[Driver][SYCL] Retain comments when preprocessing for integration footer (#3918)

When generating the source file that has the integration footer appended
too, we want to retain the comments, which will improve verification
and diagnostic information.

Author: mdtoguchi

clang/lib/Driver/ToolChains/Clang.cpp

@@ -1148,6 +1148,17 @@ static void handleAMDGPUCodeObjectVersionOptions(const Driver &D,
   }
 }
 
+/// Check whether the given input tree contains any append footer actions
+static bool ContainsAppendFooterAction(const Action *A) {
+  if (isa<AppendFooterJobAction>(A))
+    return true;
+  for (const auto &AI : A->inputs())
+    if (ContainsAppendFooterAction(AI))
+      return true;
+
+  return false;
+}
+
 void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
                                     const Driver &D, const ArgList &Args,
                                     ArgStringList &CmdArgs,
@@ -1161,6 +1172,13 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
   Args.AddLastArg(CmdArgs, options::OPT_C);
   Args.AddLastArg(CmdArgs, options::OPT_CC);
 
+  // When preprocessing using the integration footer, add the comments
+  // to the first preprocessing step.
+  if (JA.isOffloading(Action::OFK_SYCL) && !ContainsAppendFooterAction(&JA) &&
+      Args.hasArg(options::OPT_fsycl_use_footer) &&
+      JA.isDeviceOffloading(Action::OFK_None))
+    CmdArgs.push_back("-C");
+
   // Handle dependency file generation.
   Arg *ArgM = Args.getLastArg(options::OPT_MM);
   if (!ArgM)
@@ -4232,17 +4250,6 @@ static bool ContainsWrapperAction(const Action *A) {
   return false;
 }
 
-/// Check whether the given input tree contains any append footer actions
-static bool ContainsAppendFooterAction(const Action *A) {
-  if (isa<AppendFooterJobAction>(A))
-    return true;
-  for (const auto &AI : A->inputs())
-    if (ContainsAppendFooterAction(AI))
-      return true;
-
-  return false;
-}
-
 // Put together an external compiler compilation call which is used instead
 // of the clang invocation for the host compile of an offload compilation.
 // Enabling command line:  clang++ -fsycl -fsycl-host-compiler=<HostExe>

clang/test/Driver/sycl-int-footer.cpp

@@ -2,7 +2,7 @@
 // RUN:  %clangxx -fsycl -fsycl-use-footer %s -### 2>&1 \
 // RUN:   | FileCheck -check-prefix FOOTER %s
 // FOOTER: clang{{.*}} "-fsycl-is-device"{{.*}} "-fsycl-int-header=[[INTHEADER:.+\.h]]" "-fsycl-int-footer=[[INTFOOTER:.+\h]]" "-sycl-std={{.*}}"
-// FOOTER: clang{{.*}} "-include" "[[INTHEADER]]"{{.*}} "-fsycl-is-host"{{.*}} "-E"{{.*}} "-o" "[[PREPROC:.+\.ii]]"
+// FOOTER: clang{{.*}} "-include" "[[INTHEADER]]"{{.*}} "-fsycl-is-host"{{.*}} "-E"{{.*}} "-C"{{.*}} "-o" "[[PREPROC:.+\.ii]]"
 // FOOTER: append-file{{.*}} "[[PREPROC]]" "--append=[[INTFOOTER]]" "--output=[[APPENDEDSRC:.+\.cpp]]"
 // FOOTER: clang{{.*}} "-fsycl-is-host"{{.*}} "[[APPENDEDSRC]]"
 // FOOTER-NOT: "-include" "[[INTHEADER]]"