[SYCL][Driver] Fix fno-gpu-rdc SYCL libraries linking not using opaque pointers (#10418)

Fix fno-gpu-rdc SYCL libraries linking not using opaque pointers for
non-SPIR targets.

Issue was when specifiying -fno-gpu-rdc for an opaque pointer target,
there would be object modules with typed pointers. so llvm-link would
need the opaque-pointer flag but that wasn't being added previously due
to relying on the default RDC behaviour where the first call to
llvm-link linking the SYCL libraries with the kernel module is expected
to have the kernel module as the first input. This isn't true in no-rdc
mode, where the first input is a SYCL device library, hence checking the
RDC mode before setting the state of `LinkSYCLDeviceLibs`.

Test checking the behaviour was added as well.

Author: GeorgeWeb

clang/lib/Driver/ToolChains/SYCL.cpp

@@ -223,7 +223,16 @@ const char *SYCL::Linker::constructLLVMLinkCommand(
     };
     size_t InputFileNum = InputFiles.size();
     bool LinkSYCLDeviceLibs = (InputFileNum >= 2);
-    LinkSYCLDeviceLibs = LinkSYCLDeviceLibs && !isSYCLDeviceLib(InputFiles[0]);
+    // Per-object compilation (or non-relocatable device code mode) requires a
+    // change in the link dependencies, such that the first input file is no
+    // longer the prepended kernel BC module. The SYCL device libs are linked
+    // first and the single output is linked with the kernel module separately.
+    if (IsRDC) {
+      LinkSYCLDeviceLibs =
+          LinkSYCLDeviceLibs && !isSYCLDeviceLib(InputFiles[0]);
+    } else {
+      LinkSYCLDeviceLibs = LinkSYCLDeviceLibs && isSYCLDeviceLib(InputFiles[0]);
+    }
     for (size_t Idx = 1; Idx < InputFileNum; ++Idx)
       LinkSYCLDeviceLibs =
           LinkSYCLDeviceLibs && isSYCLDeviceLib(InputFiles[Idx]);

clang/test/Driver/sycl-no-gpu-rdc-opaque-pointers.cpp

@@ -0,0 +1,16 @@
+///
+/// Checks that the SYCL libraries modules are first linked with opaque-pointers, 
+/// when no GPU Relocatable Device Code mode is used.
+///
+
+// UNSUPPORTED: system-windows
+
+// RUN: %clangxx -fsycl -fsycl-targets=nvptx64-nvidia-cuda -fno-gpu-rdc %s --sysroot=%S/Inputs/SYCL -### 2>&1 \
+// RUN: | FileCheck %s -check-prefix=CHECK_NORDC_OPAQUE_PTR
+// CHECK_NORDC_OPAQUE_PTR: clang{{.*}}
+// CHECK_NORDC_OPAQUE_PTR-NOT: llvm-link
+// CHECK_NORDC_OPAQUE_PTR: clang-offload-bundler
+// CHECK_NORDC_OPAQUE_PTR: llvm-link{{.*}}"-only-needed"{{.*}}"-opaque-pointers"{{.*}}libsycl-crt{{.*}}libsycl-complex{{.*}}libsycl-complex-fp64{{.*}}libsycl-cmath{{.*}}libsycl-cmath-fp64{{.*}}libsycl-imf{{.*}}libsycl-imf-fp64{{.*}}libsycl-imf-bf16{{.*}}libsycl-fallback-cassert{{.*}}libsycl-fallback-cstring{{.*}}libsycl-fallback-complex{{.*}}libsycl-fallback-complex-fp64{{.*}}libsycl-fallback-cmath
+// CHECK_NORDC_OPAQUE_PTR-NOT: "opaque-pointers"
+// CHECK_NORDC_OPAQUE_PTR-NEXT: llvm-link{{.*}}sycl-no-gpu-rdc-opaque-pointers{{.*}}libsycl-crt
+// CHECK_NORDC_OPAQUE_PTR-NEXT: sycl-post-link