[Driver][SYCL] Assertion when using -P -fsycl on Windows (#2407)

When performing preprocessing with -P on Windows, there was an
assumption that we would always be at the top level.  This is not
true when performing offloading.  Make adjustments to allow for
-P to be used with offload.

Signed-off-by: Michael D Toguchi <michael.d.toguchi@intel.com>

clang/lib/Driver/Driver.cpp

@@ -6118,8 +6118,9 @@ const char *Driver::GetNamedOutputPath(Compilation &C, const JobAction &JA,
   }
 
   // For /P, preprocess to file named after BaseInput.
-  if (C.getArgs().hasArg(options::OPT__SLASH_P)) {
-    assert(AtTopLevel && isa<PreprocessJobAction>(JA));
+  if (C.getArgs().hasArg(options::OPT__SLASH_P) &&
+      ((AtTopLevel && isa<PreprocessJobAction>(JA)) ||
+       isa<OffloadBundlingJobAction>(JA))) {
     StringRef BaseName = llvm::sys::path::filename(BaseInput);
     StringRef NameArg;
     if (Arg *A = C.getArgs().getLastArg(options::OPT__SLASH_Fi))

clang/test/Driver/sycl-offload-win.c

@@ -95,5 +95,11 @@
 // FOFFLOAD_STATIC_LIB_SRC2: llvm-link{{(.exe)?}}{{.*}} "@{{.*}}"
 // FOFFLOAD_STATIC_LIB_SRC2: link{{(.exe)?}}{{.+}} "-defaultlib:[[LIB]]"
 
+// Check for /P behaviors
+// RUN: %clang_cl --target=x86_64-pc-windows-msvc -fsycl -P %s -### 2>&1 | FileCheck -check-prefix=FSYCL_P %s
+// FSYCL_P: clang{{.*}} "-cc1" "-triple" "spir64-unknown-unknown-sycldevice" {{.*}} "-E" {{.*}} "-o" "[[DEVICEPP:.+\.i]]"
+// FSYCL_P: clang{{.*}} "-cc1" "-triple" "x86_64-pc-windows-msvc{{.*}}" {{.*}} "-E" {{.*}} "-o" "[[HOSTPP:.+\.i]]"
+// FSYCL_P: clang-offload-bundler{{.*}} "-type=i" "-targets=sycl-spir64-unknown-unknown-sycldevice,host-x86_64-pc-windows-msvc" {{.*}} "-inputs=[[DEVICEPP]],[[HOSTPP]]"
+
 // TODO: SYCL specific fail - analyze and enable
 // XFAIL: windows-msvc