[SYCL][Driver] Enable PCH inclusion while performing host compilation with -fsycl (#9864)

This PR allows users to include a Pre-Compiled header (PCH) file while
performing the host compilation step with `-fsycl`.

**// Create PCH**
`clang++ -x c-header test.h`

**// Use PCH**
```
clang++ -c -fsycl -include test.h test.cpp
clang++ -c -fsycl -include-pch test.h.gch test.cpp
```

Author: srividya-sundaram

clang/lib/Driver/ToolChains/Clang.cpp

@@ -1119,6 +1119,8 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
                                     const InputInfoList &Inputs) const {
   const bool IsIAMCU = getToolChain().getTriple().isOSIAMCU();
   const bool IsIntelFPGA = Args.hasArg(options::OPT_fintelfpga);
+  bool SYCLDeviceCompilation = JA.isOffloading(Action::OFK_SYCL) &&
+                               JA.isDeviceOffloading(Action::OFK_SYCL);
 
   CheckPreprocessingOptions(D, Args);
 
@@ -1335,9 +1337,14 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
                        options::OPT_fno_pch_instantiate_templates, true))
         CmdArgs.push_back(Args.MakeArgString("-fpch-instantiate-templates"));
     }
+
     if (YcArg || YuArg) {
       StringRef ThroughHeader = YcArg ? YcArg->getValue() : YuArg->getValue();
-      if (!isa<PrecompileJobAction>(JA)) {
+      // If PCH file is available, include it while performing
+      // host compilation (-fsycl-is-host) in SYCL mode (-fsycl).
+      // as well as in non-sycl mode.
+
+      if (!isa<PrecompileJobAction>(JA) && !SYCLDeviceCompilation) {
         CmdArgs.push_back("-include-pch");
         CmdArgs.push_back(Args.MakeArgString(D.GetClPchPath(
             C, !ThroughHeader.empty()
@@ -1356,9 +1363,12 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
   }
 
   bool RenderedImplicitInclude = false;
+
   for (const Arg *A : Args.filtered(options::OPT_clang_i_Group)) {
-    if (A->getOption().matches(options::OPT_include) &&
-        D.getProbePrecompiled()) {
+    if ((A->getOption().matches(options::OPT_include) &&
+         D.getProbePrecompiled()) ||
+        A->getOption().matches(options::OPT_include_pch)) {
+
       // Handling of gcc-style gch precompiled headers.
       bool IsFirstImplicitInclude = !RenderedImplicitInclude;
       RenderedImplicitInclude = true;
@@ -1378,8 +1388,11 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
           FoundPCH = true;
         }
       }
+      // If PCH file is available, include it while performing
+      // host compilation (-fsycl-is-host) in SYCL mode (-fsycl).
+      // as well as in non-sycl mode.
 
-      if (FoundPCH) {
+      if (FoundPCH && !SYCLDeviceCompilation) {
         if (IsFirstImplicitInclude) {
           A->claim();
           CmdArgs.push_back("-include-pch");
@@ -1391,6 +1404,13 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
                                                        << A->getAsString(Args);
         }
       }
+      // No PCH file, but we still want to include the header file
+      // (-include dummy.h) in device compilation mode.
+      else if (JA.isDeviceOffloading(Action::OFK_SYCL) &&
+               A->getOption().matches(options::OPT_include_pch)) {
+        continue;
+      }
+
     } else if (A->getOption().matches(options::OPT_isystem_after)) {
       // Handling of paths which must come late.  These entries are handled by
       // the toolchain itself after the resource dir is inserted in the right

clang/test/Driver/pch-include-sycl.cpp

@@ -0,0 +1,33 @@
+// This test checks that a PCH(Precompiled Header) file is 
+// included while performing host compilation in -fsycl mode.
+
+// RUN: touch %t.h
+
+// PCH file.
+// RUN: touch %t.h.gch
+
+// Linux
+// -fsycl and -include
+// RUN: %clang -fsycl -include %t.h -###  %s 2>&1 \
+// RUN:   | FileCheck -check-prefixes=CHECK-SYCL-HOST,CHECK-SYCL-DEVICE %s
+// CHECK-SYCL-DEVICE: -fsycl-is-device
+// CHECK-SYCL-DEVICE-NOT: -include-pch
+// CHECK-SYCL-HOST: -fsycl-is-host
+// CHECK-SYCL-HOST-SAME: -include-pch
+
+
+// -fsycl and -include-pch
+// RUN: %clang -fsycl -include-pch %t.h.gch -###  %s 2>&1 \
+// RUN:   | FileCheck -check-prefixes=CHECK-PCH-HOST,CHECK-PCH-DEVICE %s
+// CHECK-PCH-DEVICE: -fsycl-is-device
+// CHECK-PCH-DEVICE-NOT: -include-pch
+// CHECK-PCH-HOST: -fsycl-is-host
+// CHECK-PCH-HOST-SAME: -include-pch
+
+// Windows
+// RUN: %clang_cl -fsycl --target=x86_64-unknown-linux-gnu /Yupchfile.h /FIpchfile.h -### %s 2>&1 \
+// RUN:   | FileCheck -check-prefixes=CHECK-YU-HOST,CHECK-YU-DEVICE %s
+// CHECK-YU-DEVICE: -fsycl-is-device
+// CHECK-YU-DEVICE-NOT: -include-pch 
+// CHECK-YU-HOST: -fsycl-is-host
+// CHECK-YU-HOST-SAME: -include-pch