RFR: 8253402: Convert vmSymbols::SID to enum class [v5]

[Kim Barrett]

On Tue, 13 Oct 2020 20:51:26 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> Convert `vmSymbols::SID` to an `enum class` to provide better type safety.
>> 
>> - The original enum type `vmSymbols::SID` cannot be forward-declared. I moved it out of the `vmSymbols` class and
>>   renamed, so now it can be forward-declared as `enum class vmSymbolID : int;`, without including the large vmSymbols.hpp
>>   file.
>>   - This also breaks  the mutual dependency between the `vmSymbols` and `vmIntrinsics` classes. Now  the declaration of
>>     `vmIntrinsics` can be moved from vmSymbols.hpp to vmIntrinsics.hpp, where it naturally belongs.
>> - Type-safe enumeration (contributed by Kim Barrett)
>> for (vmSymbolsIterator it = vmSymbolsRange.begin(); it != vmSymbolsRange.end(); ++it) {
>>  vmSymbolID index = *it; ....
>> }
>> - I moved `vmSymbols::_symbols[]` to `Symbol::_vm_symbols[]`, and made it accessible via `Symbol::vm_symbol_at()`. This
>>   way, header files (e.g. fieldInfo.hpp) that need to convert from `vmSymbolID` to `Symbol*` don't need to include the
>>   large vmSymbols.hpp file.
>> - I changed the `VM_SYMBOL_ENUM_NAME` macro so that the users don't need to explicitly add the `vmSymbolID::` scope.
>> - I removed many unnecessary casts between `int` and `vmSymbolID`.
>> - The remaining casts are done via `vmSymbol::as_int()` and `vmSymbols::as_SID()` with range checks.
>> 
>> -----
>> If this is successful, I will do the same for `vmIntrinsics::ID`.
>
> Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Addressed review comments by Kim Barrett

Marked as reviewed by kbarrett (Reviewer).

-------------

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