Add support for sycl_special_class attribute.

Special classes such as accessor, sampler, and stream need additional
implementation when they are passed from host to device.

This patch is adding a new attribute “sycl_special_class” used to mark
SYCL classes/struct that need the additional compiler handling.

Author: zahiraam

clang/include/clang/AST/CXXRecordDeclDefinitionBits.def

@@ -112,6 +112,9 @@ FIELD(HasVariantMembers, 1, NO_MERGE)
 /// True if there no non-field members declared by the user.
 FIELD(HasOnlyCMembers, 1, NO_MERGE)
 
+/// True if there is an '__init' method defined by the user.
+FIELD(HasInitMethod, 1, NO_MERGE)
+
 /// True if any field has an in-class initializer, including those
 /// within anonymous unions or structs.
 FIELD(HasInClassInitializer, 1, NO_MERGE)

clang/include/clang/AST/DeclCXX.h

@@ -1139,6 +1139,9 @@ class CXXRecordDecl : public RecordDecl {
   /// \note This does NOT include a check for union-ness.
   bool isEmpty() const { return data().Empty; }
 
+  void setInitMethod(bool Val) { data().HasInitMethod = Val; }
+  bool hasInitMethod() const { return data().HasInitMethod; }
+
   bool hasPrivateFields() const {
     return data().HasPrivateFields;
   }

clang/include/clang/Basic/Attr.td

@@ -1191,6 +1191,13 @@ def SYCLKernel : InheritableAttr {
   let Documentation = [SYCLKernelDocs];
 }
 
+def SYCLSpecialClass: InheritableAttr {
+  let Spellings = [Clang<"sycl_special_class">];
+  let Subjects = SubjectList<[CXXRecord]>;
+  let LangOpts = [SYCL];
+  let Documentation = [SYCLSpecialClassDocs];
+}
+
 def C11NoReturn : InheritableAttr {
   let Spellings = [Keyword<"_Noreturn">];
   let Subjects = SubjectList<[Function], ErrorDiag>;

clang/include/clang/Basic/AttrDocs.td

@@ -409,6 +409,71 @@ The SYCL kernel in the previous code sample meets these expectations.
   }];
 }
 
+def SYCLSpecialClassDocs : Documentation {
+  let Category = DocCatStmt;
+  let Content = [{
+SYCL defines some special classes (accessor, sampler, and stream) which require
+specific handling during the generation of the SPIR entry point.
+The ``__attribute__((sycl_special_class))`` attribute is used in SYCL
+headers to indicate that a class or a struct needs a specific handling when
+it is passed from host to device.
+Special classes will have a mandatory ``__init`` method and an optional
+``__finalize`` method (the ``__finalize`` method is used only with the
+``stream`` type). Kernel parameters types are extract from the ``__init`` method
+parameters. The kernel function arguments list is derived from the
+arguments of the ``__init`` method. The arguments of the ``__init`` method are
+copied into the kernel function argument list and the ``__init`` and
+``__finalize`` methods are called at the beginning and the end of the kernel,
+respectively.
+The ``__init`` and ``__finalize`` methods must be defined inside the
+special class.
+Please note that this is an attribute that is used as an internal
+implementation detail and not intended to be used by external users.
+
+The syntax of the attribute is as follows:
+
+.. code-block:: c++
+
+   class __attribute__((sycl_special_class)) accessor {};
+   class [[clang::sycl_special_class]] accessor {};
+
+This is a code example that illustrates the use of the attribute:
+
+.. code-block:: c++
+
+   class __attribute__((sycl_special_class)) SpecialType {
+   int F1;
+   int F2;
+   void __init(int f1) {
+     F1 = f1;
+     F2 = f1;
+   }
+   void __finalize() {}
+   public:
+     SpecialType() = default;
+     int getF2() const { return F2; }
+   };
+
+   int main () {
+   SpecialType T;
+   cgh.single_task([=] {
+     T.getF2();
+   });
+}
+
+This would trigger the following kernel entry point in the AST:
+
+.. code-block:: c++
+
+   void __sycl_kernel(int f1) {
+   SpecialType T;
+   T.__init(f1);
+   ...
+   T.__finalize()
+ }
+  }];
+}
+
 def C11NoReturnDocs : Documentation {
   let Category = DocCatFunction;
   let Content = [{

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -11448,6 +11448,9 @@ def warn_sycl_kernel_num_of_function_params : Warning<
 def warn_sycl_kernel_return_type : Warning<
   "function template with 'sycl_kernel' attribute must have a 'void' return type">,
   InGroup<IgnoredAttributes>;
+def err_sycl_special_type_num_init_method : Error<
+  "types with 'sycl_special_class' attribute must have one and only one '__init' "
+  "method defined">;
 
 def err_bit_int_bad_size : Error<"%select{signed|unsigned}0 _BitInt must "
                                  "have a bit size of at least %select{2|1}0">;

clang/lib/AST/DeclCXX.cpp

@@ -111,7 +111,7 @@ CXXRecordDecl::DefinitionData::DefinitionData(CXXRecordDecl *D)
       HasDeclaredCopyAssignmentWithConstParam(false),
       IsAnyDestructorNoReturn(false), IsLambda(false),
       IsParsingBaseSpecifiers(false), ComputedVisibleConversions(false),
-      HasODRHash(false), Definition(D) {}
+      HasODRHash(false), Definition(D), HasInitMethod(false) {}
 
 CXXBaseSpecifier *CXXRecordDecl::DefinitionData::getBasesSlowCase() const {
   return Bases.get(Definition->getASTContext().getExternalSource());

clang/lib/Sema/SemaDecl.cpp

@@ -9170,6 +9170,13 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
         Diag(D.getDeclSpec().getVirtualSpecLoc(), diag::err_virtual_in_union);
         NewFD->setInvalidDecl();
       }
+      if ((Parent->isClass() || Parent->isStruct()) &&
+          Parent->hasAttr<SYCLSpecialClassAttr>() &&
+          NewFD->getKind() == Decl::Kind::CXXMethod &&
+          NewFD->getName() == "__init" && D.isFunctionDefinition()) {
+        if (auto *Def = Parent->getDefinition())
+          Def->setInitMethod(true);
+      }
     }
 
     SetNestedNameSpecifier(*this, NewFD, D);
@@ -16729,8 +16736,21 @@ void Sema::ActOnTagFinishDefinition(Scope *S, Decl *TagD,
       RD->completeDefinition();
   }
 
-  if (isa<CXXRecordDecl>(Tag)) {
+  if (auto *RD = dyn_cast<CXXRecordDecl>(Tag)) {
     FieldCollector->FinishClass();
+    if (RD->hasAttr<SYCLSpecialClassAttr>()) {
+      auto *Def = RD->getDefinition();
+      assert(Def && "The record is expected to have a completed definition");
+      unsigned NumInitMethods = 0;
+      for (auto *Method : Def->methods()) {
+        if (!Method->getIdentifier())
+            continue;
+        if (Method->getName() == "__init")
+          NumInitMethods++;
+      }
+      if (NumInitMethods > 1 || !Def->hasInitMethod())
+        Diag(RD->getLocation(), diag::err_sycl_special_type_num_init_method);
+    }
   }
 
   // Exit this scope of this tag's definition.

clang/lib/Sema/SemaDeclAttr.cpp

@@ -8301,6 +8301,9 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case ParsedAttr::AT_SYCLKernel:
     handleSYCLKernelAttr(S, D, AL);
     break;
+  case ParsedAttr::AT_SYCLSpecialClass:
+    handleSimpleAttribute<SYCLSpecialClassAttr>(S, D, AL);
+    break;
   case ParsedAttr::AT_Format:
     handleFormatAttr(S, D, AL);
     break;

clang/test/Misc/pragma-attribute-supported-attributes-list.test

@@ -155,6 +155,7 @@
 // CHECK-NEXT: ReturnTypestate (SubjectMatchRule_function, SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: ReturnsNonNull (SubjectMatchRule_objc_method, SubjectMatchRule_function)
 // CHECK-NEXT: ReturnsTwice (SubjectMatchRule_function)
+// CHECK-NEXT: SYCLSpecialClass (SubjectMatchRule_record)
 // CHECK-NEXT: ScopedLockable (SubjectMatchRule_record)
 // CHECK-NEXT: Section (SubjectMatchRule_function, SubjectMatchRule_variable_is_global, SubjectMatchRule_objc_method, SubjectMatchRule_objc_property)
 // CHECK-NEXT: SetTypestate (SubjectMatchRule_function_is_member)

clang/test/SemaSYCL/special-class-attribute-on-non-sycl.cpp

@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -std=c++11 -fsyntax-only -fsycl-is-device -verify %s
+// RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify -x c++ %s
+
+#ifndef __SYCL_DEVICE_ONLY__
+// expected-warning@+5 {{'sycl_special_class' attribute ignored}}
+#else
+// expected-no-diagnostics
+#endif
+
+class __attribute__((sycl_special_class)) special_class {
+  void __init(){}
+};