[SYCL][Clang] Permit virtual functions in SYCL (#7255)

To enable virtual functions support in SYCL we need to change virtual
table variables address space, so llvm-spirv translator is able to
generate valid SPIR-V modules.

Author: KornevNikita

clang/include/clang/Basic/LangOptions.def

@@ -293,6 +293,8 @@ LANGOPT(
 LANGOPT(SYCLDisableRangeRounding, 1, 0, "Disable parallel for range rounding")
 LANGOPT(SYCLEnableIntHeaderDiags, 1, 0, "Enable diagnostics that require the "
         "SYCL integration header")
+LANGOPT(SYCLAllowVirtualFunctions, 1, 0,
+        "Allow virtual functions calls in code for SYCL device")
 
 LANGOPT(HIPUseNewLaunchAPI, 1, 0, "Use new kernel launching API for HIP")
 

clang/include/clang/Driver/Options.td

@@ -6614,6 +6614,9 @@ def fsycl_use_main_file_name : Flag<["-"], "fsycl-use-main-file-name">,
   HelpText<"Tells compiler that -main-file-name contains an absolute path and "
            "file specified there should be used for checksum calculation.">,
   MarshallingInfoFlag<CodeGenOpts<"SYCLUseMainFileName">>;
+def fsycl_allow_virtual_functions : Flag<["-"], "fsycl-allow-virtual-functions">,
+  HelpText<"Allow virtual functions calls in code for SYCL device">,
+  MarshallingInfoFlag<LangOpts<"SYCLAllowVirtualFunctions">>;
 
 } // let Flags = [CC1Option, NoDriverOption]
 

clang/lib/CodeGen/ItaniumCXXABI.cpp

@@ -3572,8 +3572,33 @@ void ItaniumRTTIBuilder::BuildVTablePointer(const Type *Ty) {
   // Check if the alias exists. If it doesn't, then get or create the global.
   if (CGM.getItaniumVTableContext().isRelativeLayout())
     VTable = CGM.getModule().getNamedAlias(VTableName);
-  if (!VTable)
-    VTable = CGM.getModule().getOrInsertGlobal(VTableName, CGM.Int8PtrTy);
+
+  // To generate valid device code global pointers should have global address
+  // space in SYCL.
+  bool GenTyInfoGVWithGlobalAS =
+      CGM.getLangOpts().SYCLIsDevice &&
+      CGM.getLangOpts().SYCLAllowVirtualFunctions &&
+      (VTableName == ClassTypeInfo || VTableName == SIClassTypeInfo);
+  auto VTableTy =
+      GenTyInfoGVWithGlobalAS
+          ? CGM.Int8Ty->getPointerTo(
+                CGM.getContext().getTargetAddressSpace(LangAS::sycl_global))
+          : CGM.Int8PtrTy;
+  if (!VTable) {
+    if (GenTyInfoGVWithGlobalAS) {
+      VTable = CGM.getModule().getOrInsertGlobal(VTableName, VTableTy, [&] {
+        return new llvm::GlobalVariable(
+            CGM.getModule(), VTableTy, /*isConstant=*/false,
+            llvm::GlobalVariable::ExternalLinkage, /*Initializer=*/nullptr,
+            VTableName, /*InsertBefore=*/nullptr,
+            llvm::GlobalValue::ThreadLocalMode::NotThreadLocal,
+            llvm::Optional<unsigned>(
+                CGM.getContext().getTargetAddressSpace(LangAS::sycl_global)));
+      });
+    } else {
+      VTable = CGM.getModule().getOrInsertGlobal(VTableName, VTableTy);
+    }
+  }
 
   CGM.setDSOLocal(cast<llvm::GlobalValue>(VTable->stripPointerCasts()));
 
@@ -3585,15 +3610,15 @@ void ItaniumRTTIBuilder::BuildVTablePointer(const Type *Ty) {
     // The vtable address point is 8 bytes after its start:
     // 4 for the offset to top + 4 for the relative offset to rtti.
     llvm::Constant *Eight = llvm::ConstantInt::get(CGM.Int32Ty, 8);
-    VTable = llvm::ConstantExpr::getBitCast(VTable, CGM.Int8PtrTy);
+    VTable = llvm::ConstantExpr::getBitCast(VTable, VTableTy);
     VTable =
         llvm::ConstantExpr::getInBoundsGetElementPtr(CGM.Int8Ty, VTable, Eight);
   } else {
     llvm::Constant *Two = llvm::ConstantInt::get(PtrDiffTy, 2);
-    VTable = llvm::ConstantExpr::getInBoundsGetElementPtr(CGM.Int8PtrTy, VTable,
-                                                          Two);
+    VTable =
+        llvm::ConstantExpr::getInBoundsGetElementPtr(VTableTy, VTable, Two);
   }
-  VTable = llvm::ConstantExpr::getBitCast(VTable, CGM.Int8PtrTy);
+  VTable = llvm::ConstantExpr::getBitCast(VTable, VTableTy);
 
   Fields.push_back(VTable);
 }

clang/lib/Sema/SemaSYCL.cpp

@@ -579,7 +579,8 @@ class DiagDeviceFunction : public RecursiveASTVisitor<DiagDeviceFunction> {
       }
 
       if (const CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Callee))
-        if (Method->isVirtual())
+        if (Method->isVirtual() &&
+            !SemaRef.getLangOpts().SYCLAllowVirtualFunctions)
           SemaRef.Diag(e->getExprLoc(), diag::err_sycl_restrict)
               << Sema::KernelCallVirtualFunction;
 

clang/test/CodeGenSYCL/simple-sycl-virtual-function.cpp

@@ -0,0 +1,33 @@
+// This test checks that the FE generates global variables corresponding to the
+// virtual table in the global address space (addrspace(1)) when
+// -fsycl-allow-virtual-functions is passed.
+
+// RUN: %clang_cc1 -triple spir64 -fsycl-allow-virtual-functions -fsycl-is-device -emit-llvm %s -o - | FileCheck %s  --check-prefixes CHECK,CHECK-PTR
+// RUN: %clang_cc1 -triple spir64 -fsycl-allow-virtual-functions -fsycl-is-device -fexperimental-relative-c++-abi-vtables -emit-llvm %s -o - | FileCheck %s --check-prefixes CHECK,CHECK-REL
+
+// CHECK: @_ZTVN10__cxxabiv120__si_class_type_infoE = external addrspace(1) global ptr addrspace(1)
+// CHECK: @_ZTVN10__cxxabiv117__class_type_infoE = external addrspace(1) global ptr addrspace(1)
+// CHECK-PTR: @_ZTI4Base = linkonce_odr constant { ptr addrspace(1), ptr } { ptr addrspace(1) getelementptr inbounds (ptr addrspace(1), ptr addrspace(1) @_ZTVN10__cxxabiv117__class_type_infoE, i64 2)
+// CHECK-PTR: @_ZTI8Derived1 = linkonce_odr constant { ptr addrspace(1), ptr, ptr } { ptr addrspace(1) getelementptr inbounds (ptr addrspace(1), ptr addrspace(1) @_ZTVN10__cxxabiv120__si_class_type_infoE, i64 2)
+// CHECK-REL: @_ZTI4Base = linkonce_odr constant { ptr addrspace(1), ptr } { ptr addrspace(1) getelementptr inbounds (i8, ptr addrspace(1) @_ZTVN10__cxxabiv117__class_type_infoE, i32 8)
+// CHECK-REL: @_ZTI8Derived1 = linkonce_odr constant { ptr addrspace(1), ptr, ptr } { ptr addrspace(1) getelementptr inbounds (i8, ptr addrspace(1) @_ZTVN10__cxxabiv120__si_class_type_infoE, i32 8)
+
+SYCL_EXTERNAL bool rand();
+
+class Base {
+   public:
+    virtual void display() {}
+};
+
+class Derived1 : public Base {
+   public:
+    void display() {}
+};
+
+SYCL_EXTERNAL void test() {
+  Derived1 d1;
+  Base *b = nullptr;
+  if (rand())
+    b = &d1;
+  b->display();
+}