[SYCL][Driver] Emit unused argument warning for -fno-libspirv (#19135)

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# Based on PR #19134

## Chain of upstream PRs & tree of downstream PRs as of 2025-06-25

* PR #19130

  * PR #19131

    * PR #19134

      * **PR #19135 (THIS ONE)**

          * PR #19136

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Previously the `-fno-libspirv` option was not warned about when there
was no SYCL compilation.
Remove the explicit target check for the targets that support
`-fno-libspirv` and instead rely on each target to emit appropriate
warnings when its used.
This commit slightly degrades diagnostic quality, from

"ignoring '-fno-sycl-libspirv' option as it is not currently supported
for target"
to
"argument unused during compilation: '-fno-sycl-libspirv'"
, but I believe this is acceptable as it allows to remove the list
of targets that support the option from the driver. Additionally,
now if the user mixes targets that support and do not support
`-fno-libspirv` in the same compilation, they will not get warnings
that are not actionable.

---------

Co-authored-by: Alexey Bader <alexey.bader@intel.com>

Author: Maetveis

clang/lib/Driver/Driver.cpp

@@ -1570,19 +1570,6 @@ void Driver::CreateOffloadingDeviceToolChains(Compilation &C,
     }
   }
 
-  // -fno-sycl-libspirv flag is reserved for very unusual cases where the
-  // libspirv library is not linked when using CUDA/HIP: so output appropriate
-  // warnings.
-  if (C.getInputArgs().hasArg(options::OPT_fno_sycl_libspirv)) {
-    for (auto &TT : UniqueSYCLTriplesVec) {
-      if (TT.isNVPTX() || TT.isAMDGCN()) {
-        Diag(diag::warn_flag_no_sycl_libspirv) << TT.getTriple();
-        continue;
-      }
-      Diag(diag::warn_drv_unsupported_option_for_target)
-          << "-fno-sycl-libspirv" << TT.getTriple() << 0;
-    }
-  }
   // -fsycl-fp64-conv-emu is valid only for AOT compilation with an Intel GPU
   // target. For other scenarios, we emit a warning message.
   if (C.getInputArgs().hasArg(options::OPT_fsycl_fp64_conv_emu)) {

clang/lib/Driver/ToolChains/SYCL.cpp

@@ -209,9 +209,18 @@ const char *SYCLInstallationDetector::findLibspirvPath(
 void SYCLInstallationDetector::addLibspirvLinkArgs(
     const llvm::Triple &DeviceTriple, const llvm::opt::ArgList &DriverArgs,
     const llvm::Triple &HostTriple, llvm::opt::ArgStringList &CC1Args) const {
-  if (DriverArgs.hasArg(options::OPT_fno_sycl_libspirv) ||
-      D.offloadDeviceOnly())
+  DriverArgs.claimAllArgs(options::OPT_fno_sycl_libspirv);
+
+  if (D.offloadDeviceOnly())
+    return;
+
+  if (DriverArgs.hasArg(options::OPT_fno_sycl_libspirv)) {
+    // -fno-sycl-libspirv flag is reserved for very unusual cases where the
+    // libspirv library is not linked when required by the device: so output
+    // appropriate warnings.
+    D.Diag(diag::warn_flag_no_sycl_libspirv) << DeviceTriple.str();
     return;
+  }
 
   if (const char *LibSpirvFile =
           findLibspirvPath(DeviceTriple, DriverArgs, HostTriple)) {

clang/test/Driver/sycl-fno-libspirv-warn.cpp

@@ -1,7 +1,7 @@
 /// Test that appropriate warnings are output when -fno-sycl-libspirv is used.
 
-// RUN: not %clangxx -fsycl -fsycl-targets=nvptx64-nvidia-cuda,amdgcn-amd-amdhsa -fno-sycl-libspirv %s -### 2>&1 | FileCheck %s
+// RUN: %clangxx -fsycl -fsycl-targets=nvptx64-nvidia-cuda,amdgcn-amd-amdhsa -Xsycl-target-backend=amdgcn-amd-amdhsa --offload-arch=gfx908 -nogpulib -fno-sycl-libspirv %s -### 2>&1 | FileCheck %s
 // CHECK-DAG: warning: '-fno-sycl-libspirv' should not be used with target 'nvptx64-nvidia-cuda'; libspirv is required for correct behavior [-Wunsafe-libspirv-not-linked]
 // CHECK-DAG: warning: '-fno-sycl-libspirv' should not be used with target 'amdgcn-amd-amdhsa'; libspirv is required for correct behavior [-Wunsafe-libspirv-not-linked]
 // RUN: %clangxx -fsycl -fsycl-targets=spir64-unknown-unknown -fno-sycl-libspirv %s -### 2>&1 | FileCheck --check-prefix=CHECK-SPIR64 %s
-// CHECK-SPIR64: ignoring '-fno-sycl-libspirv' option as it is not currently supported for target 'spir64-unknown-unknown' [-Woption-ignored]
+// CHECK-SPIR64: argument unused during compilation: '-fno-sycl-libspirv' [-Wunused-command-line-argument]

clang/test/Driver/sycl-libspirv-toolchain.cpp

@@ -24,9 +24,9 @@
 // CHECK-DEVICE-ONLY: "-cc1"{{.*}} "-fsycl-is-device"
 // CHECK-DEVICE-ONLY-NOT: "-mlink-builtin-bitcode" "{{.*}}.libspirv-{{.*}}.bc"
 //
-// Only link libspirv in SYCL language mode, but `-fno-sycl-libspirv` does not result in a warning
+// Only link libspirv in SYCL language mode, `-fno-sycl-libspirv` should result in a warning
 // RUN: %clang -### -x cu -fno-sycl-libspirv -nocudainc -nocudalib %s 2>&1 | FileCheck %s --check-prefixes=CHECK-CUDA
-// CHECK-CUDA-NOT: warning: argument unused during compilation: '-fno-sycl-libspirv' [-Wunused-command-line-argument]
+// CHECK-CUDA: warning: argument unused during compilation: '-fno-sycl-libspirv' [-Wunused-command-line-argument]
 // CHECK-CUDA: "-cc1"{{.*}} "-fcuda-is-device"
 // CHECK-CUDA-NOT: "-mlink-builtin-bitcode" "{{.*}}.libspirv-{{.*}}.bc"
 //