RFR: 8351151: Clean up x86 template interpreter after 32-bit x86 removal

[Aleksey Shipilev]

On Wed, 26 Mar 2025 11:51:22 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> x86 template interpreter carries `_LP64`-predicated code blocks that were supporting 32-bit x86. With that port gone, we can clean up the x86 template interpreter. I have checked no superfluous `LP64`, `AMD64`, `IA32` defines are left in affected files.
> 
> Where obvious, I inlined `r15_thread` and `c_arg*`. Left the uses that assign these args to symbolic locals that have meaningful names.
> 
> `verify_FPU` is also no-op now, removed that. There are related cleanups in compilers and runtime we need to do first, before we fully remove `VerifyFPU` flag. This change fans out a little to other platform template interpreters to remove `verify_FPU` as well.
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `tier1`
>  - [x] Linux x86_64 server fastdebug, `all`

Yeah, I only did `r15_thread` inlinings where it made clear sense to do, e.g. where the `Register thread = r15_thread` definition was right near the use, _and_ where no other symbolic locals were introduced (like `robj`). Otherwise I had lots of hunks with the `rthread` -> `r15_thread` rewrites, which made PR 2x larger. So I think we can indeed touch up those as we go later.

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PR Comment: https://git.openjdk.org/jdk/pull/24251#issuecomment-2757704378