[Driver] Set the default clang driver mode based on the executable

[zturner]

Summary

If --driver-mode is passed in one or more times, it will overwrite the default by this patch. This patch only makes it so that if NO --driver-mode is passed in, we try to do better than saying "must be GCC".

This is one of two steps necessary to get clang-tidy working on Windows. However, despite that, this change seems correct even in the general sense. If a --driver-mode option is not passed in, we should make the most informed possible decision we can.

[rnk]

lgtm

include/clang/Driver/Driver.h

typedef SmallVector<std::pair<types::ID, const llvm::opt::Arg *>, 16>
       InputList;
 
   /// Whether the driver should follow g++ like behavior.
   bool CCCIsCXX() const { return Mode == GXXMode; }
 
   /// Whether the driver is just the preprocessor.
   bool CCCIsCPP() const { return Mode == CPPMode; }
 
+  /// Whether the driver should follow gcc like behavior.
+  bool CCCIsCC() const { return Mode == GCCMode; }
+
   /// Whether the driver should follow cl.exe like behavior.
   bool IsCLMode() const { return Mode == CLMode; }
 
   /// Only print tool bindings, don't build any jobs.
   unsigned CCCPrintBindings : 1;
 
   /// Set CC_PRINT_OPTIONS mode, which is like -v but logs the commands to
   /// CCPrintOptionsFilename or to stderr.
public:
   /// indicate an error condition, the diagnostics should be queried
   /// to determine if an error occurred.
   Compilation *BuildCompilation(ArrayRef<const char *> Args);
 
   /// @name Driver Steps
   /// @{
 
   /// ParseDriverMode - Look for and handle the driver mode option in Args.
-  void ParseDriverMode(ArrayRef<const char *> Args);
+  void ParseDriverMode(StringRef ProgramName, ArrayRef<const char *> Args);
 
   /// ParseArgStrings - Parse the given list of strings into an
   /// ArgList.
   llvm::opt::InputArgList ParseArgStrings(ArrayRef<const char *> Args);
 
   /// BuildInputs - Construct the list of inputs and their types from 
   /// the given arguments.
   ///
public:
 
   /// Returns true if we are performing any kind of LTO.
   bool isUsingLTO() const { return LTOMode != LTOK_None; }
 
   /// Get the specific kind of LTO being performed.
   LTOKind getLTOMode() const { return LTOMode; }
 
 private:
+  /// Set the driver mode (cl, gcc, etc) from an option string of the form
+  /// --driver-mode=<mode>.
+  void setDriverModeFromOption(StringRef Opt);
+
   /// Parse the \p Args list for LTO options and record the type of LTO
   /// compilation based on which -f(no-)?lto(=.*)? option occurs last.
   void setLTOMode(const llvm::opt::ArgList &Args);
 
   /// \brief Retrieves a ToolChain for a particular \p Target triple.
   ///
   /// Will cache ToolChains for the life of the driver object, and create them
   /// on-demand.

lib/Driver/Driver.cpp

 }
 
 Driver::~Driver() {
   delete Opts;
 
   llvm::DeleteContainerSeconds(ToolChains);
 }
 
-void Driver::ParseDriverMode(ArrayRef<const char *> Args) {
-  const std::string OptName =
-      getOpts().getOption(options::OPT_driver_mode).getPrefixedName();
+void Driver::ParseDriverMode(StringRef ProgramName,
+                             ArrayRef<const char *> Args) {
+  auto Default = ToolChain::getTargetAndModeFromProgramName(ProgramName);
+  StringRef DefaultMode(Default.second);
+  setDriverModeFromOption(DefaultMode);
 
   for (const char *ArgPtr : Args) {
     // Ingore nullptrs, they are response file's EOL markers
     if (ArgPtr == nullptr)
       continue;
     const StringRef Arg = ArgPtr;
-    if (!Arg.startswith(OptName))
-      continue;
+    setDriverModeFromOption(Arg);
+  }
+}
+
+void Driver::setDriverModeFromOption(StringRef Opt) {
+  const std::string OptName =
+      getOpts().getOption(options::OPT_driver_mode).getPrefixedName();
+  if (!Opt.startswith(OptName))
+    return;
+  StringRef Value = Opt.drop_front(OptName.size());
 
-    const StringRef Value = Arg.drop_front(OptName.size());
-    const unsigned M = llvm::StringSwitch<unsigned>(Value)
-                           .Case("gcc", GCCMode)
-                           .Case("g++", GXXMode)
-                           .Case("cpp", CPPMode)
-                           .Case("cl", CLMode)
-                           .Default(~0U);
 
-    if (M != ~0U)
-      Mode = static_cast<DriverMode>(M);
-    else
-      Diag(diag::err_drv_unsupported_option_argument) << OptName << Value;
-  }
-}
 
 InputArgList Driver::ParseArgStrings(ArrayRef<const char *> ArgStrings) {
   llvm::PrettyStackTraceString CrashInfo("Command line argument parsing");
 
   unsigned IncludedFlagsBitmask;
   unsigned ExcludedFlagsBitmask;
   std::tie(IncludedFlagsBitmask, ExcludedFlagsBitmask) =
       getIncludeExcludeOptionFlagMasks();
while (!CompilerPath.empty()) {
           CompilerPath.split(llvm::sys::EnvPathSeparator);
       PrefixDirs.push_back(Split.first);
       CompilerPath = Split.second;
     }
   }
 
   // We look for the driver mode option early, because the mode can affect
   // how other options are parsed.
-  ParseDriverMode(ArgList.slice(1));
+  ParseDriverMode(ClangExecutable, ArgList.slice(1));
 
   // FIXME: What are we going to do with -V and -b?
 
   // FIXME: This stuff needs to go into the Compilation, not the driver.
   bool CCCPrintPhases;
 
   InputArgList Args = ParseArgStrings(ArgList.slice(1));
 

unittests/Driver/ToolChainTest.cpp

EXPECT_EQ("Found candidate GCC installation: "
             "/home/test/lib/gcc/arm-linux-gnueabi/4.6.1\n"
             "Selected GCC installation: "
             "/home/test/bin/../lib/gcc/arm-linux-gnueabi/4.6.1\n"
             "Candidate multilib: .;@m32\n"
             "Selected multilib: .;@m32\n",
             S);
 }
 
+TEST(ToolChainTest, DefaultDriverMode) {
+  IntrusiveRefCntPtr<DiagnosticOptions> DiagOpts = new DiagnosticOptions();
+
+  IntrusiveRefCntPtr<DiagnosticIDs> DiagID(new DiagnosticIDs());
+  struct TestDiagnosticConsumer : public DiagnosticConsumer {};
+  DiagnosticsEngine Diags(DiagID, &*DiagOpts, new TestDiagnosticConsumer);
+  IntrusiveRefCntPtr<vfs::InMemoryFileSystem> InMemoryFileSystem(
+      new vfs::InMemoryFileSystem);
+
+  Driver CCDriver("/home/test/bin/clang", "arm-linux-gnueabi", Diags,
+                  InMemoryFileSystem);
+  Driver CXXDriver("/home/test/bin/clang++", "arm-linux-gnueabi", Diags,
+                   InMemoryFileSystem);
+  Driver CLDriver("/home/test/bin/clang-cl", "arm-linux-gnueabi", Diags,
+                  InMemoryFileSystem);
+
+  std::unique_ptr<Compilation> CC(CCDriver.BuildCompilation({"foo.cpp"}));
+  std::unique_ptr<Compilation> CXX(CXXDriver.BuildCompilation({"foo.cpp"}));
+  std::unique_ptr<Compilation> CL(CLDriver.BuildCompilation({"foo.cpp"}));
+
+  EXPECT_TRUE(CCDriver.CCCIsCC());
+  EXPECT_TRUE(CXXDriver.CCCIsCXX());
+  EXPECT_TRUE(CLDriver.IsCLMode());
+}
+
 } // end anonymous namespace