RFR: 8253402: Convert vmSymbols::SID to enum class

[Coleen Phillimore]

On Wed, 23 Sep 2020 17:05:49 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> src/hotspot/share/ci/ciObjectFactory.hpp line 32:
>> 
>>> 30: #include "utilities/growableArray.hpp"
>>> 31:
>>> 32: enum class vmSymbolID : int;
>> 
>> Do you need this declaration to avoid #include "classfile/vmSymbols.hpp" ?
>
> Yes, that's the intention, because vmSymbols.hpp is big.
> 
> I am thinking whether I should move such forward declarations of enums into globalDefinitions.hpp, so header files that
> use `vmSymbolID` don't need to know that the base type is `int`.

No, don't move them to globalDefinitions.hpp, only have the forward declarations where they're used.  So this is like a
class forward declaration?  neat.

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PR: https://git.openjdk.java.net/jdk/pull/276