RFR[xs]: 8245137: aarch64 ICache flush depends on enabling gnu extensions

[David Holmes]

Hi Kim,

On 17/05/2020 3:39 am, Kim Barrett wrote:
> Please review this small change to the aarch64 implementation of
> ICache::invalidate_word ICache::invalidate_range.  Rather than calling
> __clear_cache directly, they are changed to use __builtin___clear_cache.
> The direct call to __clear_cache requires either providing a
> declaration for that function or enabling gnu extensions.  Using the
> builtin requires neither.

Seems perfectly reasonable given we already use it on ARM, and that we 
use other builtins on Aarch64.

Thanks,
David
-----

> CR:
> https://bugs.openjdk.java.net/browse/JDK-8245137
> 
> Webrev:
> https://cr.openjdk.java.net/~kbarrett/8245137/open.00/
> 
> Testing:
> mach5 tier1-5 with -std=c++14 as part of experimental C++14 support.
> mach5 tier1
> 
> Note that there are unrelated build failures with -std=c++98.  Among
> other things, we use va_copy in shared code, which is not available
> until C++11 (because it's a C99 feature), but is made available as a
> gnu extension with -std=gnu++98.
>