RFR(T): 8233530: gcc 5.4 build warning -Wc++14-compat after JDK-8233359

[Kim Barrett]

> On Nov 5, 2019, at 8:44 PM, David Holmes <david.holmes at oracle.com> wrote:
> 
> On 6/11/2019 11:38 am, Kim Barrett wrote:
>>> On Nov 5, 2019, at 2:06 AM, Thomas Stüfe <thomas.stuefe at gmail.com> wrote:
>>> 
>>> Hi all,
>>> 
>>> may I please have reviews for this small build fix:
>>> 
>>> Issue: https://bugs.openjdk.java.net/browse/JDK-8233530
>>> Webrev: http://cr.openjdk.java.net/~stuefe/webrevs/8233530-wc14-compat/webrev.00/webrev/
>>> Prior discussion: https://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2019-November/036726.html
>>> 
>>> Thank you,
>>> 
>>> Thomas
>> The "#ifdef __GNUG__" should not be needed or used.
>> There are a dozen existing uses of PRAGMA_DIAG_PUSH.
>> While there aren't currently any other direct uses of
>> PRAGMA_DISABLE_GCC_WARNING, there are indirect uses via other
>> PRAGMA_DISABLE_xxx macros.
>> None of those have __GNUX__ protections (for any X).
> 
> Well AFAICS they reside in a gcc specific file: compilerWarnings_gcc.hpp. But we also take steps in compilerWarnings.hpp to accommodate their use in source code when other compilers are used.
> 
> #ifndef PRAGMA_DISABLE_GCC_WARNING
> #define PRAGMA_DISABLE_GCC_WARNING(name)
> #endif
> 
> so I agree we should not need any guard to make this gcc only - unless we really do want to control the version.

If we need to control the version it’s applied to, we can use PRAGMA_STRINGOP_TRUNCATION_IGNORED as a model.
Or just version-conditionalize at the one place it’s needed, for now.  If more -Wc++14-compat issues come up later
then we can introduce a new macro.