[SYCL] Ignore 'used' attribute when emitting sycl device code (#1729)

Signed-off-by: Premanand M Rao <[email protected]>

Author: premanandrao

clang/lib/AST/ASTContext.cpp

@@ -10446,14 +10446,14 @@ bool ASTContext::DeclMustBeEmitted(const Decl *D) {
   if (D->hasAttr<WeakRefAttr>())
     return false;
 
-  // Aliases and used decls are required.
-  if (D->hasAttr<AliasAttr>() || D->hasAttr<UsedAttr>())
-    return true;
-
   if (LangOpts.SYCLIsDevice && !D->hasAttr<OpenCLKernelAttr>() &&
       !D->hasAttr<SYCLDeviceAttr>())
     return false;
 
+  // Aliases and used decls are required.
+  if (D->hasAttr<AliasAttr>() || D->hasAttr<UsedAttr>())
+    return true;
+
   if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
     // Forward declarations aren't required.
     if (!FD->doesThisDeclarationHaveABody())

clang/test/CodeGenSYCL/sycl-device-used-attr.cpp

@@ -0,0 +1,37 @@
+// RUN: %clang_cc1 -fsycl -fsycl-is-device -triple spir64-unknown-unknown-sycldevice -disable-llvm-passes %s -emit-llvm -o -  | FileCheck %s
+// Test that the 'used' attribute does not force the emission of globals on sycl device
+
+// CHECK-NOT: @_ZN1hI1aE1iE
+// CHECK-NOT: @_ZGVN1hI1aE1iE
+// CHECK-NOT: @__dso_handle
+// CHECK-NOT: @llvm.global_ctors
+// CHECK-NOT: @llvm.used
+
+// CHECK-NOT: {{.*}} void @_ZN1fI1aEC2Ev(%struct._ZTS1fI1aE.f* %this)
+
+// CHECK-NOT: {{.*}} void @__cxx_global_var_init()
+// CHECK-NOT: {{.*}} void @_ZN1gD1Ev(%class._ZTS1g.g*) unnamed_addr #2
+// CHECK-NOT: {{.*}} i32 @__cxa_atexit(void (i8*)*, i8*, i8*)
+// CHECK-NOT: {{.*}} void @_ZN1fI1aEC1Ev(%struct._ZTS1fI1aE.f* %this)
+
+struct a;
+class g {
+public:
+  int c;
+  ~g();
+};
+template <class>
+class h {
+public:
+  static const void k();
+  static g i;
+};
+template <class j>
+const void h<j>::k() { i.c = 0; }
+template <class j>
+g h<j>::i;
+template <class>
+struct f { f() __attribute__((used)); };
+template <class j>
+f<j>::f() { h<j>::k(); }
+template struct f<a>;