[OpenCL] Allow variadic macros as Clang feature

[Anastasia]

Summary

Variadic macros are used for debugging and therefore it is desirable to accept the code that uses them.

There was a discussion about this in OpenCL spec bugs: https://github.com/KhronosGroup/OpenCL-Docs/issues/50

There was no disagreement on relaxing this , but however we didn't find a way to version this yet.

For now we are allowing this as Clang feature (difference to a standard).

I assume it's not a separate feature and therefore not worth to start Clang extension for this. So I just modified the Clang manual for now. However, I could also start a new section in the extension document: https://clang.llvm.org/docs/LanguageExtensions.html

[Anastasia]

Better wording

[Anastasia]

Fixed comment

[bader]

LGTM. Thanks!

[arsenm]

Should it be downgraded to a warning about an extension instead of just removing it?

[Anastasia]

In D59492#1433796, @arsenm wrote:

Should it be downgraded to a warning about an extension instead of just removing it?

What would you suggest to put in a warning message? Clang normally doesn't warn about extensions...

[arsenm]

In D59492#1434636, @Anastasia wrote:

In D59492#1433796, @arsenm wrote:

Should it be downgraded to a warning about an extension instead of just removing it?

What would you suggest to put in a warning message? Clang normally doesn't warn about extensions...

Isn't that what -pedantic is for?

[Anastasia]

In D59492#1434822, @arsenm wrote:

In D59492#1434636, @Anastasia wrote:

In D59492#1433796, @arsenm wrote:

Should it be downgraded to a warning about an extension instead of just removing it?

What would you suggest to put in a warning message? Clang normally doesn't warn about extensions...

Isn't that what -pedantic is for?

Yes, indeed I think it's a better approach now since it's still in the spec...

[Anastasia]

Instead of removing the diagnostic completely change into a warning in pedantic mode.

[arsenm]

include/clang/Basic/DiagnosticLexKinds.td

397

Maybe rephrase the message now to say it's an extension? The other similar warnings seem to mention "GNU extension" or "Microsoft extensions" or <standard version> extension.

None of them seem to mention "clang" extensions however.

[Anastasia]

Changed diagnostic wording to indicate that this feature is a Clang extension.

[Anastasia]

include/clang/Basic/DiagnosticLexKinds.td

397

Actually I have found a couple of diagnostics with Clang extension so it should be fine.

Thanks for the feedback.

[arsenm]

LGTM

[Anastasia]

Committed in r356987.

include/clang/Basic/DiagnosticLexKinds.td

 def ext_empty_fnmacro_arg : Extension<
   "empty macro arguments are a C99 feature">, InGroup<C99>;
 def warn_cxx98_compat_empty_fnmacro_arg : Warning<
   "empty macro arguments are incompatible with C++98">,
   InGroup<CXX98CompatPedantic>, DefaultIgnore;
 def note_macro_here : Note<"macro %0 defined here">;
 def note_macro_expansion_here : Note<"expansion of macro %0 requested here">;
 
-def err_pp_opencl_variadic_macros :
-  Error<"variadic macros not supported in OpenCL">;
+def ext_pp_opencl_variadic_macros : Extension<
+  "variadic macros are a Clang extension in OpenCL">;
 
 def err_pp_invalid_directive : Error<"invalid preprocessing directive">;
 def err_pp_directive_required : Error<
   "%0 must be used within a preprocessing directive">;
 def err_pp_file_not_found : Error<"'%0' file not found">, DefaultFatal;
 def err_pp_through_header_not_found : Error<
   "'%0' required for precompiled header not found">, DefaultFatal;
 def err_pp_through_header_not_seen : Error<

lib/Lex/PPDirectives.cpp

while (true) {
     case tok::ellipsis:  // #define X(... -> C99 varargs
       if (!LangOpts.C99)
         Diag(Tok, LangOpts.CPlusPlus11 ?
              diag::warn_cxx98_compat_variadic_macro :
              diag::ext_variadic_macro);
 
       // OpenCL v1.2 s6.9.e: variadic macros are not supported.
       if (LangOpts.OpenCL) {
-        Diag(Tok, diag::err_pp_opencl_variadic_macros);
-        return true;
+        Diag(Tok, diag::ext_pp_opencl_variadic_macros);
       }
 
       // Lex the token after the identifier.
       LexUnexpandedToken(Tok);
       if (Tok.isNot(tok::r_paren)) {
         Diag(Tok, diag::err_pp_missing_rparen_in_macro_def);
         return true;
       }

test/Misc/warning-flags.c

 CHECK-NEXT:   warn_undef_interface
 CHECK-NEXT:   warn_undef_interface_suggest
 CHECK-NEXT:   warn_undef_protocolref
 CHECK-NEXT:   warn_weak_identifier_undeclared
 CHECK-NEXT:   warn_weak_import
 
 The list of warnings in -Wpedantic should NEVER grow.
 
-CHECK: Number in -Wpedantic (not covered by other -W flags): 27
+CHECK: Number in -Wpedantic (not covered by other -W flags): 28

test/Preprocessor/macro_variadic.cl

-// RUN: %clang_cc1 -verify %s
+// RUN: %clang_cc1 -verify %s -cl-std=CL1.2
+// RUN: %clang_cc1 -verify %s -pedantic -DPEDANTIC -cl-std=CL1.2
 
-#define X(...) 1 // expected-error {{variadic macros not supported in OpenCL}}
+
+#define NO_VAR_FUNC(...)  5
+#define VAR_FUNC(...) func(__VA_ARGS__);
+#define VAR_PRINTF(str, ...) printf(str, __VA_ARGS__);
+#ifdef PEDANTIC
+// expected-warning@-4{{variadic macros are a Clang extension in OpenCL}}
+// expected-warning@-4{{variadic macros are a Clang extension in OpenCL}}
+// expected-warning@-4{{variadic macros are a Clang extension in OpenCL}}
+#endif
+
+int printf(__constant const char *st, ...);
+
+void foo() {
+  NO_VAR_FUNC(1, 2, 3);
+  VAR_FUNC(1, 2, 3); //expected-error{{implicit declaration of function 'func' is invalid in OpenCL}}
+  VAR_PRINTF("%i", 1);
+}