[OpenCL] Emit opencl.cxx.version metadata for C++ (#92140)

Currently there is no way to tell whether an IR module was generated
using `-cl-std=cl3.0` or `-cl-std=clc++2021`, i.e., whether the origin
was a OpenCL C or C++ for OpenCL source.

Add new `opencl.cxx.version` named metadata when compiling C++. Keep the
`opencl.ocl.version` metadata to convey the compatible OpenCL C version.

Fixes #91912

Author: svenvh

clang/lib/CodeGen/CodeGenModule.cpp

@@ -1399,17 +1399,25 @@ void CodeGenModule::Release() {
 void CodeGenModule::EmitOpenCLMetadata() {
   // SPIR v2.0 s2.13 - The OpenCL version used by the module is stored in the
   // opencl.ocl.version named metadata node.
-  // C++ for OpenCL has a distinct mapping for versions compatibile with OpenCL.
-  auto Version = LangOpts.getOpenCLCompatibleVersion();
-  llvm::Metadata *OCLVerElts[] = {
-      llvm::ConstantAsMetadata::get(llvm::ConstantInt::get(
-          Int32Ty, Version / 100)),
-      llvm::ConstantAsMetadata::get(llvm::ConstantInt::get(
-          Int32Ty, (Version % 100) / 10))};
-  llvm::NamedMDNode *OCLVerMD =
-      TheModule.getOrInsertNamedMetadata("opencl.ocl.version");
-  llvm::LLVMContext &Ctx = TheModule.getContext();
-  OCLVerMD->addOperand(llvm::MDNode::get(Ctx, OCLVerElts));
+  // C++ for OpenCL has a distinct mapping for versions compatible with OpenCL.
+  auto CLVersion = LangOpts.getOpenCLCompatibleVersion();
+
+  auto EmitVersion = [this](StringRef MDName, int Version) {
+    llvm::Metadata *OCLVerElts[] = {
+        llvm::ConstantAsMetadata::get(
+            llvm::ConstantInt::get(Int32Ty, Version / 100)),
+        llvm::ConstantAsMetadata::get(
+            llvm::ConstantInt::get(Int32Ty, (Version % 100) / 10))};
+    llvm::NamedMDNode *OCLVerMD = TheModule.getOrInsertNamedMetadata(MDName);
+    llvm::LLVMContext &Ctx = TheModule.getContext();
+    OCLVerMD->addOperand(llvm::MDNode::get(Ctx, OCLVerElts));
+  };
+
+  EmitVersion("opencl.ocl.version", CLVersion);
+  if (LangOpts.OpenCLCPlusPlus) {
+    // In addition to the OpenCL compatible version, emit the C++ version.
+    EmitVersion("opencl.cxx.version", LangOpts.OpenCLCPlusPlusVersion);
+  }
 }
 
 void CodeGenModule::EmitBackendOptionsMetadata(

clang/test/CodeGenOpenCLCXX/version.clcpp

@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 %s -triple "spir64-unknown-unknown" -emit-llvm -o - -cl-std=CL2.0 | FileCheck %s --check-prefix=CHECK-NO-CXX
+
+// RUN: %clang_cc1 %s -triple "spir64-unknown-unknown" -emit-llvm -o - -cl-std=clc++1.0 | FileCheck %s --check-prefix=CHECK-CXX100
+// RUN: %clang_cc1 %s -triple "spir64-unknown-unknown" -emit-llvm -o - -cl-std=clc++2021 | FileCheck %s --check-prefix=CHECK-CXX2021
+
+// This test checks that opencl.cxx.version metadata is emitted accordingly.
+// It avoids any C++ features to enable checking that the metadata is not emitted in non-C++ mode.
+
+kernel void foo() {}
+
+// CHECK-NO-CXX-NOT: opencl.cxx.version
+
+// CHECK-CXX100-DAG: !opencl.ocl.version = !{[[OCL:![0-9]+]]}
+// CHECK-CXX100-DAG: !opencl.cxx.version = !{[[CXX:![0-9]+]]}
+// CHECK-CXX100-DAG: [[OCL]] = !{i32 2, i32 0}
+// CHECK-CXX100-DAG: [[CXX]] = !{i32 1, i32 0}
+
+// CHECK-CXX2021-DAG: !opencl.ocl.version = !{[[OCL:![0-9]+]]}
+// CHECK-CXX2021-DAG: !opencl.cxx.version = !{[[CXX:![0-9]+]]}
+// CHECK-CXX2021-DAG: [[OCL]] = !{i32 3, i32 0}
+// CHECK-CXX2021-DAG: [[CXX]] = !{i32 2021, i32 0}