[SYCL] Allow use of function declarators with empty parentheses (#1994)

Treat foo() function as foo(void) instead of a no-prototype function when code is compiled for SYCL devices.

Author: srividya-sundaram

clang/lib/Parse/ParseDecl.cpp

@@ -6391,8 +6391,8 @@ void Parser::ParseFunctionDeclarator(Declarator &D,
     else if (RequiresArg)
       Diag(Tok, diag::err_argument_required_after_attribute);
 
-    HasProto = ParamInfo.size() || getLangOpts().CPlusPlus
-                                || getLangOpts().OpenCL;
+    HasProto = ParamInfo.size() || getLangOpts().CPlusPlus ||
+               getLangOpts().OpenCL || getLangOpts().SYCLIsDevice;
 
     // If we have the closing ')', eat it.
     Tracker.consumeClose();

clang/lib/Sema/SemaType.cpp

@@ -5083,8 +5083,8 @@ static TypeSourceInfo *GetFullTypeForDeclarator(TypeProcessingState &state,
       FunctionType::ExtInfo EI(
           getCCForDeclaratorChunk(S, D, DeclType.getAttrs(), FTI, chunkIndex));
 
-      if (!FTI.NumParams && !FTI.isVariadic && !LangOpts.CPlusPlus
-                                            && !LangOpts.OpenCL) {
+      if (!FTI.NumParams && !FTI.isVariadic && !LangOpts.CPlusPlus &&
+          !LangOpts.OpenCL && !LangOpts.SYCLIsDevice) {
         // Simple void foo(), where the incoming T is the result type.
         T = Context.getFunctionNoProtoType(T, EI);
       } else {

clang/test/SemaSYCL/no-prototype-func.c

@@ -0,0 +1,3 @@
+// RUN: %clang_cc1 -fsycl -fsycl-is-device -triple spir64-unknown-unknown-sycldevice -emit-llvm -verify %s
+// expected-no-diagnostics
+int foo();