RFR: 8340576: Some JVMCI flags are inconsistent

[Tom Rodriguez]

On Sun, 22 Sep 2024 11:51:20 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

> This PR replaces some uses of `UseJVMCICompiler` with `EnableJVMCI` so that JVMCI code paths are taken when JVMCI is only used for non-CompilerBroker compilations.

src/hotspot/share/compiler/oopMap.inline.hpp line 69:

> 67: 
> 68:   #ifndef COMPILER2
> 69:       COMPILER1_PRESENT(ShouldNotReachHere();)

As I noted in a private comment, I think this logic is simply wrong for JVMCI but since we never build JVMCI without C2 we never encounter it.  Derived oops should only be encountered if C2 in available or if EnableJVMCI is true.  I don't really understand the `COMPILER1_PRESENT` guard here either.  It seems like it should be more like:

#ifndef COMPILER2
#if INCLUDE_JVMCI
      if (!EnableJVMCI)
#endif
        ShouldNotReachHere();
#endif // !COMPILER2

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PR Review Comment: https://git.openjdk.org/jdk/pull/21120#discussion_r1771805501