[SYCL][Driver] Emit an error when PCH is triggered in SYCL mode.

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -360,6 +360,8 @@ def err_drv_expecting_fsycl_with_sycl_opt : Error<
   "'%0' must be used in conjunction with '-fsycl' to enable offloading">;
 def err_drv_fsycl_with_c_type : Error<
   "'%0' must not be used in conjunction with '-fsycl', which expects C++ source">;
+def err_drv_fsycl_with_pch : Error<
+  "Precompiled header generation is not supported with '-fsycl'">;
 def err_drv_fsycl_unsupported_with_opt
   : Error<"'%0' is not supported with '-fsycl'">;
 def err_drv_sycl_missing_amdgpu_arch : Error<

clang/lib/Driver/Driver.cpp

@@ -9252,6 +9252,11 @@ const char *Driver::GetNamedOutputPath(Compilation &C, const JobAction &JA,
     }
   }
 
+  // Emit an error if PCH(Pre-Compiled Header) file generation is forced in
+  // -fsycl mode.
+  if (C.getArgs().hasFlag(options::OPT_fsycl, options::OPT_fno_sycl, false) &&
+      JA.getType() == types::TY_PCH)
+    Diag(clang::diag::err_drv_fsycl_with_pch);
   // As an annoying special case, PCH generation doesn't strip the pathname.
   if (JA.getType() == types::TY_PCH && !IsCLMode()) {
     llvm::sys::path::remove_filename(BasePath);

clang/test/Driver/pch-fsycl-error.cpp

@@ -0,0 +1,19 @@
+// This test checks that an error is emitted when 
+// PCH(Precompiled Header) file generation is forced in -fsycl mode.
+
+// RUN: touch %t.h
+
+// Linux
+// RUN: %clang -c -fsycl -x c++-header %t.h -###  %s 2> %t1.txt
+// RUN: FileCheck %s -input-file=%t1.txt
+// CHECK: Precompiled header generation is not supported with '-fsycl'
+
+// Windows
+// RUN: %clang_cl -c -fsycl -x c++-header %t.h -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-ERROR %s
+// CHECK-ERROR: Precompiled header generation is not supported with '-fsycl'
+
+// /Yc
+// RUN: %clang_cl -fsycl /Ycpchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YC %s
+// CHECK-YC: Precompiled header generation is not supported with '-fsycl'