING
   "Default standard to use for C/ObjC code (IDENT from LangStandards.def, empty for platform default)")

clang/include/clang/Config/config.h.cmake

@@ -80,4 +80,7 @@
 #cmakedefine01 CLANG_ENABLE_OBJC_REWRITER
 #cmakedefine01 CLANG_ENABLE_STATIC_ANALYZER
 
+/* Spawn a new process clang.exe for the CC1 tool invocation, when necessary */
+#cmakedefine01 CLANG_SPAWN_CC1
+
 #endif

clang/include/clang/Driver/Driver.h

@@ -204,6 +204,13 @@ public:
   /// Whether the driver is generating diagnostics for debugging purposes.
   unsigned CCGenDiagnostics : 1;
 
+  /// Pointer to the ExecuteCC1Tool function, if available.
+  /// When the clangDriver lib is used through clang.exe, this provides a
+  /// shortcut for executing the -cc1 command-line directly, in the same
+  /// process.
+  typedef int (*CC1ToolFunc)(ArrayRef<const char *> argv);
+  CC1ToolFunc CC1Main = nullptr;
+
 private:
   /// Raw target triple.
   std::string TargetTriple;

clang/include/clang/Driver/Job.h

@@ -119,7 +119,7 @@ public:
   /// \param NewEnvironment An array of environment variables.
   /// \remark If the environment remains unset, then the environment
   ///         from the parent process will be used.
-  void setEnvironment(llvm::ArrayRef<const char *> NewEnvironment);
+  virtual void setEnvironment(llvm::ArrayRef<const char *> NewEnvironment);
 
   const char *getExecutable() const { return Executable; }
 
@@ -130,6 +130,24 @@ public:
 
   /// Set whether to print the input filenames when executing.
   void setPrintInputFilenames(bool P) { PrintInputFilenames = P; }
+
+protected:
+  /// Optionally print the filenames to be compiled
+  void PrintFileNames() const;
+};
+
+/// Use the CC1 tool callback when available, to avoid creating a new process
+class CC1Command : public Command {
+public:
+  using Command::Command;
+
+  void Print(llvm::raw_ostream &OS, const char *Terminator, bool Quote,
+             CrashReportInfo *CrashInfo = nullptr) const override;
+
+  int Execute(ArrayRef<Optional<StringRef>> Redirects, std::string *ErrMsg,
+              bool *ExecutionFailed) const override;
+
+  void setEnvironment(llvm::ArrayRef<const char *> NewEnvironment) override;
 };
 
 /// Like Command, but with a fallback which is executed in case

clang/lib/Driver/Job.cpp

@@ -19,8 +19,10 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSet.h"
 #include "llvm/ADT/StringSwitch.h"
+#include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/PrettyStackTrace.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
@@ -313,38 +315,25 @@ void Command::setEnvironment(llvm::ArrayRef<const char *> NewEnvironment) {
   Environment.push_back(nullptr);
 }
 
-int Command::Execute(ArrayRef<llvm::Optional<StringRef>> Redirects,
-                     std::string *ErrMsg, bool *ExecutionFailed) const {
+void Command::PrintFileNames() const {
   if (PrintInputFilenames) {
     for (const char *Arg : InputFilenames)
       llvm::outs() << llvm::sys::path::filename(Arg) << "\n";
     llvm::outs().flush();
   }
+}
 
-  SmallVector<const char*, 128> Argv;
-
-  Optional<ArrayRef<StringRef>> Env;
-  std::vector<StringRef> ArgvVectorStorage;
-  if (!Environment.empty()) {
-    assert(Environment.back() == nullptr &&
-           "Environment vector should be null-terminated by now");
-    ArgvVectorStorage = llvm::toStringRefArray(Environment.data());
-    Env = makeArrayRef(ArgvVectorStorage);
-  }
+int Command::Execute(ArrayRef<llvm::Optional<StringRef>> Redirects,
+                     std::string *ErrMsg, bool *ExecutionFailed) const {
+  PrintFileNames();
 
+  SmallVector<const char *, 128> Argv;
   if (ResponseFile == nullptr) {
     Argv.push_back(Executable);
     Argv.append(Arguments.begin(), Arguments.end());
     Argv.push_back(nullptr);
-
-    auto Args = llvm::toStringRefArray(Argv.data());
-    return llvm::sys::ExecuteAndWait(
-        Executable, Args, Env, Redirects, /*secondsToWait*/ 0,
-        /*memoryLimit*/ 0, ErrMsg, ExecutionFailed);
-  }
-
-  // We need to put arguments in a response file (command is too large)
-  // Open stream to store the response file contents
+  } else {
+    // If the command is too large, we need to put arguments in a response file.
     std::string RespContents;
     llvm::raw_string_ostream SS(RespContents);
 
@@ -361,8 +350,20 @@ int Command::Execute(ArrayRef<llvm::Optional<StringRef>> Redirects,
         *ErrMsg = EC.message();
       if (ExecutionFailed)
         *ExecutionFailed = true;
+      // Return -1 by convention (see llvm/include/llvm/Support/Program.h) to
+      // indicate the requested executable cannot be started.
       return -1;
     }
+  }
+
+  Optional<ArrayRef<StringRef>> Env;
+  std::vector<StringRef> ArgvVectorStorage;
+  if (!Environment.empty()) {
+    assert(Environment.back() == nullptr &&
+           "Environment vector should be null-terminated by now");
+    ArgvVectorStorage = llvm::toStringRefArray(Environment.data());
+    Env = makeArrayRef(ArgvVectorStorage);
+  }
 
   auto Args = llvm::toStringRefArray(Argv.data());
   return llvm::sys::ExecuteAndWait(Executable, Args, Env, Redirects,
@@ -370,6 +371,47 @@ int Command::Execute(ArrayRef<llvm::Optional<StringRef>> Redirects,
                                    /*memoryLimit*/ 0, ErrMsg, ExecutionFailed);
 }
 
+void CC1Command::Print(raw_ostream &OS, const char *Terminator, bool Quote,
+                       CrashReportInfo *CrashInfo) const {
+  OS << " (in-process)";
+  Command::Print(OS, Terminator, Quote, CrashInfo);
+}
+
+int CC1Command::Execute(ArrayRef<llvm::Optional<StringRef>> /*Redirects*/,
+                        std::string *ErrMsg, bool *ExecutionFailed) const {
+  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;
+
+  const void *PrettyState = llvm::SavePrettyStackState();
+  const Driver &D = getCreator().getToolChain().getDriver();
+
+  int R = 0;
+  // Enter ExecuteCC1Tool() instead of starting up a new process
+  if (!CRC.RunSafely([&]() { R = D.CC1Main(Argv); })) {
+    llvm::RestorePrettyStackState(PrettyState);
+    return CRC.RetCode;
+  }
+  return R;
+}
+
+void CC1Command::setEnvironment(llvm::ArrayRef<const char *> NewEnvironment) {
+  // We don't support set a new environment when calling into ExecuteCC1Tool()
+  llvm_unreachable(
+      "The CC1Command doesn't support changing the environment vars!");
+}
+
 FallbackCommand::FallbackCommand(const Action &Source_, const Tool &Creator_,
                                  const char *Executable_,
                                  const llvm::opt::ArgStringList &Arguments_,

clang/lib/Driver/ToolChains/Clang.cpp

@@ -5979,6 +5979,10 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     // fails, so that the main compilation's fallback to cl.exe runs.
     C.addCommand(std::make_unique<ForceSuccessCommand>(JA, *this, Exec,
                                                         CmdArgs, Inputs));
+  } else if (D.CC1Main && !D.CCGenDiagnostics) {
+    // Invoke the CC1 directly in this process
+    C.addCommand(
+        std::make_unique<CC1Command>(JA, *this, Exec, CmdArgs, Inputs));
   } else {
     C.addCommand(std::make_unique<Command>(JA, *this, Exec, CmdArgs, Inputs));
   }

clang/test/CMakeLists.txt

@@ -13,6 +13,7 @@ llvm_canonicalize_cmake_booleans(
   CLANG_BUILD_EXAMPLES
   CLANG_ENABLE_ARCMT
   CLANG_ENABLE_STATIC_ANALYZER
+  CLANG_SPAWN_CC1
   ENABLE_BACKTRACES
   ENABLE_EXPERIMENTAL_NEW_PASS_MANAGER
   LLVM_ENABLE_ZLIB

clang/test/Driver/cc1-spawnprocess.c

@@ -0,0 +1,4 @@
+// RUN: env -u CLANG_SPAWN_CC1 %clang -c %s -o /dev/null
+// RUN: env CLANG_SPAWN_CC1=0 %clang -c %s -o /dev/null
+// RUN: env CLANG_SPAWN_CC1=1 %clang -c %s -o /dev/null
+// RUN: env CLANG_SPAWN_CC1=test not %clang -c %s -o /dev/null

clang/test/Driver/clang_f_opts.c

@@ -493,7 +493,7 @@
 // RUN: %clang -target x86_64-unknown-none-none -### -fno-short-wchar -fshort-wchar %s 2>&1 | FileCheck -check-prefix=CHECK-WCHAR2 -check-prefix=DELIMITERS %s
 // Make sure we don't match the -NOT lines with the linker invocation.
 // Delimiters match the start of the cc1 and the start of the linker lines
-// DELIMITERS: {{^ *"}}
+// DELIMITERS: {{^ (\(in-process\)|")}}
 // CHECK-WCHAR1: -fwchar-type=int
 // CHECK-WCHAR1-NOT: -fwchar-type=short
 // CHECK-WCHAR2: -fwchar-type=short

clang/test/Driver/fsanitize-blacklist.c

@@ -6,7 +6,7 @@
 // Make sure we don't match the -NOT lines with the linker invocation.
 // Delimiters match the start of the cc1 and the start of the linker lines
 // for fragile tests.
-// DELIMITERS: {{^ *"}}
+// DELIMITERS: {{^ (\(in-process\)|")}}
 
 // RUN: echo "fun:foo" > %t.good
 // RUN: echo "fun:bar" > %t.second

clang/test/Driver/unknown-arg.c

@@ -54,7 +54,7 @@
 // SILENT-NOT: warning:
 // CC1AS-DID-YOU-MEAN: error: unknown argument '-hell'; did you mean '-help'?
 // CC1AS-DID-YOU-MEAN: error: unknown argument '--version'; did you mean '-version'?
-// UNKNOWN-INTEGRATED: error: unknown integrated tool 'asphalt'. Valid tools include '-cc1' and '-cc1as'.
+// UNKNOWN-INTEGRATED: error: unknown integrated tool '-cc1asphalt'. Valid tools include '-cc1' and '-cc1as'.
 
 // RUN: %clang -S %s -o %t.s  -Wunknown-to-clang-option 2>&1 | FileCheck --check-prefix=IGNORED %s
 

clang/test/Driver/warning-options_pedantic.cpp

@@ -1,6 +1,6 @@
 // Make sure we don't match the -NOT lines with the linker invocation.
 // Delimiters match the start of the cc1 and the start of the linker lines
-// DELIMITERS: {{^ *"}}
+// DELIMITERS: {{^ (\(in-process\)|")}}
 
 // RUN: %clang -### -pedantic -no-pedantic %s 2>&1 | FileCheck -check-prefix=NO_PEDANTIC -check-prefix=DELIMITERS %s
 // RUN: %clang -### -pedantic -Wno-pedantic %s 2>&1 | FileCheck -check-prefix=PEDANTIC -check-prefix=DELIMITERS %s

clang/tools/driver/driver.cpp

@@ -14,6 +14,7 @@
 #include "clang/Driver/Driver.h"
 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Basic/Stack.h"
+#include "clang/Config/config.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
@@ -30,6 +31,7 @@
 #include "llvm/Option/OptTable.h"
 #include "llvm/Option/Option.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Host.h"
@@ -239,6 +241,8 @@ static void getCLEnvVarOptions(std::string &EnvValue, llvm::StringSaver &Saver,
       *NumberSignPtr = '=';
 }
 
+static int ExecuteCC1Tool(ArrayRef<const char *> argv);
+
 static void SetBackdoorDriverOutputsFromEnvVars(Driver &TheDriver) {
   // Handle CC_PRINT_OPTIONS and CC_PRINT_OPTIONS_FILE.
   TheDriver.CCPrintOptions = !!::getenv("CC_PRINT_OPTIONS");
@@ -254,6 +258,27 @@ static void SetBackdoorDriverOutputsFromEnvVars(Driver &TheDriver) {
   TheDriver.CCLogDiagnostics = !!::getenv("CC_LOG_DIAGNOSTICS");
   if (TheDriver.CCLogDiagnostics)
     TheDriver.CCLogDiagnosticsFilename = ::getenv("CC_LOG_DIAGNOSTICS_FILE");
+
+  // Whether the cc1 tool should be called inside the current process, or if we
+  // should spawn a new clang process (old behavior).
+  // Not having an additional process saves some execution time of Windows,
+  // and makes debugging easier.
+  bool UseNewCC1Process = CLANG_SPAWN_CC1;
+
+  StringRef SpawnCC1Str = ::getenv("CLANG_SPAWN_CC1");
+  if (!SpawnCC1Str.empty()) {
+    if (SpawnCC1Str != "0" && SpawnCC1Str != "1") {
+      llvm::errs() << "error: the value of the environment variable "
+                      "CLANG_SPAWN_CC1 must be either 0 or 1.\n";
+      ::exit(1);
+    }
+    UseNewCC1Process = SpawnCC1Str[0] - '0';
+  }
+  if (!UseNewCC1Process) {
+    TheDriver.CC1Main = &ExecuteCC1Tool;
+    // Ensure the CC1Command actually catches cc1 crashes
+    llvm::CrashRecoveryContext::Enable();
+  }
 }
 
 static void FixupDiagPrefixExeName(TextDiagnosticPrinter *DiagClient,
@@ -303,13 +328,19 @@ static void SetInstallDir(SmallVectorImpl<const char *> &argv,
     TheDriver.setInstalledDir(InstalledPathParent);
 }
 
-static int ExecuteCC1Tool(ArrayRef<const char *> argv, StringRef Tool) {
+static int ExecuteCC1Tool(ArrayRef<const char *> argv) {
+  // If we call the cc1 tool from the clangDriver library (through
+  // Driver::CC1Main), we need to cleanup the options usage count. The options
+  // are currently global, and they might have been used previously by the
+  // driver.
+  llvm::cl::ResetAllOptionOccurrences();
+  StringRef Tool = argv[1];
   void *GetExecutablePathVP = (void *)(intptr_t) GetExecutablePath;
-  if (Tool == "")
+  if (Tool == "-cc1")
     return cc1_main(argv.slice(2), argv[0], GetExecutablePathVP);
-  if (Tool == "as")
+  if (Tool == "-cc1as")
     return cc1as_main(argv.slice(2), argv[0], GetExecutablePathVP);
-  if (Tool == "gen-reproducer")
+  if (Tool == "-cc1gen-reproducer")
     return cc1gen_reproducer_main(argv.slice(2), argv[0], GetExecutablePathVP);
 
   // Reject unknown tools.
@@ -379,7 +410,7 @@ int main(int argc_, const char **argv_) {
       auto newEnd = std::remove(argv.begin(), argv.end(), nullptr);
       argv.resize(newEnd - argv.begin());
     }
-    return ExecuteCC1Tool(argv, argv[1] + 4);
+    return ExecuteCC1Tool(argv);
   }
 
   bool CanonicalPrefixes = true;
@@ -503,7 +534,7 @@ int main(int argc_, const char **argv_) {
 
 #ifdef _WIN32
   // Exit status should not be negative on Win32, unless abnormal termination.
-  // Once abnormal termiation was caught, negative status should not be
+  // Once abnormal termination was caught, negative status should not be
   // propagated.
   if (Res < 0)
     Res = 1;