RFR: 8247909: Improve PrimitiveConversions::cast using C++14

[Stefan Karlsson]

On Sun, 13 Sep 2020 07:27:13 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this reimplementation of PrimitiveConversions::cast,
> using facilities from C++14.  In particular, conversions involving
> only integral values or integral and enum values are now constexpr.
> Also using <type_traits> rather than HotSpot work-alikes.
> 
> Had to update zForwardingEntry.hpp because of a class no longer being
> implicitly included.  Improved a friend declaration while in the
> vicinity.
> 
> Testing
> mach5 tier1

I think this looks good. The patch updates ZForwardingEntry to use std::true_type. Why isn't that done for the handful
other places where we use PrimitiveConversions::Translate?

src/hotspot/share/metaprogramming/primitiveConversions.hpp line 35:

> 33: class PrimitiveConversions : public AllStatic {
> 34:
> 35:   // True if types are the same size and either is integral then int.

I don't get the " then int." part. Is this from an earlier version using "enable if" with types?

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PR: https://git.openjdk.java.net/jdk/pull/143