[clang][driver] Introduce new -fdriver-only flag

This patch introduces the new -fdriver-only flag which instructs Clang to only execute the driver logic without running individual jobs. In a way, this is very similar to -###, with the following differences:
 * it doesn't automatically print all jobs,
 * it doesn't avoid side effects (e.g. it will generate compilation database when -MJ is specified).

This flag will be useful in testing D121997.

Reviewed By: dexonsmith, egorzhdan

Differential Revision: https://reviews.llvm.org/D127408

1 files changed, 8 insertions, 3 deletions

diff --git a/clang/lib/Driver/Compilation.cpp b/clang/lib/Driver/Compilation.cpp
index 67d941c..b4367a0 100644
--- a/clang/lib/Driver/Compilation.cpp
+++ b/clang/lib/Driver/Compilation.cpp
@@ -162,7 +162,8 @@ bool Compilation::CleanupFileMap(const ArgStringMap &Files,
 }
 
 int Compilation::ExecuteCommand(const Command &C,
-                                const Command *&FailingCommand) const {
+                                const Command *&FailingCommand,
+                                bool LogOnly) const {
   if ((getDriver().CCPrintOptions ||
        getArgs().hasArg(options::OPT_v)) && !getDriver().CCGenDiagnostics) {
     raw_ostream *OS = &llvm::errs();
@@ -191,6 +192,9 @@ int Compilation::ExecuteCommand(const Command &C,
     C.Print(*OS, "\n", /*Quote=*/getDriver().CCPrintOptions);
   }
 
+  if (LogOnly)
+    return 0;
+
   std::string Error;
   bool ExecutionFailed;
   int Res = C.Execute(Redirects, &Error, &ExecutionFailed);
@@ -237,7 +241,8 @@ static bool InputsOk(const Command &C,
 }
 
 void Compilation::ExecuteJobs(const JobList &Jobs,
-                              FailingCommandList &FailingCommands) const {
+                              FailingCommandList &FailingCommands,
+                              bool LogOnly) const {
   // According to UNIX standard, driver need to continue compiling all the
   // inputs on the command line even one of them failed.
   // In all but CLMode, execute all the jobs unless the necessary inputs for the
@@ -246,7 +251,7 @@ void Compilation::ExecuteJobs(const JobList &Jobs,
     if (!InputsOk(Job, FailingCommands))
       continue;
     const Command *FailingCommand = nullptr;
-    if (int Res = ExecuteCommand(Job, FailingCommand)) {
+    if (int Res = ExecuteCommand(Job, FailingCommand, LogOnly)) {
       FailingCommands.push_back(std::make_pair(Res, FailingCommand));
       // Bail as soon as one command fails in cl driver mode.
       if (TheDriver.IsCLMode())