RFR: 8297830: aarch64: Make Address a discriminated union internally

[Daniel D. Daugherty]

On Wed, 30 Nov 2022 11:13:35 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change to the aarch64 Address class.  It now uses an
> internal union, separating the literal and nonliteral cases.
> 
> This avoids leaving some fields uninitialized or initializing them to dummy
> values.  It also reduces the size of the Address class somewhat, though it's
> unclear whether that makes any noticeable difference.
> 
> Testing:
> mach5 tier1 for linux-aarch64 and macosx-aarch64
> mach5 tier2-5 for linux-aarch64

Thumbs up. A lot of small touches all over assembler_aarch64.hpp
but the result is definitely cleaner...

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

Marked as reviewed by dcubed (Reviewer).

PR: https://git.openjdk.org/jdk/pull/11429