[SYCL] Disallow sycl_kernel attribute on host (#4618)

This is essentially a revert of PR #2186, as the supposed
optimization did not materialize. I have removed the
functionality added in that PR, while keeping the code
cleanups.

Author: premanandrao

clang/include/clang/Basic/Attr.td

@@ -1228,7 +1228,7 @@ def SYCLGlobalVar : InheritableAttr {
 def SYCLKernel : InheritableAttr {
   let Spellings = [Clang<"sycl_kernel">];
   let Subjects = SubjectList<[FunctionTmpl]>;
-  let LangOpts = [SYCLIsHost, SYCLIsDevice];
+  let LangOpts = [SYCLIsDevice, SilentlyIgnoreSYCLIsHost];
   let Documentation = [SYCLKernelDocs];
 }
 

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -1042,9 +1042,6 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
   if (D && D->hasAttr<NoProfileFunctionAttr>())
     Fn->addFnAttr(llvm::Attribute::NoProfile);
 
-  if (getLangOpts().SYCLIsHost && D && D->hasAttr<SYCLKernelAttr>())
-    Fn->addFnAttr("sycl_kernel");
-
   if (getLangOpts().SYCLIsDevice && D) {
     if (const auto *A = D->getAttr<SYCLIntelLoopFuseAttr>()) {
       const auto *CE = cast<ConstantExpr>(A->getValue());

clang/lib/Sema/SemaDeclAttr.cpp

@@ -9314,7 +9314,7 @@ static void handleSYCLKernelAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   // Function template must have at least two template parameters so it
   // can be used in OpenCL kernel generation.
   const TemplateParameterList *TL = FT->getTemplateParameters();
-  if (S.LangOpts.SYCLIsDevice && TL->size() < 2) {
+  if (TL->size() < 2) {
     S.Diag(FT->getLocation(), diag::warn_sycl_kernel_num_of_template_params);
     return;
   }

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -6583,27 +6583,6 @@ NamedDecl *Sema::FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
   return D;
 }
 
-static void processSYCLKernel(Sema &S, FunctionDecl *FD, MangleContext &MC) {
-  if (S.LangOpts.SYCLIsDevice) {
-    S.ConstructOpenCLKernel(FD, MC);
-  } else if (S.LangOpts.SYCLIsHost) {
-    QualType KernelParamTy = (*FD->param_begin())->getType();
-    const CXXRecordDecl *CRD = (KernelParamTy->isReferenceType()
-                                    ? KernelParamTy->getPointeeCXXRecordDecl()
-                                    : KernelParamTy->getAsCXXRecordDecl());
-    if (!CRD) {
-      S.Diag(FD->getLocation(), diag::err_sycl_kernel_not_function_object);
-      FD->setInvalidDecl();
-      return;
-    }
-
-    for (auto *Method : CRD->methods())
-      if (Method->getOverloadedOperator() == OO_Call &&
-          !Method->hasAttr<AlwaysInlineAttr>())
-        Method->addAttr(AlwaysInlineAttr::CreateImplicit(S.getASTContext()));
-  }
-}
-
 static void processFunctionInstantiation(Sema &S,
                                          SourceLocation PointOfInstantiation,
                                          FunctionDecl *FD,
@@ -6613,8 +6592,8 @@ static void processFunctionInstantiation(Sema &S,
                                   DefinitionRequired, true);
   if (!FD->isDefined())
     return;
-  if (FD->hasAttr<SYCLKernelAttr>())
-    processSYCLKernel(S, FD, MC);
+  if (S.LangOpts.SYCLIsDevice && FD->hasAttr<SYCLKernelAttr>())
+    S.ConstructOpenCLKernel(FD, MC);
   FD->setInstantiationIsPending(false);
 }
 

clang/test/CodeGenSYCL/sycl_kernel-host.cpp

@@ -1,6 +1,7 @@
 // RUN: %clang_cc1 -std=c++11 -fsyntax-only -fsycl-is-device -verify %s
 // RUN: %clang_cc1 -fsycl-is-host -DHOST -fsyntax-only -verify %s
 
+#ifndef HOST
 // Only function templates
 [[clang::sycl_kernel]] int gv2 = 0; // expected-warning {{'sycl_kernel' attribute only applies to function templates}}
 __attribute__((sycl_kernel)) int gv3 = 0; // expected-warning {{'sycl_kernel' attribute only applies to function templates}}
@@ -14,13 +15,11 @@ __attribute__((sycl_kernel(1))) void foo(T P); // expected-error {{'sycl_kernel'
 template <typename T, typename A, int I>
 [[clang::sycl_kernel(1)]] void foo1(T P);// expected-error {{'sycl_kernel' attribute takes no arguments}}
 
-#ifndef HOST
 // At least two template parameters
 template <typename T>
 __attribute__((sycl_kernel)) void foo(T P); // expected-warning {{'sycl_kernel' attribute only applies to a function template with at least two template parameters}}
 template <typename T>
 [[clang::sycl_kernel]] void foo1(T P); // expected-warning {{'sycl_kernel' attribute only applies to a function template with at least two template parameters}}
-#endif
 
 // First two template parameters cannot be non-type template parameters
 template <typename T, int A>
@@ -46,22 +45,9 @@ __attribute__((sycl_kernel)) void foo(T P);
 template <typename T, typename A, int I>
 [[clang::sycl_kernel]] void foo1(T P);
 
-#ifdef HOST
-// No diagnostics
-template <typename Func>
-void __attribute__((sycl_kernel))
-KernelImpl4(const Func &f, int i, double d) {
-  f(i, d);
-}
+#else
 
-template <typename Name, typename Func>
-void __attribute__((sycl_kernel))
-Kernel(const Func &f) {
-  KernelImpl4(f, 1, 2.0);
-}
-
-void func() {
-  auto Lambda = [](int i, double d) { d += i; };
-  Kernel<class Foo>(Lambda);
-}
+// expected-no-diagnostics
+template <typename T, typename A>
+__attribute__((sycl_kernel)) void foo(T P);
 #endif