[Driver][SYCL] Emit an error if c compilation is forced (#1438)

Emit an error if c compilation is forced using -x c or -x c-header when -fsycl mode is used

Signed-off-by: Harini Chilamantula <harini.chilamantula@intel.com>

Author: hchilama

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -255,6 +255,8 @@ def err_drv_expecting_fopenmp_with_fopenmp_targets : Error<
   "The option -fopenmp-targets must be used in conjunction with a -fopenmp option compatible with offloading, please use -fopenmp=libomp or -fopenmp=libiomp5.">;
 def err_drv_expecting_fsycl_with_sycl_opt : Error<
   "The option %0 must be used in conjunction with -fsycl to enable offloading.">;
+def err_drv_fsycl_with_c_type : Error<
+  "The option %0%1 must not be used in conjunction with -fsycl which expects C++ source.">;
 def warn_drv_omp_offload_target_duplicate : Warning<
   "The OpenMP offloading target '%0' is similar to target '%1' already specified - will be ignored.">,
   InGroup<OpenMPTarget>;

clang/lib/Driver/Driver.cpp

@@ -769,6 +769,15 @@ void Driver::CreateOffloadingDeviceToolChains(Compilation &C,
     }
     return SYCLArg;
   };
+
+  // Emit an error if c-compilation is forced in -fsycl mode
+  if (HasValidSYCLRuntime)
+    for (StringRef XValue : C.getInputArgs().getAllArgValues(options::OPT_x)) {
+      if (XValue == "c" || XValue == "c-header")
+        C.getDriver().Diag(clang::diag::err_drv_fsycl_with_c_type)
+            << "-x " << XValue;
+    }
+
   Arg *SYCLTargets = getArgRequiringSYCLRuntime(options::OPT_fsycl_targets_EQ);
   Arg *SYCLLinkTargets =
       getArgRequiringSYCLRuntime(options::OPT_fsycl_link_targets_EQ);

clang/test/Driver/sycl-offload.c

@@ -795,5 +795,10 @@
 // LIB-NODEVICE: 1: linker, {0}, image, (host-sycl)
 // LIB-NODEVICE-NOT: linker, {{.*}}, spirv, (device-sycl)
 
+// Checking for an error if c-compilation is forced
+// RUN: %clangxx -### -c -fsycl -xc %s 2>&1 | FileCheck -check-prefixes=CHECK_XC_FSYCL %s
+// RUN: %clangxx -### -c -fsycl -xc-header %s 2>&1 | FileCheck -check-prefixes=CHECK_XC_FSYCL %s
+// CHECK_XC_FSYCL: The option -x c{{.*}} must not be used in conjunction with -fsycl{{.*}}
+
 // TODO: SYCL specific fail - analyze and enable
 // XFAIL: windows-msvc