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

[Vladimir Kozlov]

On Mon, 21 Sep 2020 07:07:25 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 (vmSymbolID index : vmSymbolsIterator()) {
>    vm_symbol_index[as_int(index)] = index;
> }
> - 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`.

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" ?

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