RFR: 8330540: Rename the enum type CompileCommand to CompileCommandEnum

[Vladimir Kozlov]

On Wed, 17 Apr 2024 21:26:06 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> `CompileCommand` is used both as a enum type ([compilerOracle.hpp](https://github.com/openjdk/jdk/blob/064628471b83616b4463baa78618d1b7a66d0c7c/src/hotspot/share/compiler/compilerOracle.hpp#L104)), and a global variable ([compiler_globals.hpp](https://github.com/openjdk/jdk/blob/064628471b83616b4463baa78618d1b7a66d0c7c/src/hotspot/share/compiler/compiler_globals.hpp#L304)).
> 
> This makes very awkward to the enum type -- we are forced to use `enum CompileCommand` in the source code whenever a type is needed:
> 
> This simple c++ file illustrates the problem:
> 
> enum class CompileCommand { a, b, c };
> void foo(CompileCommand x) {}
> char* CompileCommand; // can no longer use "CompileCommand" as a type
> void good(enum CompileCommand x) {}
> void bad(CompileCommand x) {}
> 
> $ g++ -c ~/enum.cpp
> /home/iklam/enum.cpp:5:6: error: variable or field ?bad? declared void
>     5 | void bad(CompileCommand x) {}
> 
> 
> The fix is to rename the enum type to `CompileCommandEnum`.
> 
> This also makes it possible to forward-declare `CompileCommandEnum` (see vmEnum.hpp) without including compilerOracle.hpp. This improves HotSpot build time by reducing the number of .o files that include compilerOracle.hpp from 456 to 16.

Good.

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Marked as reviewed by kvn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/18829#pullrequestreview-2007474309